May 2010 Archives

Thanks to Mike Ingram of Donovan, Illinois for these shots taken as thunderstorms swept the area Monday afternoon.

Thanks to Harry Quiroz for sharing this shot of the first round of thunderstorms that hit the southern portions of the Chicago area Sunday night.

Thanks to Mary King of Lisle for passing along these shots of the threatening mammatus clouds that preceded this morning's thunderstorms there. The heavy thunderstorms unfortunately washed out the scheduled Memorial Day parade there.

Thunderstorms that swept across the Chicago area Monday were a hit-and-miss affair. Residents in many western suburbs experienced only weak thunderstorms, but damaging thunderstorm winds toppled trees in and around Antioch. And a genuine two-hour deluge swamped Chicago's South Side, the southern suburbs and much of Lake County in Indiana with localized 3-inch totals.

More storms on way
Two storm systems have northern Illinois in their cross hairs this week, and both carry the threat of locally severe thunderstorms and heavy rainfall. Thunderstorms associated with the first system arrive in Wednesday's predawn hours and continue intermittently into early Thursday. The next system arrives Saturday and preliminary indications are that it, too, could be potent.

Dear Tom,
On July 4, 1956, Unionville, Md., got a record 1.23 inches of rain in a minute. What caused the rain to fall so heavily that day?
--Jeff Kozinski, Mokena

Dear Jeff,
It was what is known as a "rain gush," a colloquial term used to describe a sudden, intense rainfall, usually at a rate of 4 inches or more per hour. Gushes are almost always associated with thunderstorms. Incredible bursts of rain producing 2 inches in one minute are occasionally reported.
Very large raindrops fall at a top speed of about 30 feet per second (20 mph), but rising currents of warm air (updrafts) within thunderstorms easily attain much greater speeds. Consequently, thunderstorm updrafts often support immense quantities of water. Should such updrafts suddenly weaken or collapse, their burdens of water will pour out in a sudden gush.

Just wanted to recap the rainfall totals that the forecast area saw on Memorial Day.
A cool front came through late morning and brought thunderstorms with heavy rainfall amounts.  Only two places reported hail, Antioch and Peotone.  Also Antioch reported some extremely strong winds, straight line winds that brought gusts up to 80 mph and trees/powerlines down.
Here are the rainfall totals since 5:40 pm
Momence (Kankakee Cty) 3.52"
Midway 2.97"
Merrillville (Lake Cty, IN) 2.00"
Plainfield 1.81" with nickel size hail
Crown Point 1.62"
Beecher 1.57"
Glen Ellyn 1.32"
Carol Stream 1.09"
Peotone 1.04"
West Chicago .77"
Oak Brook .67"

Thunderstorms are rapidly developing this morning to the west and northwest of Chicago.  Portions of McHenry and Boone Counties have already been hit with heavy downpours and some small hail. 

For more on the storms and when they will arrive here in Chicago, check out the WGN Severe Weather Blog

http://weblogs.wgntv.com/chicago-weather/severe-weather/

 

 

RIGHT:  Radar image from 9:30AM this (Monday) morning

Monday's expected thunderstorms, triggered by the arrival of cooler air, are but the initial salvo in a cycle of active weather that threatens at least a few hours of thunderstorms on four of the next six days.

Storms should move out of the area later Monday, but expect the next wet weather Wednesday and Thursday -- possibly with heavy rainfall -- followed in quick order by another round of thunderstorms late Friday into Saturday.

Agatha triggers landslides

Agatha, the season's first named tropical cyclone in the Pacific basin, brought only 45 mph winds at landfall on Guatemala's Pacific coast late Saturday, but has generated 15-30 inches of rain that is triggering deadly flash floods and landslides in the mountainous interiors of Guatemala, El Salvador and Honduras. Rains are forecast to diminish today.

Dear Tom,
You mentioned that last summer the city recorded only four 90s. Has there ever been a summer without any?
-- Max Friedman

Dear Max,
Only once in Chicago's weather history dating from 1871 has the city experienced a summer without a single 90-degree day, and that was in 1875. The highest readings that summer were 89 degrees on June 11 and 88 degrees on July 15. However, the city's official thermometer in 1875 was located downtown and close to Lake Michigan, and it is almost a certainty that readings reached 90 degrees at inland locations.
The city's official weather observation station was moved inland in 1942 (to Midway Airport) and then to O'Hare International Airport (1980). The fewest number of 90-degree days logged at the inland stations was two in 1979.
Recent summers have produced relatively few 90-degree days, but historic trends indicate the potential for a substantial number of 90s this summer.

Memorial Day weekend weather in Chicago has been known to be finicky. Over the past 137 years, half of the holidays have produced measurable rain and only a quarter have managed highs of 80 degrees or higher. This year's holiday weekend may include rain on Monday.

Near perfect weekend.

That rain aside, Chicago's weather over the majority of the weekend will be as close to perfection as late May weather gets here. The higher-than-normal temperature trend that has dominated much of meteorological spring will be very evident in coming days.

Though humidities will increase in the next few days, the rise isn't likely to become evident until Sunday afternoon when the year's second official 90-degree high is predicted.

Dear Tom,
If warmer air can hold more moisture and should therefore be heavier, why does it rise toward the ceiling when we have our heat and humidifier running?
---Janis Franz

Dear Janis,
A parcel of air will rise whenever it is less dense than the air around it. When air is warmed, the molecules of its component gases vibrate more rapidly, collide more frequently and become more widely spaced, so the air expands and becomes less dense. The effect of moisture is similar.

Contrary to popular belief, moist air is less dense than dry air at the same temperature. The molecular weight of a water molecule is less than the proportionally averaged molecular weight of the gases in air. Consequently, adding moisture to air causes it to become less dense. The conclusion: Air becomes less dense and rises when it is warmed and/or when moisture is added.

Memorial Day weekend weather in Chicago has been known to be finicky. Over the past 137 years, half of the holidays have produce measurable rain and only a quarter have managed highs 80 or higher. This year's holiday weekend may indeed include rain--some of it thundery on Monday. While those rains aren't likely to be continuous, our latest forecast has extended their stay in the area in response to the predicted slowdown of a cold front expected to produce the precipitation.

That rain aside, Chicago's weather over the majority of the weekend will be as close to perfection as late May weather gets here. The warmer than normal temperature trend which has dominated the majority of the meteorological spring season to date will be very evident in coming days.

Though humidities ease higher in the next few days, the increase isn't likely to become evident until Sunday afternoon when the year's second official 90-degree high is predicted to occur. Dew points, a measure of atmospheric moisture, are to reach the mid 60s--a bit below the Gulf-Coast level low 70s recorded during last week's warm spell--but noticeable nonetheless.

While 90-degree readings aren't unheard of at this point in the year, only 28 of the 82 years since 1928 at Midway Airport--34 percent of them--have generated two 90-degree or warmer readings before May's close.

Through Friday, meteorological spring temperatures since March 1 have averaged 51.9-degrees--nearly 5 degrees above the long-term average and more than 3 degrees warmer than the same period last year. The season, which ends midnight Monday night, is well on its way to becoming the area's 4th warmest of the past 140 years.

Summers after warm springs often big 90-degree producers

An analysis of summer 90s in years with warm springs indicates a link in many years. Of the summers which have followed Chicago's seven warmest springs, five recorded 90-degree tallies well above the 23 days which occur here on average. One year--1955--produced 46 days with 90-degree or higher temperatures--just two 90s shy of the record of 48 days of 90s at the South Side site in 1988.

11th day above 70 Saturday, something which didn't happen until mid June last year

Friday's 79-degree high at O'Hare was the 10th consecutive high above 70 degrees. It wasn't until mid-June--nearly three weeks later--that last year's first 10-day stretch of 70s occurred.

Late-season snows whiten mountaintops in the West

While the nation's Heartland was bathed in warm early season weather, up to 4" of snow whitened the Lemhi Ridge observation site in western Montana Friday. The measurement occurred at an elevation of 8,100 feet.

Dear Tom,
Averages, such as daily and monthly average temperatures, are often quoted in the media. How are those averages figured?
--Cynthia Radcliff

Dear Cynthia,
Daily and monthly average temperatures, like averages for other intervals of time, are calculated by determining the arithmetic average using daily maximum and minimum temperatures.
The calculation for a daily average is as follows: Add the day's (midnight-to-midnight, local standard time) maximum and minimum temperatures, divide by 2 and round to the nearest whole number. For a 31-day month, like May, add the 31 daily highs and 31 daily lows, divide by 62, and round to one decimal place.
Long-term averages (the so-called climatological "normal temperatures") are calculated from a 30-year base period, currently using 1971-2000, and updated every 10 years.

No doubt our area beaches will be packed this Memorial Day Weekend.  A sprawling area of high pressure will provide plenty of sunshine and mild to warm temperatures.  The Chicago shoreline water temperature is 65.

Be prepared as you head out to enjoy the surf and sun.  The Chicago National Weather Service office will resume issuing two important products today that will help you plan your outing.  The Surf Zone Forecast will not only give you a weather forecast for the beach but also provide information on tides, waves, and the possibility of rip currents.   The Lakeshore Hazard Message will be issued in the morning whenever their is a moderate or high threat of rip currents.

The Chicago Tribune has an article today on how high-tech the battle on bacteria at our beaches has become.

Last but not least, don't forget to check the UV Index whether you are beach bound or not

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Sun-drenched holiday weekend to foster a rebound in warmth and humidity; some storms possible
 
The Chicago area heads into this Memorial Day weekend positioned for warm weather befitting the holiday which marks the unofficial open to the summer season while honoring those who have served this country. For a holiday juxtapositioned with the year's warmest temperatures, it's ironic how often it's weather has been anything but summer-like.

While it's true sections of the area could see several thunderstorms before the holiday weekend comes to an end, most hours will be rain-free. The best thinking now is that any rain which might flirt with the area would do so late Sunday night, perhaps lingering into early Monday. Rain coverage with those storms is likely to be scattered, involving perhaps 40 to 50 percent of the metro area. But by in large, the weather in coming days looks likely to live up to the highest expectations of those hungry to get outdoors.

With the exception of the 77-degree high predicted Friday, official highs away from Lake Michigan are likely to reach or exceed 80 Saturday, Sunday and Monday.  Only in lakeside areas, where northeast breezes are to blow off cool lake waters Friday and Saturday, will residents have to wait until Sunday and Monday to reach 80.

Temperatures which flirt with 90 Sunday?

The possibility that air sinking and compressing beneath the nose of an incoming jet stream wind max Sunday could nudge temperatures toward 90-degrees appears real. It would mark only the second time this year a temperature that warm has occurred. Warming occurs as air sinks on a broad scale and this meteorological setup has been enough to boost temperatures close to 90 in the past.

Before that happens northeast winds off Lake Michigan are likely to keep lakeside readings a bit chilly.
 
Memorial Day weather has not always cooperated with outdoor enthusiasts in the past
 
Memorial Day weather has run the gamut in Chicago; as cool as 32 degrees in 1992 and as warm as 93-degrees more than a half century ago in 1953. A 91 degree Memorial Day high occurred as recently as 4 years ago.

Rain has fallen on just under half (46 percent) of the 137 Memorial Days for which we have official records.  And rains has been no stranger to the holiday in recent years. Seven of the past ten holidays have recorded at least a trace of rain.

In terms of temperature, only a quarter of the Memorial Days on the books here since 1873 have managed an 80-degree high. There are indications this Memorial Day will join the ranks of the  80-degree producers.

 
NOAA joins other tropical forecasters in issuing ominous 2010 Atlantic basin hurricane season forecast
 
Forecasters at the National Oceanic and Atmospheric Administration's Climate Prediction Center, citing the warmest ocean temperatures in 50 years in the Atlantic basin's hurricane breeding ground, as well as citing the demise of the ongoing El Nino in the equatorial Pacific, issued a sobering forecast Friday for 2010 Atlantic basin hurricane season. The number hurricanes and tropical storms is likely to exceed the averages---and possibly exceed them significantly. The agency's director Dr. Jane Lubchenco didn't mince words. "If this outlook holds, this season could be one of the more active on record."

The forecast comes in an especially challenging year.  Thousands in Haiti---a country prone to the ravages of hurricanes ---remain in tent cities in the wake of the past year's devastating earthquake. At the same time, a catastrophic oil spill is underway in the Gulf of Mexico---a development which could be severely impacted by any hurricanes or tropical storms.

In issuing such a forecast, NOAA forecasters have joined other tropical weather researchers and forecasters at Colorado State and the UK Met Office in predicting what many fear may become an exceptionally active 2010 season.
 
 
 


 

Dear Tom,
Does Hudson Bay have any effect on Chicago weather?
Bill Peters, Beach Park

Dear Bill,
Though Hudson Bay is more than 1,000 miles to our north, its icy waters do play a role in Chicago's weather. That region is a frequent host to large, stationary high pressure systems that keep a sustained northeast flow of air into the Midwest and Chicago. The air of arctic origin is not only cold, but also dry and can bring extended periods of cool and dry weather to Chicago during spring, summer and fall. When this type of flow occurs in winter, the result is often a prolonged period of cloudy, snowy weather. The snow is usually light due to lack of moisture except where the lake-effect from the Great Lakes enhances totals. When low pressure is parked over Hudson Bay in winter Chicago can be in line for major arctic outbreaks and sustained periods of severe cold.

Jim Marocchi from Winfield, IL Hsent us these Wednesday morning sunrise shots taken in Schaumburg.

Thanks for the shots Jim!

Anson Mount sent us this great shot from high above the clouds. HE tells us:

A fellow pilot of mine shot this today near Quincy this afternoon from 37000 feet. Thus cell topped out at 42000!

Thanks for sharing the shot Anson!

 
 
Photo courtesy of Anson Mount, Algonquin

The National Oceanic and Atmospheric Administration (NOAA)--parent agency of the National Weather Service---is out with its 2010 Atlantic Basin hurricane season forecast and it raises warning flag for residents in the country's hurricane prone areas. The 2010 season is to be an active one--potentially "..one of the more active on record." says NOAA chief and under secretary of commerce for oceans and the atmosphere Dr. Jan Lubchenco. 
     The rapid demise of the current El Nino figures prominently in the agency's prediction. El Ninos often thwart Atlantic Basin tropical cyclone activity by increasing winds aloft over the tropical Atlantic. This has the effect of shearing developing tropical disturbances apart before they can organize into tropical storms and hurricanes. Thus, hurricane numbers go down in times of El Nino. The quiet nature of the 2009 Atlantic Basin hurricane season is a perfect example.  But with the current El Nino in full retreat--and the potential, according to longer-range coupled ocean/atmosphere models like NOAA's "CFS" (Climate Forecast System) model,  which attempts to predict weather trends on a seasonal basis, for a comparatively rapid swing from El Nino to La Nina conditions a possibility in the equatorial Pacific as the summer and coming autumn proceed, conditions grow more supportive for tropical cyclone (tropical storm and hurricane) development.
    We'll talk more about this in the days and weeks ahead. But this is NOT good news--and is particularly concerning given the catastrophic oil spill underway in the Gulf of Mexico.
    Read a full summary of NOAA's 2010 Atlantic Hurricane Season forecast here:

http://www.noaanews.noaa.gov/stories2010/20100527_hurricaneoutlook.html


Tom Skilling

The coolest, driest air in a week rides gusty north to northeast winds into the Chicago area Thursday bringing to an end the warmest May 23-26 period in 140 years of record keeping. By day's end, dew points---which reflect atmospheric moisture levels---will have plunged to the low and mid 40s, far from the muggy Gulf Coast-level low 70-degree readings recorded just days ago. The past week has played host to the most humid weather to occur so early in a warm season here in Chicago over the last six years.

The drying process Thursday leads to the demise of the occasionally sprinkly overcast with which the day opens. Clouds are predicted to diminish from the north during the afternoon and skies should be cloud-free by late in the day. Lakeside areas from southeast Wisconsin through northeast Illinois and northwest Indiana will be  on the receiving end of a full-fetch northerly wind flow traveling the length of Lake Michigan's chilliest surface waters Thursday. Those areas are to bear the brunt of the day's cooling, with readings struggling to get out of  the low to mid 60s--- while inland locations reach the mid 70s.

Chicago temperatures this past Sunday through Wednesday (May 23-26) averaged 77.8-degrees---a stunning 17-degrees above the long term average of 60.8-degrees and nearly 15-degrees warmer than the same period a year earlier. In only twelve other years since 1928 have four consecutive days with highs of 85-degrees or warmer occurred at the South Side site. The last time that occurred this early in the season was eight years ago in 2002. Interestingly, the summer which followed went on to produce 32 days with highs of at least 90-degrees.

Warm weather enthusiasts may be interested to learn that the summer months which have followed early-season strings of four or more days with mid-80s have generally gone on to produce an average of 31-days of 90s. That tally is well above the long term average of 23 at Midway Airport.

If this summer ends up producing a large number of hot days, it will end up far different than its four predecessors, each of which has produced only a comparative handful of 90s. Of the 11 years with four or more days in the mid 80s this early in the season, 9 of the 11 summers which followed (82 percent of them) ended up producing more than the average number of 90s at Midway Airport.

Gusty downpours, hail accompany Wednesday afternoon t-storms over 40 percent of metro area

Thunderstorms erupted over portions of the Chicago metro area Wednesday afternoon, at one point prompting urban and small stream flood advisories for sections of Cook and DuPage counties. Doppler scans put cloud tops as high as 46,000 feet and hail---a half inch to an inch in diameter---crashed to earth in wind-driven, lightning-punctuated downpours at a number of locations. Peotone was hit with 1-inch diameter hail.

Lightning data indicated more than 1,800 cloud to ground strokes occurred in a single ten minute period at the height of Wednesday's storms. Heavy rain totals included 1.68 inches at Bartlett in northern DuPage County and 1.03 inches in only 30 minutes near Inverness, located in northern Cook County not far from Schaumburg and Hoffman Estates.
 
 
Downstate cloudburst unleashes 4-inch+ rains just east of state capital
 
Heavy as rains were in some Chicago area storms, several totals downstate were eye-catching. Just a mile east of Springfield, 4.43 inches of rain was reported to have fallen in 90 minutes Wednesday afternoon. A full May in the state's capital typically produces 4.06 inches!
 
 
 


 

Dear Tom,
You recently told us about all the 90s in May 1977. Didn't that May come after one of the city's worst Januarys?
--Donna Winslow

Dear Donna,
You are correct. In one of the most dramatic meteorological turnarounds in Chicago's history, the city's warmest May, with a record 10 days in the 90s, came after the coldest January on record that logged 17 days of zero or below and temperatures that never once reached the freezing mark. January 1977 averaged 10.1 degrees and was 14.2 degrees below normal while May's 69.3-degree average was 9.3 degrees above normal. The summer of 1977 went on to produce 23 more 90-degree days for a total of 33, well above the city's long-term average of 16. The temperature extremes in 1977 spanned 118 degrees, from 19 below zero on Jan. 16 to 99 degrees on July 15.

Skip Talbot sent us this amazing shot taken on a storm chase in South Dakota. Skip tells us:

While storm chasing north central South Dakota on May 22, I witnessed an absolutely
incredible display of nature's beauty and force.  We tracked a cumulus  field north of Perry, SD that erupted from towering cumulus into a mature supercell in only a half hour.  After several cycles of the mesocyclone, the storm put down several tornadoes including a very powerful EF4.  Attached is a picture of this wedge tornado.  Although out of the path of this tornado, we were still close enough to hear the thunderous roar and have our ears start popping.

The structure on the parent supercell was remarkable as well as it maintained a classic supercell mode through most of its life before finally gusting out as a high precipitation supercell.  Here is video from the chase, which you may also find interesting.  I've built a camera enclosure on the roof of my van with pan and tilt servo motors and programmed custom software  that drives it via my laptop.  This allows me to record the entire chase from any angle.  The video I've linked to is three hours of chasing compressed into ten minutes, from the birth of the storm as towering cumulus to its death as an HP supercell, and several tornadoes in between.



SkipTalbot -- May 25, 2010 -- This is time lapsed footage of an entire storm chase through north central South Dakota on May 22, 2010. The video starts with the storm still in the towering cumulus stage and ends with the storm gusting out as an outflow dominant high precipitation supercell, with several tornadoes including a violent wedge in between:

Thanks to Dave Skrzyniarz for passing along this great shot taken earler this afternoon showing the  development stage of the thunderstorms currently hammering the western and northwest suburbs.

Our UV Index of 9 today is as high as it has ever been this year.  Friday and Saturday should be nearly cloudless so the UV Index will stay in the "very high" range for the weekend. 

When you go to slap on the sunscreen be sure you are using sunscreen that is effective.  Not all sunscreens are created equally.  A new study rates sunscreens for their ability to protect skin from both UVA and UVB rays.  The top rated brands are not cheap with some selling for nearly $5 an ounce.

The Environmental Working Group that performed the study warns that people who use sunscreen tend to say in the sun longer because they have a false sense of security.  They advise that the best sunscreen is still a hat and shirt.

The Chicago Tribune and Los Angeles Times has a series of stories on the dangers of too much sun.

www.facebook.com/TimMcGillWeatherGuy

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Daytime heating is likely to coax thunderstorms to life again Wednesday over 40 to 50 percent of the Chicago metro area. Exceptionally light winds above ground suggests these storms aren't likely to hurry along. The thundery deluge which hit Rockford and sections of Wisconsin and Minnesota late Tuesday were products of slow-moving thunderstorms which towered at times as high as 51,000 feet into the atmosphere. 

The downpours of slow-moving thunderstorms can really add up---and quickly. Rainfall in Tuesday afternoon's heaviest thunderstorms fell at rates of up to 1 to 2 inches per hour. Rockford was hit with 1.29 inches of rain and powerful 58 mph gusts. Damage was reported just a mile southeast of the Rockford airport in New Milford Illinois. There, trees and power lines came down in the thundery downpours. Lightning flashed frequently. At the height of Tuesday afternoon's thunderstorms, lightning occurred at the rate of 2,000 discharges in just ten minutes time. A trained spotter reported standing water several feet deep.

At Ogle County's Polo, to Rockford's southwest, street flooding was reported with the same storm complex.
 
Daytime heating provides the perfect environment for thunderstorm development

As sun heats air, it expands and becomes buoyant. Ascending air cools and condenses into cottony cloud masses. These cumulus clouds which become cumulonimbus once the cloud begins precipitating, can grow to altitudes of tens of thousands of feet.  Thunderstorms emanate from the tallest clouds on earth. The unique mix of liquid and ice which occurs in these towering clouds contributes to lightning  formation by separating charges.
  
Wednesday set-up appears one which could support downpours in portions of the Chicago
 
 
The set-up predicted Wednesday will be monitored closely.  With light steering winds aloft, the same moisture-rich pool of air in place here since Sunday remains available to meet the voracious moisture needs of the towering cumulonimbus clouds---or thunderheads---predicted to develop. Projections put the air's water content Wednesday at 1.50 inches---slightly more than was available to the downpour-generating cluster of storms in the west and northwest suburbs Tuesday.

Storms Wednesday are likely to be slow-movers raising the possibility their downpours could again provoke flooding in locations hit by the heaviest rains.

Temp/humidity rebound later this Memorial Day weekend; 80s to stage comeback
 
A break in the recent heat and humidity is on the horizon. By Thursday, north to northeast winds are to travel the length of Lake Michigan into Chicago. Satellite measurements of the Lake Michigan water surface temperatures along the path these winds are to follow will range from 47 to 51-degrees. With winds in contact with such chilly water over the 250+ mile trek from near the Door Peninsula in Wisconsin to Chicago---the air which reaches the city may only be in the 60s---markedly cooler than the string of four consecutive mid 80-degree days which will be on the books by then.
 

Dear Tom,
What would Chicago's weather and climate be like without Lake Michigan?
--Jeff Kozinski, Mokena

Dear Jeff,
Without Lake Michigan on Chicago's eastern doorstep, the city would have a far more continental climate characterized by warmer days, colder nights and a greater daily temperature range. The loss of cooling lake breezes would bring a more uniform temperature distribution across the metropolitan area in spring and summer. Overall there would be a decrease in cloudiness and lower annual precipitation total with the loss of lake-effect snow and rain, lake breeze-generated thunderstorms and the fact that rain-generating frontal boundaries would no longer stall at the south end of the lake. Late fall storms would bring more snow to the city as the northeast winds accompanying them would not carry warm air from 50-degree lake waters inland.

Walt Stagner sent us this shot of cumulonimbus clouds (thunderheads) as viewed from the Fox Valley.

Thanks for the Shot Walt!



Photo courtesy of Walt Stagner, Yorkville, Illinois

For the very latest, check out the WGN Severe Weather Blog

http://weblogs.wgntv.com/chicago-weather/severe-weather/

 

Chicago's weather was in rare form Monday mimicking a July day in every imaginable way. Residents here wasted no time in responding. As on Sunday, a drive up and down the city's packed beaches revealed Chicagoans embraced the late May summer simulation fully!
By the time Monday evening's rush hour was getting underway, 91-degree highs had been logged at both Midway and O'Hare---33-degrees higher than the peak reading of 58 a week earlier---a level 18-degrees above normal. Only 21 of the past 140 years have recorded a temperature or 91-degrees or high this early in the warm season underscoring the rare nature of the hot spell. There hasn't been a warmer May temperature in Chicago in the past 4 years. It was hotter here than in perennial hot spots like Phoenix, Las Vegas, Los Angeles, Miami and Orlando.

Monday's mugginess made it the most humid day this early in a Chicago warm season in 7 years. The city's humidity levels matched those on the Gulf Coast Monday from Brownville to Houston, New Orleans, Tampa and Fort Myers.

Hot as it was at the Chicago's two airport weather observation sites, it was even hotter Monday at a number of suburban locations--among them Darien, Palatine, Des Plaines, Griffith and Highland, Indiana, Plainfield and Hoffman Estates---all of which managed 95 degree highs.

Rockford's 93-degree high Monday tied the 89-year old record for the date set at the site in 1921. It was that city's warmest temperature since early August, 2006.

Chicago wasn't alone with Monday's extraordinary warmth; at least 2 dozen cities across 6 states set heat records

The length and breadth of Monday's summer-level hot air mass was stunning, extending from the Gulf Coast north to Lake Superior and the U.S./Canadian border in Minnesota. Records fell in two dozen cities across six states, including the 95-degree high at the Twin Cities in Minnesota, 94-degrees Moline, 93-degrees Traverse City MI, Stevens Point WI and St. Cloud MN.

Temperatures hit 90 at Marquette, Michigan---hotter than at any point there during the entire warm season last year. The previous 90 to occur there took place on Sept. 2, 2008. 
 
Chicago misses 70 year old record  by just two degrees
 
Monday's 91-degree high missed the record of 93 set in 1950 by just two degrees. The mercury first reached 90-degrees at O'Hare at 12:42 p.m. A 90 was reported only 23 minutes later at 1:05 p.m. on the South Side at Midway Airport.
 
Severe weather pounds the Plains; nearly 300 severe weather report logged with the Storm Prediction Center
 
The eruption of severe thunderstorms within a 1,000 mile-long corridor extending from Texas to the Dakotas produced 16 reports of twisters, 115 of wind damage and 149 of hail---including two reports of hailstones the size of grapefruit. A powerful jet stream running up the western flank of the hot air dome responsible for Chicago's summerlike temperatures Monday in tandem with an influx of energy-rich humid air in the midst of an explosively unstable atmosphere  encouraged air to rise and cool and set the stage for the explosive development of of rotating supercells.
    
Lake Michigan's shoreline water temperature jumped to 61-degrees----6 degrees higher than the same time a year ago
 
Some beachgoers braved Lake Michigan's chilly waters and ventured the into the water Sunday and Monday. Chicago's shoreline water temperature reached 61-degrees--- a new high for the season Monday.

Dear Tom,
The recent question about Chicago's 100-degree temperatures in May prompts me to ask about 100-degree days in June. Have we ever had any?
--Patricia Sanders

Dear Patricia,
In 139 years of temperature data (1871-2009), Chicago's official thermometer has hit or exceeded 100 degrees in June in eight years. That's about one June in 17. Those eight Junes produced 13 triple-digit days, most recently in the drought summer of 1988. But the statistics are misleading because the city's weather observation station was located near Lake Michigan (in the Loop or at the University of Chicago) until 1942, and lake cooling often prevented 100-degree readings that occurred across most of the city. Midway Airport data (1928-2009) provide a better picture: 19 occurrences of 100-degree days in nine Junes out of 82, or one June in nine (versus one in 17 officially).

  Heat built to summer levels Monday. The stunning shift of the past 36 hours away from the early spring-level chill which dominated so much of May to full blown summer heat culminated Monday afternoon in the Chicago area's first official 90-degree highs--the first to occur in May in nearly three years. The heat arrived amid the Chicago area's most humid air of 2010 with Gulf Coast level low 70-degree dew points and followed a record high morning minimum of 73 at the city's Midway Airport observation site. The previous warmest May 24 low had been 72-degrees in 1991. The combination of heat and humidity pushed some area heat indicies to 95-degrees at O'Hare--but as high as 100-105-degrees at the Chicago area's hottest local observation sites.
     Veteran National Weather Service observer Frank Wachowski reports to us the mercury first reached 90 at 12:42 p.m. at O'Hare and 1:05 pm at Midway Airport--the first 90s in well over 9 months since August 9 last year.
      The long term average date for Chicago's first 90-degree reading is on or about June 11 putting the current round of 90s into the Chicago area three weeks early.
     It's not common to see 90-degree temperatures in  May--but it's by no means rare either. Approximately three in 10 Mays records a 90-degree temperature.
     The longest string of May 90s extended across 10 days in 1977.

Other unofficial Weather Bug highs recorded Monday:

95-degrees    Darien, Des Plaines, Palatine
94                 Oswego, Highland IN, Evergreen Park and Elmhurst
92                Frankfort, Lemont
91 Pontiac

     Lake breezes have been tempering the heat along Lake Michigan Monday and will grow even more important in coming days. By Thursday, strengthening northeast winds will lock in forcing temperatures and humidities noticeably lower.
    More on the heat, the cooling expected with a back-door cool front late week and any prospects for a return to hot weather over the coming two weeks on Monday evening's WGN News programs at 5 and 9 PM.

Tom Skilling

    

Summer weather arrived with a flourish Sunday, with area temperatures topping out around 90 degrees and the year's highest dew points, in the upper 60s -- the city's warmest day since August. Even city lakefront areas shared in the warmth as the usual cooling lake breezes failed to dislodge the warm air.

The city will have another shot at the 90-degree mark Monday followed by humid 80s through midweek before a cold front shifts winds into the northeast, dropping temperatures back to more seasonable levels.

Warmest weather ever for Blackhawks

Ironically, hockey held the city's attention on the year's warmest day to date. The previous warmest Blackhawks game in Chicago was an 85-degree day on May 18, 1971, when fog hovered over the ice at the old Chicago Stadium as the Montreal Canadiens captured the Stanley Cup, defeating the Hawks 3-2.

Atlantic disturbance could become season's first tropical storm

A non-tropical disturbance southwest of Bermuda is producing thunderstorms and gale-force winds. As the storm heads northwest the next few days it could acquire tropical characteristics. The Atlantic hurricane season officially begins June 1, with the first named storm to be Alex.

Dear Tom,
I witnessed a tornado in Mapleton, Ill., near Peoria in 1938 from my sixth-grade classroom that blew out windows in our school. Can you provide any details?
-- Bette Stone, DeKalb

Dear Bette,
A family of three or four tornadoes swept across portions of west-central and central Illinois during the afternoon of March 30, 1938. Damage extended from the Quincy area to just south of Peoria. The worst devastation was in South Pekin, where the storm leveled three city blocks. As many as 250 homes were damaged or destroyed, and nine people died. In all, the tornado outbreak claimed 14 lives. While your school escaped major damage, the group of twisters destroyed two schools near Kellerville and severely damaged another near Mount Sterling, where 13 students were injured.

Chicagoans will be turning off furnaces and switching on air conditioners this week as the season's first extended spell of warm and humid weather arrives. Southerly winds will dramatically boost temperatures from Saturday's middle 70s highs into the upper 80s Sunday afternoon along with a dose of Gulf-level humidity as dew points climb into the upper  60s, the highest levels here this season.  The mercury could even reach  90  here on Monday bringing the city its first May 90 in more than three years.  Inland areas will be the warmest as daily lake breezes will keep  shore areas cooler with readings there ranging from the upper 70s to lower 80s. Temperatures will also be warming aloft, an occurrence expected to stifle rain development by putting a "cap" on atmospheric  buoyancy. One caveat, isolated afternoon showers and thunderstorms could develop almost daily as the lake breeze penetrates inland, acting like a miniature cold front.
 
Record heat  in areas south and west

A sign of the approaching heat, temperatures soared to record levels Saturday in areas both west and south of Chicago with new record highs established at Little Rock (94) Valentine, Nebraska (95) and Sioux City, Iowa (92).
 

Dear Tom,
I remember a terrible hailstorm in the Logan Square neighborhood in July 1956. Can you provide details?
---Carole Allen

Dear Carole,
Hail as large as golf balls battered portions of the Chicago area shortly before 6 p.m. on July 19, 1956, as severe thunderstorms swept the city. The hail broke windows and skylights, damaged roofs and siding, and dented cars. A greenhouse near Armitage and California avenues had more than 200 windows broken as the hailstones piled up on the streets and sidewalks. Heavy downpours accompanied the storm, flooding some area basements. At Midway Airport, temperatures in the wake of the storms plunged from 72 degrees to 62 degrees in just a few minutes. This storm occurred two days after severe thunderstorms struck the city with 67 mph winds on July 17.

Thanks to Brett Borchardt for passing along these shots of the thunderstorms that hop-scotched the Chciago area last night. some areas like Aurora and Algonquin received more than an inch of rain, while other spots had little or any rainfall.

 

 

 

Photo by Brett Borchardt

By Tom Skilling, WGN-TV Chief Meteorologist

It's to evolve into one of those magnificent spring weekends many here contend make Chicago's winter chill and snow worth enduring. The clouds and areas of fog which have developed overnight Friday and have grown dense at some locations--are to give way to sunshine and warmer temperatures Saturday--and to do so expeditiously. Visibilities just north of Chicago had dipped to a half-mile or less late Friday evening from Milwaukee south to Kenosha and Waukegan as nighttime cooling converted airborne moisture in the wake of late-day thunderstorms to fog.

The reappearance of sun by mid and late morning Saturday sends weekend temperatures soaring more than 20 degrees above last weekend's readings and to levels not exceeded since last Aug. 15 and 16 when peak Saturday/Sunday readings hit 89 and 88 degrees respectively.

A huge alteration in high-altitude steering winds across the U.S. is driving the warm-up. And once a new warmer pattern is in place, computer models generate atmospheric blocking which is to lock a warm, rain-free atmospheric set-up in place through the coming week.

Though strengthening southerly winds deliver the year's most humid air to date by Sunday afternoon with dew points predicted to approach 70 degrees--a level common on the Gulf Coast--warmth aloft is predicted to stifle rain development. Referred to as a "cap," its presence will discourage air from rising or cooling as vigorously as might otherwise occur in the presence of the near 90-degree ground level temperatures which are being forecast.

The eight latest runs of the National Weather Service's "GFS" (Global Forecast System) model suggest two-week rainfalls may end up close to the long-term averages. But much of that two-week tally is predicted to fall in Week #2--not the first. If this forecast verifies, the closing days of May could end up wetter than the week immediately ahead.

Thundery rains drench portions of the Chicago area; storm damage and flooding sections of northern Indiana and southern Michigan

Thunderstorms swept the Chicago area in waves Friday, unleashing a barrage of lightning and driving downpours both east and west of the city. At one point Friday afternoon, 1,700 cloud-to-ground lightning flashes occurred in a 10-minute period. Only an hour later, the storm's intensity had mellowed noticeably, and the 10-minute lightning tally had dropped to just 500.

Thursday's driving downpours yielded 1.10" at Aurora, 1.09" at Algonquin, 0.96" Carpentersville, 0.88"at Rensselaer, Ind., 0.77" Palatine, and 0.57" at West Chicago and Valparaiso, Ind.

Rainfall proved so prolific from the late-day thunderheads which towered 35,000 feet above Chicago's west and northwest suburbs late Friday that an urban and small screen flood warning was issued for a time across sections of Du Page, Kane, Lake and Mc Henry counties by the National Weather Service. Minor flooding was reported in the Bartlett area.

Farther east, storms in Indiana and Lower Michigan proved the region's most damaging Friday. Thunderstorm gusts at Colon, Mich., downed trees, while Three Rivers, Mich.,--which also suffered tree damage--was walloped by 2.25" of rain in just half an hour.

Blocking pattern to lock warmth, rain-free weather in place

Not only is this weekend's predicted warm-up expected to deliver May 2010's first 80-degree readings, the warmth is predicted to stick around--tempered only by lake breezes predicted to sweep off cool Lake Michigan waters into shoreline areas from northwest Indiana north to Wisconsin.

Dear Tom,
I have noticed there is usually no lightning in tornado videos. Is it uncommon to have lightning in a tornado?
--Steve, Round Lake

Dear Steve,
Tornadoes are one of the dangerous "children" of severe thunderstorms and, while tornadoes themselves probably do not generate lightning, their parent thunderstorms certainly do. Many tornado action videos show lightning in the vicinity of the twisters. That said, it's possible, though unlikely, that a convective cloud (cumulonimbus) might generate a tornado before the storm system has begun to produce lightning.
Because tornadoes usually occur in the rear flank of a thunderstorm complex and are separated from the rain (and lightning) production portion of the storm, lightning may be difficult to see from the camera location if background light is high and the camera is not looking directly into the storm.

National Weather Service co-op observer Pat Skach sent us these photos of ground fog Friday evening in Oak Brook. Thanks Pat for the great images!

Walt Stagner sends us these excellent cloud photos Friday night. The view is looking southwest in Yorkville, Illinois. Thanks Walt!

This evening's showers  produced a double rainbow that was visibile in Lisle. Thanks to Alex King, Christopher Williams and  Josef and Nathan Talaber for passing along this great picture.

Notice the color reversal on the fainter upper bow.

Photo by Mary King

Severe thunderstorms have been roaming across downstate Illinois as well as Indiana this afternoon, while a more subdued brand of thunderstorm is expected here in the metro area.  In addition, dense fog may engulf lakeshore communities later today or tonight.  For more on this, check out the WGN Severe Weather Blog

http://weblogs.wgntv.com/chicago-weather/severe-weather/

 

Right:  Radar image at 11:00AM this (Friday) morning 

It powered Hurricane Katrina to category 5 strength and now it might carry oil towards the Florida Keys and eventually up the east coast.  The Loop Current is a warm ocean current that flows north into the Gulf of Mexico between Cuba and the Yucatan Peninsula, then loops west and south and finally exits the Gulf to the east through the Florida Straits.  This warm "eddy" strengthened Hurricane Camille into a category 3 storm in just one day. Camille went on to become a category 5 monster in 1969.  The loop current also intensified both Hurricanes Katrina and Rita in 2005.

NASA has been taking some stunning images of the oil slick in the gulf.  The images show the oil approaching the Loop Current.  Some believe it has already entered it.  Once in the current, the oil could be carried through the Florida Straits where it could then hitch a ride on the Gulf Stream and spread north along the Atlantic coast.

There are now growing concerns that if the predicted above average hurricane season verifies, the ecological disaster could become even worse.

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Chicago's atmosphere heads into an increasingly volatile state Friday afternoon and evening, one which may well spawn clusters of potentially vigorous thunderstorms. Meteorologists refer to Friday's predicted atmospheric configuration as "unstable"---one in which the decline of temperature with height along with the presence of copious moisture encourage thunderstorm growth. Friday's setup is to become even more impressive as a comparatively cool pool of air aloft rides into the region from the southwest.

Thunderstorms flourished in the same cool pool of air over Missouri Thursday evening. Cloud tops towered to as high as 43,000 according to Doppler radar scan there.  The downpours which accompanied these storms there were impressive producing rain totals of 1.80 inches at Kaiser, 1.52 at Poplar Bluff and 1.05 at Vichy---all in Missouri. Waves of downpour-generating thunderstorms produced by the same system but on a more southerly trek swamped sections of the Deep South depositing 2.69 inches at Hot Springs, 2.39" at Batesville and 2.07 inches at Danville---all in Arkansas.

Model estimates of the quantity water which is to be evaporated in the air over the Chicago area Friday--- 1.30 inches of it---take at least some scattered downpours  a good bet. It wouldn't be surprising to see total rainfall at a few sites---the combination of the bursts of rain which have occurred since precipitation first reached the area late Thursday---to exceed an inch and a half at a few of the harder hit locations.

Rainfall in systems involving thunderstorms is notoriously widely varied because of the highly concentrated nature of the downpours which occur in them---producing narrow swaths doused by heavy totals next to corridors of  much lighter rain.  Computer rainfall estimates with this system generated the past few days have varied from as little as 0.11 inches to as much as 1.99 inches, a spread in totals not unheard of with late spring systems.

Wet pattern isn't likely to last

Strong warming is slated to occur aloft across the nation's heartland in coming days even as unseasonably cool air and high elevation snows whiten mountaintops in the West from California to Utah, Wyoming and Idaho. In time, rising upper level temperatures here are to "cap" or derail rain formation by decreasing the rate at which temperatures drop with height.

With the exception of the threat of a few sprinkles in spots early Saturday and a build-up of a few isolated thunderstorms possible late Saturday---most hours Saturday look likely to be dry. Rain prospects fade completely Sunday and well into next week.
 
Drier than normal weather over all Great Lake basins has lake levels below a year ago
 
The developing dry streak comes as Thursday's weekly report on Great Lakes water levels was released by the U.S. Corps of Engineers. It indicates a continuation of significant year-to-year declines on all the lakes. Lake Michigan's level has tumbled 9 inches compared to a year ago. The Corps estimates each inch Lake Michigan's level changes translates to 390-billion gallons of water. That means Lake Michigan alone has shed 3.51-trillion gallons in the past year thanks to drier than normal weather across its drainage basin---the area from which the lake's water originates.
 
North Woods and U.S./Canadian border areas surge into 80s; drought grips the area
 
While Chicago's afternoon high reached 74-degrees Thursday, peak readings across the North Woods topped out in the 80s. Rhinelander, Wausau and Land O'Lakes in Wisconsin all hit 83-degrees while International Falls, on Minnesota's border with Canada saw 82.
 
Air as warm as Sunday's didn't arrive until late June last year
 
All signs point toward a Sunday high temperature across much of the Midwest at July levels. Chicago's 88 degrees predicted Sunday is to take place amid gusty south winds and in moderately humid mid 60-degree dew point air. It would become the year's highest temperature to date and the warmest reading since last August. Such warmth, while not common this early in the season, isn't by any means rare.  At Midway Airport, 45 of the past 82 years have recorded a temperature of 88-degrees or more by May 23.
 

Dear Tom,
Has a 100-degree temperature ever been recorded in the month of May in Chicago?
---Henry Rosen

Dear Henry,
Officially no. The city's highest May temperature is 98 degrees, recorded on May 31, 1934, with the earliest 100 on record logged the following day when the mercury soared to 102 degrees June 1. However, in 1934 the city's official thermometer was located on the campus of the University of Chicago, close to the cooling breezes of Lake Michigan. Temperatures were much higher inland and triple-digit heat was widespread on that May 31. Midway Airport reached a high of 102 while Aurora peaked at 104, Joliet 101, LaSalle 105 and Rockford and Marengo both recorded 107. That early-season heat wave was just the opening shot of a torrid "dust bowl" summer in which the city would log four official 100s, including the all-time high of 105 on July 24.

Matt Piechota sent us some more storm chase pictures. He tells us:

"Well today we got one tornado near Leedy, OK and then went south due to it becoming very HP'ish and a million chasers, ended up busting south of OKC with a sup that was outflow dominant. Here are a few pics. Friday and Saturday look good as well."


094 is of the large tower as we were on the first supercell from TCU to tornado time

105 is of the funnel cloud before it produced

117 is of the supercell south of norman, OK

#094


#117


#105

Chicago temperatures surged to two week highs away from Lake Michigan Wednesday under the area's first completely cloud-free sky in six weeks. The uninterrupted sunshine stood out in a month which has managed only 44 percent of its possible sunshine---a far cry from the 60 percent considered normal! Had the month ended last evening, the 44 percent tally would have qualified as the cloudiest May here in 19 years. 

Longer days and stronger, more direct sunlight helped contributed to Wednesday's high of 74-degrees---the warmest in two weeks and the sixth official May high to surge above 70 at O'Hare.

Warming continues Thursday with afternoon temperatures headed 3 to 5-degrees higher than 24 hours earlier. But the day's southeast winds coming off Lake Michigan's still-chilly water promise a temperature reduction in lakeshore locations extending from the Indiana shoreline to lakeside areas of Illinois and southeast Wisconsin.

Generous sunshine will have to filter through incoming high clouds Thursday afternoon and evening. The clouds are blowing off powerful thunderstorms to Chicago's southwest which first erupted in the Plains Wednesday where they towered more than 54,000 feet into the atmosphere.
 
Oklahoma raked by tornadoes: spotters report power flashes with one multiple-vortex twister

By late Wednesday evening, NOAA's Storm Prediction Center, the country's clearinghouse for severe weather information, had logged two dozen reports of twisters, including one identified by storm chasers as a "multiple-vortex tornado." The frightening storm touched down south of Norman, Oklahoma, four miles west of Wynnewood. It remained on the ground for more than 7 minutes, dazzling some observers in the area and frightening others by producing power flashes as it took down power lines.

A "rope tornado"---this one with an exceptionally narrow vortex, generally a signal that the twister has entered (or is entering) its dissipating stage---was reported hurling debris through the air near Pierceville, Kansas late Wednesday. Earlier to the south, a "cone" tornado was reported on the ground Wednesday evening just southeast of Marshall, Okla.

Blinding rains accompanied some of the storms, flooding sections of Oklahoma and Kansas. Unnoficial rain totals from the region included 3.78 inches at Broken Arrow, 3.49 at Stillwater and 3.35 at Tulsa--all in Oklahoma.


Chicago area to be swiped by system's northernmost showers/thunderstorms Friday
 
Modest rains, some possibly thundery, reach the Chicago area late Thursday night into Friday, as the northern flank of that Plains storm complex spreads northeastward. Totals in the 0.30 to 0.60 inches appear likely across the Chicago area. But as always when thunderstorms are involved, actual totals are likely to vary widely.
 
80s due Sunday into next week; season's longest string of 80s here in 9 months
 
Summer level warmth, a dramatic change from May's cool ways to date, arrives Sunday and is to feature high temperatures within striking distance of 90-degrees. The most humid air to date in 2010 is to accompany the warm-up with dew points, a measure of atmospheric moisture, rising to the mid to upper 60s. This will lend the air a rather humid "feel." The warm spell is expected to generate 80-degree or warmer highs through mid next week, though lake breezes are to become more of a factor Tuesday and Wednesday lowering shoreline temperatures. 

Sunday and Monday's predicted 88-degree highs are noteworthy. Not only are they 2010's warmest readings to date, their arrival comes nearly a month earlier than the first 88-degree or warmer high a year ago on June 22, 2009.
 

Dear Tom,
Are tornadoes an exclusive curse for the U.S.? I've never heard of them anywhere else in the world.
---Mel Dormer, Aurora

Dear Mel,
The United States records about three quarters of the world's tornadoes, but it does not have exclusive rights. Tornado expert Tom Grazulis has documented significant tornadoes that have produced severe damage and many fatalities in more than 40 countries. Some of the world's tornado-prone areas include Canada, Japan, Australia, Western Europe, South Africa, Russia, Argentina and Bangladesh. The world's deadliest twister is reported to have killed more than 1,300 people in Bangladesh in 1989.
Scientists believe that the number of tornadoes around the world is chronically underreported because of poor documentation and also because many of the twisters are small and weak.

Monsoon: Highly regular seasonal winds that blow steadily from land to sea during the cool season and from sea to land during the warm season. It was first applied to winds over the Arabian Sea, which blow for six months from the northeast and for six months from the southwest. The word is derived from the Arabic mausim, meaning "season".

The primary cause of the monsoon is the much greater annual variation of temperature over large land masses compared with the neighboring ocean surfaces. In the winter, air over the land is colder (generating higher pressure) than air over the water (lower pressure), and wind blows from higher to lower air pressure; that is, from land to water in the winter. In summer, the situation reverses: Air over land is hotter than air over water, and the monsoon blows the other way; that is, from water to land in the summer.

Moist oceanic air moving inland (the summer regime) generates abundant warm-season rainfall in areas subject to the monsoon. By extension, the word "monsoon" is applied to the rain which it brings, though this is technically incorrect.

Matt PiechotaI sent us these pictures of a storm chase in Texas, Matt tells us:

"I was chasing with College of DuPage yesterday in the TX PH and caught three supercells  and 4 tornadoes (2 at night). I however did not get pictures of the tornadoes given at night and moving east of them at the time, the structure on the supercells were simply amazing."

Thanks for the shots Matt!

The days are getting longer and the sun is getting stronger.  We are now enjoying almost six more hours of sunlight compared to late December.  The sun is also delivering more than four times the amount of energy now than it did back in the dead of winter. 

 

Too much exposure to the ultraviolet rays of the sun can be dangerous.  There are more than 2 million cases of non-melanoma skin cancer are diagnosed each year in the United States.  There are nearly 70,000 cases of melanoma, the most serious kind of skin cancer, reported each year.  More than 11,000 die each year due to skin cancer.

You can prepare yourself each day by checking the UV index.  The index indicates the strength of solar UV radiation on a scale from 1 (low) to 11+ (extremely high).

The American Cancer Society has some great advice on how to protect yourself from harmful UV rays.

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Seasonal warming has sputtered in May. The shift in the Chicago area's temperature trend since April has been eye-catching. Evidence is all around us. April's impressive 6.8-degree temperature surplus---one of the biggest on record---has been replaced by a May deficit of just over a degree. The shift has meant city baseball fans have attended games in weather more typical of autumn and the football season than of spring. At the same time, crop and other plant development has been slowed on the area's farms and gardens. Jackets and sweaters have been integrated into Chicagoans' wardrobes regularly in recent weeks.

But big changes loom. Temperatures surge into the 70s away from the lake Wednesday for only the sixth time this month. (Note: A typical Chicago May sees 17 days with highs 70-degrees or higher.)

The simple fact is, maintaining chilly weather isn't easy as May trudges into its final weeks. Days have been lengthening since late December and the Midwest is bathed in more than five and a half additional hours of sunlight each day. And not only is there more of it, the sunshine which pours down on the area is both stronger and more direct. It delivers 4.2 times the solar energy of sunlight just 5 months ago. At the same time, Lake Michigan's waters continue to warm---albeit slowly---and the Canadian and Upper Midwest snow pack is gone.  

Let the sun shine this time of the year---as it will Wednesday and much of Thursday---and it's pretty hard for temperatures not to respond by warming---and warming significantly at that! As always in spring, the wildcard will be wind direction and strength and any cooling the chilly lake waters introduce.

The most significant warming and a healthy injection of Gulf moisture appears likely to take place on Sunday. It's a set-up that could pop an isolated thunderstorm (more widespread showers and thunderstorms may sweep the area Friday.) But warming aloft late this weekend and into next week may well have a precipitation-inhibiting "capping" effect which bodes well for a continuation of warm air well into next week---especially inland.

Tuesday's 65-degree high---while an improvement over Monday's 58---still finished below normal. It was the 13th day of the past 14 to post a cooler than normal daytime highs.

Steamy summer followed a similar April/May temperature regime in 1921
 
Warm weather enthusiasts may find this interesting. With the temperatures of April and May at both ends of the temperature spectrum, we wondered what sort of summer has followed in years with a similar temperature trend---i.e. a warm April and markedly cooler start to May. Only 1 year over the 140-year term of Chicago's weather record matched that temperature trend: 1921. In the summer which followed, the city logged 23 days at or above 90-degrees---twice the long term average number of 90s on the books up to that point. Note: Chicago's earliest weather observations were taken at a site so close to the lake that the record bears a "cool bias," as evidenced by the low number of summer 90s on record up to 1921.
 
Plains brace for severe weather outbreak
 
Vigorous thunderstorms threaten to produce severe weather again Wednesday in the Plains. A total of 25 reports of tornadoes were filed with NOAA's Storm Prediction Center Tuesday and sections of five states---including Texas, Oklahoma, Louisiana, Arkansas and Kansas---could be ground zero for Wednesday's storms
 
Warmest temps in 9 months to be accompanied by 2010's muggiest air Sunday/Monday
 
Not since August have a succession of mid 80s been recorded here. Yet that's what appears likely to happen Sunday and Monday. Dew points, a measure of atmospheric moisture, surge to the year's highest level---a development likely to give the late weekend warmth a very summerlike feel.
 
 

Dear Tom,
What is the largest diameter hail ever reported in the Chicago area?
---Russell Smith
 
Dear Russell,
Hail occurs several times each year in the Chicago area, mainly during the spring and summer thunderstorm season. Most of the hail that falls here is small, usually pea to marble size (0.25 inch to 0.50 inch) but during severe thunderstorms hail up to golf-ball size 1.75 inches) is not uncommon. Earlier this spring, on April 5, baseball-size hail (2.75 inches) fell at Des Plaines; and prior to the devastating F-5 Plainfield tornado in August 1990, tennis-ball size hail (2.50 inches) fell at Joliet. Checking the record books, the area's largest documented hailstones were the size of grapefruits (4 inches) that fell near Kankakee on June 8, 1981, and near Yorkville on May 12, 2000.
 

On Sunday, May 18, 1980, around 8:32 a.m. -- 30 years ago -- Mount St. Helens, dormant since about 1855, erupted violently. The mountain had been rumbling for several weeks prior to May 18 and volcanologists from the U.S. Geological Survey knew an eruption was imminent, but they had no way of knowing exactly when it would blow. Magma had been rising into the mountain and a massive bulge had developed on its north face (see photograph).
 
Here's a picture of Geologist Don Swanson measuring growth of the bulge on the north slope of Mount St. Helens on April 27, 1980---three weeks before the eruption:

USGS photo

Measurements indicated the bulge was expanding by 1.5 meters (4.9 feet) per day. At 8:32 a.m., a magnitude 3.3 earthquake beneath the mountain caused the unstable north flank to slide, essentially unleashing the magma chamber. The eruption began. One blast pushed upward, but a much larger horizontal blast occurred simultaneously.

Geologist Dan Swanson was one of many scientists monitoring Mt. St. Helens and he has the comments:

"We thought the eruption would be vertical like a normal volcanic eruption, although we knew there was a possibility that there could be a flank failure. But we thought these things were rare. We didn't know much about it. A big lesson was that, indeed, there can be a massive failure of volcano flank. The result of the failure is a debris avalanche. People started recognizing debris avalanches around the world, like at Mt. Shasta in California. A light bulb came on. Within one to two years roughly 100 avalanches were recognized around the world. It was a marvelous kind of awakening."
 
"Mt. St. Helens eruption was important because it was so well observed. It provided a kind of model for jump-starting volcano monitoring around the world. Existing observatories got increased funding and people learned how to respond."

It's rare for a May to reach its 18th day without a single 80-degree temperature to its credit in Chicago---but that's JUST what's happened this month. Only 24 of the past 140 years have done so.

The shortage of 80s is being driven by a cooler overall pattern which has dominated the month. Twelve of the past 13 days have been cooler than normal and the month is running nearly a degree below the long-term average--a far cry from April's unseasonable warmth which ended up producing the month's impressive 6.8-degree temperature surplus and an unprecedented five 80s.

Northeast winds off still-chilly Lake Michigan, the presence of extensive cloudiness and the sluggishness with which the low pressure system, mired in an atmospheric blocking pattern, is traversing the Midwest are all behind a continuation Tuesday of the recent blustery chill.

Monday downpours drench areas downstate with more than 2 inches of rain

The storm produced healthy rains in Chicago's Indiana suburbs  Monday with totals as high as 0.69 inches at Rensselaer,  0.56 Griffith, 0.49 Valparaiso and 0.44 inches at Chesterton. But it was areas even farther downstate which bore the brunt of the storm. Unofficial rain totals reached 2.29 inches at Weather Bug locations in Springfield, 1.34 Lincoln, 1.10 Bloomington and 1.08 inches at Peoria. 

Jet stream winds have split into two branches to the west of this system---one heading to the north; another passing to the south. With the strongest steering winds on either side of the system, prospects for the storm leaving the area expeditiously are limited. That's why sustained clearing and the warming encouraged by the return of sunshine holds off until Wednesday.

There are growing indications strong warming, including Chicago's warmest temperatures in the 9 months since August, arrives with the year's most humid air to date this weekend. Afternoon dew points Saturday and Sunday may flirt with 70-degrees, levels typical of those on the Gulf Coast this time of year.
 
Lake winds keep Chicagoans shivering in 50s even as 80s reach Dakotas, Montana and Canada
  
A cloud cover's ability to restrict daytime heating was on full display across the nation's Heartland Monday. While Chicagoans shivered through a 58-degree chill and the area's coolest suburbs,  including Wilmette and Glencoe ,managed highs of only 50 and 51-degrees respectively, bright sun well west propelled highs into the 80s across Montana north into Canada's Prairie Provinces. Highs included 86-degrees at Missoula, 85 at Havre, 84 Bozeman and 82-degree Billings and Great Falls---all in Montana.

 
NOAA reports April the planet's warmest on record; the January to April period the warmest ever
 
The National Weather Service's parent agency NOAA---an acronym for the National Oceanic and Atmospheris Administration----reports the planet's mean temperature in April was 58.1-degrees----1.37-degrees above the 20th Century average. The January through April average global temperature of 56-degrees was also the warmest on record since 1900.
 
35 percent of Mays since 1928 have produce 90-degree temps beyond the eighteenth
 
Cool as it's been, fast temperature turnarounds can occur in May. Such a warm-up is predicted this weekend. All the indicators point to the development of a huge dome of warm, humid air this weekend.

Weather records since 1928 at Midway Airport indicate 35 percent of the past 81 Mays have hosted 90+ degree temperatures in the month's remaining days and that the chances for 90-degree or warmer temperatures rise to 80 percent in the next month.

Dear Tom,
How many tornadoes occur each year in the state of Illinois?
Tom Banas Channahon
 
Dear Tom,
Based on 1953-2004 data from the Storm Prediction Center and the National Climatic Data Center Illinois ranks seventh in the nation averaging 35 tornadoes each year. Texas leads all states with 139 annual twisters followed by Oklahoma 57, Kansas and Florida each with 55, Nebraska 45, and Iowa 37. The majority of the Illinois twisters are of the weak F0 or F1 variety with just 25 percent of them considered strong to violent in the F2-F5 category. Illinois took the brunt of this nation's worst tornado disaster, the famed Tri-State tornado of March 18, 1925 cut a 219 mile long damage path from southeast Missouri across southern Illinois into southwest Indiana killing 695 people and injuring at least 2000.

This was taken across from the famous St. Louis arch Friday as we wrapped up an amazing What a hard working group and how great to work with them. Jim Reed was a terrific guide--we couldn't have done it without him! 

Our team ended up traveling 2,500 miles during last week's storm chase.  We checked and found that's the equivalent of driving from New York City to Las Vegas!  What an amazing week! Thanks to all who followed our trip online and on WGN and for the wonderful feedback so many of you shared with us!

Tom Skilling

4.37" of rain has fallen this May so far, more than doubling the average rainfall and more rain will fall today.  While the Chicagoland area is hoping for some dry weather, parts of our country are begging for some rain.

The Northwoods of Wisconsin, the upper peninsula of Michigan and even Hawaii are experiencing abnormally dry weather.  The U.S. drought monitor notes that northern Wisconsin and portions of the U.P. are enduring a "severe drought".  Historic low lake levels are being reported in Vilas and Oneida counties.  The forecast for this upcoming week is keeping things dry.

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Low pressure tracking east along the Ohio River will spread clouds and a band of showers to the north Monday and Tuesday. While the southern and central portions of Illinois and Indiana could receive from a half inch to an inch of rain from this system, Chicago should rest on the northernmost edge of the rain area. While clouds and a threat of showers will persist through Tuesday, cool gusty winds will blow out of the northeast today and north to northeast Tuesday.

Warm-up expected midweek
High pressure will take hold starting Wednesday, and as skies clear, temperatures will begin to warm. While some computer models place another low pressure system to our south around Friday, there are current indications that the cloud pattern and rains will stay well south. Should that be the case, a gradual warming and extended dry period could extend well into the following week.

Dear Tom,
I saw a reference to "the five horsemen of thunderstorms" and that one throws me for a loop. Do you know what that means?
-- Silvana Scibona

Dear Silvana,
"The five horsemen of thunderstorms" is a reference to the five weather phenomena associated with thunderstorms: wind, hail, rain (and flooding), lightning and tornadoes. All are spawned by thunderstorms and all are potentially damaging and deadly.
Lightning is the defining characteristic of a thunderstorm, and National Weather Service weather observation rules state that a thunderstorm is in progress only when nearby "lightning is seen or thunder is heard."
The cloud that produces thunderstorms is cumulonimbus, once described by University of Chicago graduate Dr. Walter Lyons as "an amazingly efficient weather factory." Worldwide, it is estimated that 16 million thunderstorms occur annually.

With high pressure centered over the northern Great Lakes and low pressure moving slowly east through the Ohio Valley, cool easterly winds and cloudy skies will be the rule over northeast Illinois and northwest Indiana Sunday through Tuesday. Most of the rain associated with the low pressure center will fall over southern and central Illinois and a good portion of Indiana. Sitting on the northern edge of a shower band, the best chance of light showers in the Chicago area will be Monday into early Tuesday and primarily in southern sections. Little daily variation in temperatures is expected, ranging only about 10 to 15 degrees, from the upper 40s to near 60 degrees with coolest readings along the lakefront.
 
Warm up later in the week

As the low moves into New England, high pressure will take over. Light winds and abundant sunshine each day will enable a gradual warming trend beginning Wednesday with high temperatures in the upper 70s, some 5 to 10 degrees above normal, by next weekend.
 

Dear Tom,
What is the most serious volcano threat in the continental United States? What effect could that volcano have on Chicago's weather?
--Laurence Buckingham, Chicago

Dear Laurence,
The "supervolcano" that lies beneath Yellowstone National Park constitutes this country's greatest volcano threat. It has generated three "recent" eruptions (2.1 million years ago, 1.3 million years ago and 640,000 years ago) that were truly gigantic. The U.S. Geological Survey describes those events as "cataclysmic."

A comparable eruption today would have worldwide climatic consequences, probably plunging the planet into a multiyear "volcanic winter." For the United States, it would be a catastrophe. Several feet of volcanic ash would likely bury much of the country (including the Midwest), which, combined with a sharply colder climate, might render agriculture impossible.

After what promises to be a seasonably pleasant weekend, a rainmaker heading for Chicago is expected to bring another round of significant soaking to the city by Monday. So far, this month has logged 4.37 inches of rain, nearly an inch more than the full-month average of 3.38 inches, making the start of May the wettest here since 1990. So far this month has logged four days with 0.5 inches or more of rain and Monday could be the fifth -- just one day shy of the record of six recorded in six Mays, most recently 2004.

80s could be on horizon
After an April that produced five summery days in the 80s, May has turned cool and failed to produce a single day. The cool weather trend is expected to continue at least into the middle of next week before a shift in the jet stream sets the stage for a long overdue warm-up that could finally bring a return of 80-degree warmth to the area by next weekend.

Dear Tom,
Where did the old saying of "Red skies at night, sailor's delight ... ," originate?
--Georgiana Burns, Grayslake

Dear Georgiana,
Variations of this proverb can be traced to biblical times. The complete adage is "Red skies at night, sailor's delight. Red skies in morning, sailors take warning" -- and it does have some validity in mid-latitudes where most weather systems move from west to east. A red sunset suggests the western sky is clear, indicative of high pressure bringing expectations of another day or two of good weather. However, a red sunrise can result from the rising sun illuminating cirrus clouds blowing in from the west. These high clouds are often forerunners of approaching storms, thus giving the sailors an early warning of impending bad weather. Sailors, shepherds and farmers have long relied on weather lore to help them carry out their activities.

What a week it's been!  We've traveled 2,349 miles since our storm chase got underway last Saturday---and we're not done yet.  We're back in Illinois and enjoying the spectacular weather we're now encountering, having spent the night in St. Louis where we uplinked back to Chicago for our WGN Midday Friday News program.  We had a chance to take a few minutes to talk on that broadcast with our storm chase guide Jim Reed, who's been nothing short of spectacular in guiding across huge chunks of Kansas, Oklahoma and Missouri over the past week. We've all bonded after a week on the road together.  Can't tell you how much I think of this team.  I can't even imagine how any other group would have responded with anything near the speed and professionalism which was exhibited as we encountered the multiple vortex twister which literally chased us down Highway 10 in far northern Oklahoma Monday afternoon.  We were all so busy taping and filming the whole situation unfolding, there wasn't much time to ponder the very real fact that thing could have swept all of us up and sent us airborne.  We literally watched as it pulled trees out of the ground and downed powerlines.  There were flashes of light as tranformers and lines came down. My word---WHAT an experience that was.  Then to be engulfed two days later in a lightning-punctuated cloudburst beneath a line of 60,000 ft. tall supercells---storms which rendered visibility zero! It's a miracle we managed to stay on the road. The credit for that belongs to Pam Grimes who was driving in Monday's twister AND in Wednesday's deluge!  On top of being the world's most spectacular producer, Pam's driving skills in absolutely impossible travel conditions might well lead to new job offers ---and we MUST NOT LOSE PAM!!

Tom Skilling and his crew are still tracking twisters in the heart of tornado alley.  They are also trying to spot supercells.  The two actually go hand in hand. Supercells are thunderstorms with a deep, rotating updraft.  The updraft in a thunderstorm provides the fuel of warm, moist air to drive its engine.  Supercells are the rarest type of thunderstorms and the most dangerous.  They are known to produce some of the largest, most violent and long lasting tornadoes.

Here is the official definition from the American Meteorological Society:

supercell--An often dangerous convective storm that consists primarily of a single, quasi-steady rotating updraft, which persists for a period of time much longer than it takes an air parcel to rise from the base of the updraft to its summit (often much longer than 10-20 min).

Keep up with Tom and his team by clicking here.

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The Chicago area can look forward to a dry weekend giving residents a chance of dry out from a thorough soaking by two major precipitation systems this week. While the city officially logged a weekly total of 2.58 inches at O'Hare International Airport, some areas, especially those north and west of the city, received 4 to 5 inches, the majority of it falling in the second rain episode early Thursday. Repeat rounds of thunderstorms caused widespread urban-type flooding that contributed to a nightmarish commute in those areas as overnight rainfall topped 3 inches in many locales. The downpours were triggered by a strong warm front that then sent the mercury skyrocketing from the upper 40s to nearly 80 degrees in less than nine hours Thursday.
May's total rainfall has reached 4.37 inches, surpassing the full-month average of 3.38 inches, making this the sixth wettest May open since 1871.

No rain until Sunday

High pressure should ensure dry weather here through the weekend. The next bout of rain isn't expected before Sunday night giving soils time to dry out and allowing rain-swollen rivers and streams to slowly recede.

Dear Tom,
I lived in Iowa during the summer of 1993 with the terrible flooding. How did Chicago fare that summer?
--Douglas H. Hanbury, East Peoria

Dear Douglas,
The floods of 1993 were benchmark events for much of the Midwest and Plains and are considered to be the costliest and most devastating in the U.S. in modern history. Countless levees failed, inundating many towns as the Mississippi and Missouri rivers and their tributaries reached record crests. The floods were responsible for nearly 50 fatalities and property damage was estimated at more than $20 billion. That summer, Chicago received 20.15 inches of rain making it the city's third wettest on record. June was the wettest month with nearly 10 inches of rain. Though the Chicago area was spared major flooding, short-term flooding did occur here, mainly in the wake of the summer's sporadic heavy thunderstorms.

   Our Skilling Storm Chase team is eastbound on I-44 just outside Springfield , Missouri intent on intercepting potentially strong thunderstorms later Thursday afternoon and evening near the Arkansas/Missouri border.  It's pouring on us and powerful t-storms are moving out of Arkansas across the Missouri border to our southeast. There's a severe thunderstorm watch out in that area.

Overnight rain has resulted in some serious flooding, and Flash Flood Warnings are in effect for much of the Chicago area.  For the very latest, check out the WGN Severe Weather Blog

http://weblogs.wgntv.com/chicago-weather/severe-weather/

Thursday starts out cool, but a warm front will move north through the area in the morning and a cold front approaches from the west in the afternoon. As a result, warm moisture-laden air will flow into northeast Illinois pushing temperatures almost 30 degrees higher than Wednesday, from the middle 40s to the mid-70s. The storm prediction center places northeast Illinois and northwest Indiana in a severe storm outlook area, with the best chance of strong thunderstorms over Chicago this afternoon and northwest Indiana later this afternoon into the evening hours.

Rain-free weekend

High pressure moves into the Midwest and western Great Lakes on Friday and is expected to hold over this area through the weekend. A low pressure system is forecast to develop in Texas and move into the Ohio Valley on Monday, with Chicago and northwest Indiana situated on the northern edge of the associated rain area.

Dear Tom,
I understand the Midwest receives a large amount of moisture and rain from the Gulf of Mexico. Shall we expect the moisture and rain that comes up from the Gulf to carry with it the pollution from the current oil spill?
--Karee McBride

Dear Karee,
We should not. It's true that humid air from the Gulf of Mexico is a potent source of Midwestern precipitation, and as much as 70 percent of Chicago's precipitation (rain and snow) originates with moisture from the Gulf. However, evaporation of water from the Gulf, or any other source, occurs on a molecule-by-molecule basis. Water molecules are not chemically bound to any pollutants that might be present in the water -- oil, for example, or other dissolved solids such as salt. Only pure water evaporates into the air, and all other materials remain in the water.

Oh my word--forgive us as we take a moment to catch our breath!! We've just emerged from a hair-raising, white knuckle trip through blinding thunderstorm downpours which obliterated visibility for more than 20 minutes as we made our way S L O W L Y through southeast Kansas. During that time, we literally had NO visibility---I mean visibility was ZERO--a situation complicated by continuous flashes of cloud to ground lightning, crashes of thunder, hail bombarded our vehicle creating a deafening roar. We are parked in a field outside just south of Norwich Kansas catching or breath and marveling we came through the last half hour in one piece.  Temperatures had dropped from a once muggy 82 to an almost chilly 57 at the height of the storm.  They recovered to 68 at the time of this blog's posting.

It's 4:30 pm--yet it looks like late evening. The sky has darkened, temps are falling and lightning is flashing frequently.  A quick listen to the AM radio reveals near continuous sferics and the rains have begun. There is a decided greenish cast to the sky.  We're in the open fields of Kansas and radar reveals the incoming line possesses cloud tops as high as 59,000 ft. The storm which generated the multiple-vortex twister which chased us Monday a little south of here in northern Oklahoma had cloud tops scanned between 46,000 and 50,000 ft. Our in car thermometer shows the temperature--once in the low 80s is down to 63. More storms feeding into this area from Oklahoma.  We've just entered Kingman County. Lightning increasingly frequent.

Skies as we proceed west are growing ever darker as we continue westbound on Highway 160 in Harper, Kansas. Warnings have been issued with the squall line we're approaching and, for the first time this trip, increasingly frequent cloud to ground lightning can be seen. A tornado warning has been issued based on a radar-detected circulation and the line has a history of large hail production. 

We're on the road west of Wichita heading for severe storms west of the city moving rapidly northeastward. Tornado watch is out and it's muggy, warm and windy and in the low 80s. 

   Wednesday greetings to all!  We arrived back in Wichita, Kansas around 1:30 am this morning after a day long trip out to the rolling plains of western Oklahoma-not far from the Texas Panhandle.  There, the terrain rolls gently and wheat fields extend to the horizon in all directions.  What an amazing place from which to watch the weather!  It's really quite beautiful!

Finding a bite to eat in rural Oklahoma late at night isn't easy. But storm chasers can smell a Sonic burger miles away. We had just ordered when Reed Timmer from the Discovery Channel's Storm Chaser series pulled into the same drive-in with none other than the DOMINATOR. It's a heavily armored car designed to get up close to tornadoes. Check it out! Post by Pam Grimes / Photo & headline by Steve Scheuer

The 4th worst severe weather outbreak of the season struck the plains on Monday and with almost two dozen tornadoes reported, there were two fatalities.  The number killed from Monday's outbreak has been revised from five to two.  Three critically injured children who were missing were eventually found.

As bad as it was, it should not have come as a surprise for folks in Kansas and Oklahoma.  The Storm Prediction Center in Norman, Oklahoma had outlooked the area for a chance of severe weather several days in advance.  The SPC routinely issues "convective outlooks" that outline areas of the country that have the potential for severe weather.  The risk levels range from slight to moderate to high.  A portion of the plains was in a high risk area.  According to the SPC's web site, the high risk "implies that a major severe weather outbreak is expected, with large coverage of severe weather and the likelihood of extreme severe (i.e., violent tornadoes or very damaging convective wind events). The high risk category is reserved for the most extreme events with the least forecast uncertainty, and is only used a few times each year."

Even with better technology and improved forecasts officials are concerned that some people in tornado prone areas are "desensitized" to the danger of these powerful storms.  Sirens were wailing and the sky was threatening but people seemed to ignore the danger.  There were reports of heavy traffic in Norman despite a tornado forming near the city.

Tom Skilling is tracking twisters all this week.  Click here to keep up with the latest on Tom and his team.

Low pressure moves northeast out of the Plains on Wednesday generating a potential for severe storms for a third straight day. It appears that the strongest storms Wednesday will center on eastern Kansas, where Tom Skilling's chase team will start out, and northern Missouri. The threat of severe storms will exist along a wide path from western Texas into Illinois, with Chicago resting on the extreme eastern edge. Heavier storms will approach northeast Illinois Wednesday night; damaging winds and hail are a possibility, but heavy downpours and potential localized flooding are the more likely scenario.

Wet start to May

Tuesday's 0.96 inches of rain at O'Hare International Airport pushed Chicago's official total rainfall for May 2010 to 2.75 inches, the 19th wettest May start since observations began back in 1871. Should at least another inch fall Wednesday night and Thursday, the month would move up to the 11th wettest as of May 13th.

Dear Tom,
How many days of rain does Chicago average in a summer?
--Liz Principe

Dear Liz,
In an average summer, Chicago can expect measurable rain (0.01 inch or more) to fall on 29 days during the 92-day period from June 1 through Aug. 31. That's 32 percent of the days, or about one day out of three. That is the result of a computer scan of Chicago's official precipitation file -- 139 years of data from 1871 through 2009.
But .01 inch of rain will barely dampen your shirt. A substantial rain, say 0.25 inches or more, falls on average 12 of summer's 92 days, or one day out of eight. However, Chicago's summers are not as rain-soaked as those statistics might suggest. Most summer rain falls during thunderstorms; the rain is intense but of short duration. Even a day with heavy rain typically features many rain-free hours.

What change from Monday! The sun's out brightly Tuesday and warming is underway. It's a stunning turnaround from Monday when southeast howled, skies were shrouded in clouds, there was drizzle and temperatures languished in the  60s.  Monday was one of those days which made a good thick jacket feel awfully good! 

There's nothing like an encounter with a multiple vortex tornado, especially when it chases you down the highway at 55 mph, to capture people's imagine and get the phones ringing. I talked this morning about our rendezvous with the twister Monday on the Fox News Channel's Happening Now program with Jane Skinner as well as with Greg Jarrett of WGN radio, Eric and Kathy and our own Mark Suppelsa on The Mix and with Robin Marsh, midday anchor of Oklahoma City's KWTV.  

Wet weather will be the rule in the Chicago area for the next few days as two storm systems promise to bring the city some heavy rainfall. The first round of rain should make for a wet morning commute Tuesday with the showers tapering to sprinkles by early afternoon. Another round of showers and thunderstorms is due to arrive by Wednesday evening and continue into Thursday. With ample moisture feeding into the Midwest, rainfall totals here are likely to be in the 1- to 3-inch range, turning what has been a precipitation deficit here into a surplus. Through Monday, May has produced 1.79 inches of rain and needing only 1.59 inches more to reach the full May average of 3.38 inches which is likely to occur in the next few days.

Plains hammered

Violent thunderstorms erupted Monday across Kansas and Oklahoma, spawning a major severe-weather outbreak that included more than three dozen tornadoes, some deadly. In addition to the twisters, grapefruit- to softball-size hail battered portions of Oklahoma near Cherokee and Marietta.

Dear Tom,
In a previous column you stated the 1964 Good Friday earthquake in Alaska was the strongest in the U.S. How did it compare to the 1811-13 New Madrid quakes?
--Robert Doehler, Glenview

Dear Robert,
The 9.2 magnitude Alaskan earthquake on March 28, 1964, was the strongest quake to ever hit North America. The series of New Madrid quakes that struck the mid-Mississippi Valley between 1811 and 1813 were not as strong, with magnitudes estimated between 7 and 8, but were thought to have an area of strong shaking two to three times larger than the Alaska quake. According to the U.S. Geological Survey, the absence of seismographs and the few people in the New Madrid region at the time leaves the magnitude of these quakes subject to interpretations of journals, newspaper reports and other accounts. A recently released USGS report hints the magnitude might have been as low as 6.8.

    What a day it's been here in the Plains! With extensive damage, deaths and scores of injuries across Oklahoma, Monday's storm outbreak been has evolved into a national story. We saw 4 of the 31 twisters reported across the region during our storm chase Monday---and the number of tornado reports is rising. 

      

 We were chased Monday by a multiple vortex tornado around 3:30pm this afternoon on Highway 11 just south of Wakita and west of Medford in Oklahoma--a little south of the Kansas line. We first spotted one twister on the ground. No sooner had we stopped than the multiple vortex storm was right on top of us. That was frightening! 

        We plan to show you the video we shot this afternoon just after the open of our WGN News at Nine and, later in the broadcast, will also report on just how the work of storm chasers is assessed by other meteorological professionals. 

      Our week on the road storm chasing is only beginning. There are indications Mother Nature isn't done with severe weather production yet. More is expected and we'll be updating you on that in the days to come.

     

It wasn't clear we were going to outrun it! A multiple vortex twister literally developed overhead just outside Wakita and chased after us as we raced up Highway 11 toward Medford OK Monday afternoon.  Wakita, ironically, is the town in which the movie Twister was shot. 

While Tom and the WGN Storm Chase Team continue to follow destructive thunderstorms in southern Kansas, the tornado outbreak that began earlier this afternoon is expanding south into central and eastern Oklahoma.   Some of the most substantial tornado damage is occurring around and just to the east of Oklahoma City.

Even the meteorologists at the National Weather Center had a close encounter when a funnel cloud, or developing tornado, passed directly overhead at 5:33PM.   This funnel rapidly developed into a large and devastating twister less than a mile away.  In fact,  this long track tornado is still on the ground at 6:30PM,  ripping its way through eastern Oklahoma.  Dozens of homes have been destroyed with no word on any injuries at this time. 

 

UPDATE 5:30PM: The WGN Storm Chase Team has broken off pursuit of the tornado that resulted in damage in Hunnewell, KS and  Medford, OK.   The team is now headed north on I-35 toward Wichita hoping to intercept another supercell that may be producing a tornado. 

====================================================================

Tom Skilling and the WGN Storm Chase Team have been following a tornadic supercell that has been raking across far northern Oklahoma since 3:45PM.  This tornado will be moving into southern Kansas shortly with the WGN crew in hot pursuit. 

Here is a list of some of the damage this storm and its associated tornado have been responsible for:

4:43PM:  Tornado damage in Hunnewell, KS with trucks flipped

4:36PM:  Spotters report a tornado on the ground in 8 miles NE of Braman, OK

4:28PM:  Law enforcement reports two tornados on the ground 2 miles south of Hunneywell, KS

4:08PM:  Large tornado on the ground 6 miles east of Renfrow, OK

3:58PM:   Houses with damage from a tornado in Clyde, OK

3:58PM:  Chaser vehicle (hopefully not Tom's) with all of its windows blown out from baseball sized hail

3:43PM:  Significant damage in Medford, OK from a tornado.   

 

Things really starting to look stormy as we continue chasing southwest of Wichita. Skies growing darker, raindrops hitting the windshield. Non-thunderstorm winds have been howling--part of the "low-level jet"--the strong band of southerly winds carrying moisture into the area. Interestingly, we're heading into Wakita, Oklahoma--setting for themovie Twister and home to the Twister museum. Radar detecting supercell storms to our southwest towering to 50,000 ft. We see other stormchasers as we continue along. Raindrops hitting the windshield with increasing strength and the skies heading are growing ever darker and more ominous. It's clear we're nearing these supercells--which are off to our southwest and racing along at 50 mph--incredible!!

The Storm Prediction Center has just issued a "PDS" (Particularly dangerous situation) Tornado Watch across Kansas and our chase area until 10PM.  Watches of this sort aren't issued everyday--to put it mildly! Radar shows thunderstorms developing rapidly over southwest Kansas--Doppler scanned cloud tops already up to 43,000 ft. This is all very consistent with the high resolution computer model forecasts we've been monitoring which suggest supercells will continue developing along the dry line and race eastward embedded within a 100+ mph jet.  It can't be understated just how potent a severe weather situation this is.  We are on the road and heading west and are in intercept mode. We'll continue updating you and have more on WGN News at 5 & 9PM and continuously online!  

Tom Skilling, and fellow meteorologists Mike Phelps and Terry Swails from WQAD pour over the latest computer models.  Kansas is ripe for violent weather today and the possibility of multiple tornadoes is very real!  It may not happen until late in the day-they believe 5-7 Chicago time may be the stormiest!

Mother nature is putting on a spectacular show in Iceland.  The Northern Lights have been visible above the ash being spewed by the aviation altering volcano.  At its worst, the volcanic ash affected over a million travelers a day.  The estimated impact on the airlines is near 2 billion dollars.  In the midst of this natural disaster there has been some natural beauty though.  Iceland is no stranger to the Aurora Borealis but when it coincides with a major volcano eruption it is truly a rare event.  Click on the photo to see more spectacular images from Reuters.

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After a Mother's Day with abundant sunshine, clouds return Monday as low pressure organizes and begins to move northeast out of the southern Plains. Warm southerly flow aloft will be forced to rise and condense as it rides up the cooler, denser air in place over the Midwest. Clouds will be on the increase with showers possible later in the day. Thunder and heavy downpours overnight into Tuesday morning could result in widespread inch-plus totals across the Chicago metro area. A moderate threat of severe storms and tornadoes will center over portions of Kansas, Missouri and Oklahoma Monday afternoon and evening.

More rain expected
The first low pressure system will exit east Tuesday, with a brief 24-hour intrusion of high pressure before the next low pressure system ejects out of the southern Plains. Clouds will be on the increase Wednesday as the second low approaches with moisture-laden thunderstorms and accompanying downpours likely Wednesday night into Thursday.

Dear Tom,
Why does it never rain when it's extremely hot? When the mercury hits 90 degrees or higher, it never seems to rain at the same time. Why is this, and what is the record heat for a day that had rain?
-- Barbara Provus

Dear Barbara,
Chicago's highest temperatures -- near or above 100 degrees -- invariably occur only when a hot air mass, already in place, is further heated by several hours of sunshine. Without plenty of sun, the city's temperatures won't climb to extreme levels and remain there. If overcast assembles and rain approaches on an exceptionally hot afternoon, temperatures tumble before the rain arrives.
That happened on June 20, 1988, the city's hottest day that also had rain. The temperature stood at 104 degrees around 4 p.m., but clouds moved in as a thundershower approached. By the time rain began at 5:15 p.m., it was 91 degrees, and 77 shortly thereafter.

Potentially historic tornado producing storms are bearing down on Kansas in the next 24 hours.

Greetings from cloudy, cool and windy Wichita KS--where Sunday afternoon temperatures sit in the 60s and trees are waving in brisk southeast winds. Sprinkles fall on occasion and the jackets we've brought along feel awfully good! As unlikely as a simple glimpse of conditions at the moment would make it seem, we--and all who reside in this area of the country---sit smack dab in the middle of a zone assessed as a "moderate" severe weather risk by NOAA's Storm Prediction Center (SPC) for Monday into Monday night. As all of you who follow that agency's severe weather predictions know, for SPC to place any region in a "moderate" risk a day ahead of time----well, it's rare to say the least and an indication the country's premiere severe weather monitoring agency has turned an eagle eye toward the region and is quite concerned about the scenario expected to unfold! No wonder! Model forecasts paint an ominous picture.  So  much so, I don't think it would be surprising at all to see that storm risk assessment nudged up to a "high" risk as we get closer to what looks like a potentially significant severe weather outbreak centered on Kansas and Oklahoma at that time.  Could it be we've stumbled into near perfect timing for a series on storm chasing???  It sure seems that way.  And it's not the last time this week severe weather may threaten this region.  More's due mid-week as well. 

He's simply remarkable! No other way to describe extreme weather photographer and our storm chase guide during the coming week Jim Reed, who's photographic credits include National Geographic, Time magazine, the New York Times, the Discovery Channel, all of the American networks--and the list goes on and on.  

Thanks to Tama Pickford of Chesterton, Indiana for passing along this great rainbow  shot taken Saturday afternoon near the Crown Point exit on I-65. With very unstable conditions due to the cold air above the surface showers developed across much of the Chicago metro area.Some of the showers produced very small hail. With sunshine peeking between the clouds, several rainbows were observed in the area.

Courtesy WSI (RPM model)

Humid Gulf air, shown in this Monday afternoon forecast off the RPM computer forecast in the yellow and orange region, and dry air out of the Rockies and desert Southwest depicted here in blue, is likely to be the zone along which strong and potentially severe thunderstorms erupt. Dew points may vary from single digits (amazingly dry air) over western Texas and southwest Kansas (the fire danger in those areas is predicted to be high) to the upper 60s in eastern and central Kansas, Oklahoma and Texas. The set-up for severe weather doesn't get much better than this.

Courtesy WSI (RPM model)

Meteorologists use a parameter known as CAPE to quantify the energy available in the atmosphere to produce thunderstorms. CAPE values mid and late Monday afternoon are to be high in the areas depicted in orange.

With clearing skies and light winds overnight, temperatures dropped into the 30s across northeast Illinois, southeast Wisconsin and northwest Indiana. Early Sunday morning as temperatures bottomed-out, a frost was expected over a good portion of the Chicago area at locations away from the city. As the cold air fed into the western Great Lakes Saturday, temperatures in the Chicago area were mostly in the 40s under cloudy skies with northwest winds gusting over 30 mph. Scattered light afternoon showers included small hail at times. A 3 to 7-inch snowfall covered Upper Michigan and parts of northern Wisconsin.

Storms return

With an active weather pattern across the region, two storm systems are expected to bring showers and thunderstorms to the Chicago area in the week ahead. The first should arrive late Monday into Tuesday with the second batch slated for later Wednesday and Thursday. Chief meteorologist Tom Skilling will be getting an early look at these developing storms during his storm chase this week. He starts out in Kansas on Monday and his trek can be followed on WGN-TV, the Chicago Tribune, and on  the web at wgntv.com.

We're now between Des Moines and Kansas City.  WGN-TV satellite truck operator Bill O'Toole and Photojournalist Jordan Guzzardo will stop for the night in Kansas City.  Tom Skilling, Pam Grimes, Steve Scheuer, and Chicago Tribune photographer Zbigniew Bzdak will drive on to Wichita.  Tom is getting a chance to see what kind of severe weather may greet us and there's some scary stuff on the horizon.  Join us for our first "live" report Sunday night where we'll get to know our storm chase guide Jim Reed.  Find out which hurricane caused him to videotape a good-bye to his Mom.  

Dear Tom,
I recently heard my grandmother talking about the Ice Saints? Who are they?
--Katarina Wisniski

Dear Katarina,
Many European cultures have legends pertaining to late-spring cold spells that frequently bring May frosts, a reminder that plants and crops must still be protected. According to the Glossary of Meteorology, the Ice Saints are St. Mamertus, St. Pancras and St. Savertius (or St. Gervais), whose feast days fall on May 11, 12 and 13 respectively. Some refer to these as the "Three Chilly Saints". Other names for the late season chill include Cold Sophie and, in Germany, the "Eismanner" or "Icemen Days." Similarly, retired Chicago weatherman Paul Kubecka tells us of the "Zelezny Muzi" or "Iron Men," a Czech legend about three fishermen who survived, though badly frozen, after a strong cold front rapidly dropped temperatures while they were fishing on a warm spring day.

Greetings from the road in Iowa! So much goes into the prep of a major news series like the one on which we are embarking, word that our start time had been moved up wasn't passed on to this forecaster!!  But all's well---we're well underway--even had time for a bite to eat.  We've even managed to get our "on the road" Internet connection up and running. This is going to enable me and the incredible WGN team which whom I'm traveling, to keep you up with what looks to be an interesting rendezvous with what could be a blockbuster severe weather outbreak in the Plains early this week.  And, it may not be the last. Models suggest the first storm spins up in the Plains and heads into the Midwest and that a second system could be in the works later in the week.  What timing! We may well have some interesting weather to show you, putting it mildly.      

 At first glance---it's cloudy and cool here as we get underway with an occasional sprinkle---hardly the sort of weather pattern which anyone would dream was the prelude to tornadoes and severe weather. But the remarkable array of computer forecast models we have at our fingertips these days--something we'll be talking about in our WGN News series which coincides with our storm chase and air all this week (starting Sunday with our introduction to extreme weather photographer Jim Reed on the 9PM News)---indicates otherwise. What could end up the most significant severe weather outbreak in the Heartland to date this year appears to be coming together starting Monday. ALL the elements are there. Temperatures and humidities in the Plains predicted to take off as roaring 70+ mph low level southerly winds assemble within a mile of the ground Monday. At the same time dry air surges east from the deserts and a 100+ mph jet westerly jet stream rips into the region overhead.  Energy indicies are high and the directional shift in wind with height is stunning. Storm Prediction Center meteorologists are saying the ensemble of severe weather supportive weather conditions due to assemble from Texas north into Oklahoma and Kansas are on a par with those which have produced strong tornadoes historically.

Tom Skilling and the WGN crew check the latest weather radar data from a Buffalo Wild Wings near Iowa City, Iowa.  Not sure how many times Tom has said WOW so far!

Professional Storm Chaser and photographer Jim Reed is reporting Monday to possibly be a "very active severe weather day in the Central Plains." 

Tom made it, and only 90 minutes late!  Here's our crew for the storm chase all this week on WGN & CLTV News at 9pm for sure and as many other newscasts as we can!

It's Saturday morning and the WGN-TV storm chase is ready to roll.   But wait, where's the big man-Tom Skilling?  Waiting patiently for Tom to show... waiting, waiting...


 

Left to right Zbiginew Bzdak-Chicago Tribune photographer, Steve Scheuer, WGN Photojournalist, Bill O'Toole, Satellite Truck operator, Pam Grimes, Producer, and Jordan Guzzardo, WGN Photojournalist.  

Thanks to Steve Taylor for passing along these shots taken Friday during a rare May snow in Gilman, Wisconsin northwest of Wausau. Areas of northern Wisconsin and Michigan's upper peninsula were expecting as much as 7 inches of snow. While much of the snow should melt, some will likely remain on the ground early Sunday giving the area a rare white Mother's Day.

As strong northwest winds pull the coldest air since April 8 over northeast Illinois, temperatures Saturday will likely fail to warm out of the 40s across the area and will be accompanied by wind chills in the upper 30s to lower 40s. Skies are expected to clear early in the evening, and as winds die off, temperatures will drop quickly into the 30s before midnight. During the early morning hours Sunday, the heat generated by the city will keep temperatures in the middle 30s, but in areas well away from the city, temperatures could drop to the freezing mark with resulting scattered frost.

Wet workweek

Temperatures begin to rebound under mostly sunny skies during the afternoon on Mother's Day, but highs in the upper 50s will still be almost 10 degrees below normal. Developing low pressure in the central Plains will move northeast, spreading showers and thunderstorms into Illinois on Monday night and continuing much of the day Tuesday. Preliminary indications are that after a brief break Wednesday, another storm system will bring showers and thunderstorms Thursday into Friday.

Dear Tom,
Your recent column about the meaning of percent chances of rain still has me wondering about it, so you have to spell it out for me. When the forecast says a 70 percent chance of rain and they are expecting up to 2 inches of rain, does that mean a 100 percent chance of rain but only a 70 percent chance of 2 inches?
--Randy Eagan

Dear Randy,
The proper interpretation of a 70 percent chance of rain (assuming the forecast verifies perfectly) is that you will have rain on your head 7 out of 10 times that you hear such a forecast. Probabilities of rain in weather forecasts do not address rainfall amounts -- only whether rain (at least 0.01 inch) will occur.
On occasion, forecasts might make mention of general rain totals ("locally heavy rainfall" or "light rain," for example), but rainfall probabilities refer only to the likelihood of rain, not to the amount.

Scott Jones of Evanston sends us this photo of a tree down near his home. In his words...

"I just watched the midday news and was listening to you describing the powerful winds that swept through our area during this morning's storms. I was home during the storms and heard this loud cracking sound as the winds really picked up at the end of the storm. I looked out the window and saw this mid-size elm tree come down over my neighbor's garage. Thankfully no one was hurt and no major damage to their garage as far as we can tell."
 
Thanks Scott for the report and photo, and give your neighbor our best wishes.

Wisconsin's Northwoods are bracing for up to 4" of wet snow while portions of the Dakotas dig out from under more than a half foot of the white stuff as a powerful spring storm moves across the Midwest. 

Thunderstorms spawned by the storm this morning produced .5" diameter hail near Bloomington and in Manteno, .75" diameter hail in Peotone, and nearly 1" diameter hail in Streator and Wilmington.

The Storm Prediction Center has placed our far southern suburbs and much of northern Indiana in a slight risk area for severe weather today. 

After the storm passes east of us this evening, colder Canadian air will wrap in on gusty west/northwest winds.  It will feel more like late March Saturday than early may with a high in the lower 50s.

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Thundery downpours sweep the area Friday---not all bad news with Spring 2010 the driest since 2001. And Friday's downpours aren't likely to be the last---though there will be a number of dry days between the waves of rainfall. A second and possible third rain and thunderstorm-generating system are targeting the area next week---the first due Monday night and expected to last into Wednesday morning and still another slated to arrive Thursday and Friday. Together, they could generate a seven-day tally between 2 and 3.50 inches---far more rain than the 1.88 inches which has fallen in the past month. 
   
Greatly reduced rainfall this year has taken a bite out of Great Lakes levels; each lake is down
 
The U. S. Army Corps of Engineers--which produces weekly reports on the Great Lakes---reports the dry weather is having an impact on the mammoth water bodies, home to 20 percent of the planet's fresh surface water. The water levels of each is down and, in the case of the eastern lakes, down dramatically from a year earlier. Lake Ontario has dropped a stunning 20 inches and Lake Erie is more than a foot (13 inches) lower. Lakes Huron and Michigan are 7 inches lower.

With each inch on Lake Michigan equal to an estimated 390-billion gallons of water, an estimated 2.73-trillion fewer gallons of water reside in Lake Michigan compared to a year ago.

It's not that rains have been absent this spring---they've just been lighter and less frequent than a year ago. The past 30 days have managed only 1.88 inches of rain which has fallen on eight days. The same period a year ago produced 5.38 inches on 14 days---roughly three times the moisture in twice the days.

It doesn't take long for topsoil to dry out this time of year. An average of 4.75 inches of moisture evaporates back into the atmosphere between April 8 and May 8. In a perfect world, that's the amount of rain which would fall over that period in order to keep up with the moisture loss. That hasn't come close to happening this year.
 
Wetter pattern in the cards
 
We may turn the corner on spring rainfall over the next two weeks if a succession of computer model predictions of much higher rainfall prove accurate. Rainfall projections extending past mid May boost rainfall substantially, predicting 14-day Chicago totals ranging from 2.44 to as much as 4.11 inches between now and May 20---a period in which 1.50 inches is considered normal.
 
Country's hottest air of 2010 bakes west Texas amid wind, bone-dry humidities
 
An extraordinary range in weather occurred across the U.S. Thursday setting the stage for Friday's thundery Chicago area downpours. As powerful westerly winds gusted to 40 mph amid single digit relative humidities out into the Plains of western Texas, Oklahoma and Kansas, snow loomed for northern Wisconsin and portions of the U.P.

Thursday temperatures topped 100-degrees at Pecos (104), Wink (101), Del Rio (101) and Midland (100)---all in west Texas---while snowfall at the 7,850 ft. level in Cole Creek, Montana hit 33 inches. Four inches accumulated at Bowman, North Dakota. 
 
 
A 3 inches or greater snow in Marquette, Michigan would be city's largest May snow in 20 years
 
Several inches of snow are likely to fall in portions of the Upper Midwest--most notably northern Wisconsin and Michigan's UP--potentially this spring's biggest snowfall there despite the late date on the calendar. Were 3 inches of snow to accumulate at Marquette, Michigan, the storm would become that area's biggest in May of the past 20 years.
 
 

Dear Tom,
Our rash of 80s this spring has given me hope for some 100s this summer. How long has it been since Chicago has had a 100-degree day?
--Ron Wilkens

Dear Ron,
It's been almost five years since the city last baked in triple-digit heat -- July 24, 2005, when the mercury peaked at 102 degrees at the official site at O'Hare International Airport and also at the lakefront, making for a very uncomfortable Lollapalooza concert in Grant Park. It was even hotter at Midway Airport, which reached 104 degrees.

That lone 100-degree day is the city's only occurrence since July 30, 1999, when the mercury reached 101.

Since Chicago weather records began in 1871 the city has recorded 61 days of 100 degrees or higher with the hot, drought summer of 1988 featuring the most, seven.

Frank Martin from Calumet City sent us these pictures of a recent fishing trip cut short by approaching inclement weather---but not before they made a great catch. Frank tells us he caught some nice trout.

Great pictures Franks. Thanks!!

We can't wait for everyone to meet Extreme-Weather Photographer Jim Reed, the Illinois native who's been chasing hurricanes and tornadoes for 20 years and who will be our guide for next week's Tom Skilling storm chase. Jim just told us by phone that Monday looks like a "really banner day."  We'll be "live" in Wichita, Kansas Sunday night at 9pm and chasing in southwest Kansas on Monday.

The Chicago area has received just half the meteorological spring rain that fell a year ago---5.60 inches since March 1 versus 11.08 inches during the same period in 2009. The dry weather combined Wednesday with powerful 30+ mph wind gusts and relative humidities in free-fall---they dropped from 59 percent at 8 am to 18 percent at 5 p.m.---elevated the risk that a wildfire might spring up and spread. That didn't happen, but fears it MIGHT prompted the issuance of a Red Flag Warning by the National Weather Service in the afternoon and evening hours. A series of small brush fires have occurred in parts of the area in recent weeks---several responsible for brief road closures, mainly in the northwest suburbs.

This spring's modest rains have permitted area farmers to complete corn planting as early as many can remember while,  at the same time, taking a toll on lake levels, which only in recent years had begun rising. Lake levels are now falling again---down a half foot from year ago levels.

But there could be a break in the dry weather  ahead. The drier than normal pattern may be growing tired. That's the suggestion of a suite of two week computer rainfall projections. The coming  14-day period (through Wednesday, May 19) is predicted to produce of 2.79 inches of  rain---far more than the 1.50 inches considered normal for the period. Of the eight most recent 2-week computer estimates, rain tallies range from 1.64 to 3.53-inches---each above normal!
   
Portions of the Chicago area could be in for the month's second 0.50+ inch
rainfall Thursday night into Friday
 
Rainfall is rarely evenly distributed in the year's warm months. The involvement of thunderstorms is a big part of the reason. Thunderstorms concentrate rainfall, producing downpours at one location while much lighter rains fall at another. There's NO compelling reason to believe Thursday night and Friday's system will be any different. The first in what could a series of rainy spells in coming weeks could be going here by the predawn hours of Friday--then continue amid strengthening winds into the morning. Rains are then likely to ease to sporadic sprinkles or end at times all together. Predictions of rain accumulations from this first wet storm range from 0.33 to as much as 1.53 inches while an average of all rainfall estimates with the system come out to 0.68 inches.

To date, spring 2010 has produced four 0.50-inch+ rains compared to 11 a year ago.
 
Pollen counts reach year's highest levels
 
A combination of dry weather, emerging vegetation and strong winds sent pollen counts soaring Wednesday. The values, according to Gottlieb Hospital and Dr. Joseph Leija, were the highest of 2010. Tree and grass pollen came in at "high" as did mold spores. Weed pollen was "moderate."
 
Late season snows could whiten northern Wisconsin, Upper Michigan
 
Amazing as it may seem, snow could whiten the ground in sections of northern Wisconsin and Upper Michigan later Friday and Friday night. Advisories for late season snow were issued late Wednesday across six states from Washington, Idaho and Montana into the western Dakotas---and may need to be expanded eastward.

Among the areas in which snow may stick is Rhinelander, Wis. and the Marquette area of Michigan¹s UP where snowfall this spring has amounted to just 0.1 inches. The incoming system, despite the late date, could produce the most significant snowfall there of this season.
 

Dear Tom,
I enjoy hot temperatures. How many days per year does Chicago hit 90 degrees or higher?
--Allen Samal
Dear Allen,
The annual frequency of 90-degree days varies considerably across the Chicago area, depending on the proximity to Lake Michigan and proximity to the most urbanized central core of the city. The former greatly reduces the annual occurrence of hot days and the latter greatly increases it, but it's complex because the two areas partially overlap. The lake lowers daytime temperatures in the warm season and the annual number of 90-degree days within about a half-mile of the lakefront averages eight. A couple of miles inland, it's 16 days; a few more miles inland (at Midway Airport, for example), it's 23 days. Farther away, say 10 to 15 miles inland, the frequency diminishes to 16 days (O'Hare International Airport).

Vortex2 kicked off possibly the biggest tornado chase in history this past weekend.  The $10 million dollar tornado study funded by The National Science Foundation and NOAA has 40 science and support vehicles at the ready.  Among those vehicles are "mobile mesonets".  They will get critical data at the surface including temperature, pressure, relative humidity and wind information.  Scientists hope to get a close look at  RFD's or rear flank downdrafts to see what part they play in triggering tornadoes.

To find out more about these mobile mesonets, check out the VORTEX2 blog.  Texas Tech University, North Carolina State University and Lyndon State College are also blogging their exploits as they join the hunt for twisters.

Today's prospects for severe weather are not that good.  The Storm Prediction Center doesn't even have a slight risk area posted anywhere across the United States.  If that should change though, the mobile mesonets and the doppler on wheels will be ready to roll.

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It's been nine years since as many 80s have been on the books this early in the season at Midway Airport. Tuesday's 80-degree high was the 6th of 2010---the most to occur by May 5 since 2001 when seven had occurred by now.

Warmer than average early season temperatures don't always offer clues on what the coming summer may hold.  Experimental seasonal temperature projections off a special breed of computer model which marries the atmosphere to the planet's oceans while attempting to take into account factors like soil moisture, have been hinting at below normal summer temperatures in the season ahead. Yet, it is interesting that just the opposite sort of warm-season temperature trends have followed seven of ten years since 1928 with similarly high early season 80-degree counts. In those years, temperatures ended up exceeding 90-degree an average of 26 days---more than the long term 82-year average of 23 at the South Side site. 

Last year---and in each of the past four years---90-degree tallies have ended up well below the 82-year average of 23 in the city. Last summer managed only 4 days with temperatures  of 90-degrees or higher at O'Hare and 7 such days at Midway.

Tornado touchdown reported late Tuesday in Wisconsin's Fox Valley north of Lake Winnebago
 
A tornado is reported to have "knocked a house down" in Winchester, Wisconsin around 7:15 p.m. Tuesday evening.  Winchester is a community southwest of Appleton in central Wisconsin. According to public reports received by the National Weather Service's Green Bay office, the twister was the by-product of an active group of late-day thunderstorms, some  with Doppler-scanned cloud tops as high as 44,000 feet.

The vigorous thunderstorms which spawned the touchdown had a history of funnel clouds and damaging 60 mph gusts as they raced through Wisconsin's Fox Valley area north of Lake Winnebago.

No equity in spring moisture distribution across the Nation's Heartland
 
With flood waters still out of their banks in sections of Tennessee Tuesday, after a monumental 17+ inch multi-day deluge which swamped sections of the Nashville area in the past week, it's interesting to note the huge disparity in spring rainfall over the nation's mid-section.

While Tennessee and other areas are still reeling from the effects of the cloud burst, a stubborn drought continues to  grip the upper Midwest, including northern Wisconsin and Upper Michigan. Small brush fires have erupted in parts of the drought zone in recent weeks.

Nashville's spring rainfall tally (since March 1) stands at 20.57 inches while over the same period, Rhinelander, Wisconsin and Marquette, Michigan have seen just 2.07 inches and 1.94 inches respectively---amounts a third to one half the normals of 4.36 inches and 6.24 inches. 

The 6-inch drop in Lake Michigan's water level (compared to a year ago) reported late last week by the U.S. Army Corps of Engineers, is due in part to lackluster rainfall over much of the Upper Midwest.
 

Winds ease over expanding oil slick
 
Even as fears emerge that the rate at which oil is flowing into the Gulf may have be been underestimated, calmer winds aided those trying desperately to stem the spread and landfall of the huge and growing oil slick in the Gulf of Mexico Tuesday. The arrival of more easterly winds over the coming weekend could encourage the oil to spread westward in the Gulf.

Dear Tom,
What is the latest date for an official 32 degree low in Chicago?
---Brigid Callahan

Dear Brigid,
The date of Chicago's latest official freeze is still several weeks away having occurred on May 25, 1992 when the thermometer at O'Hare International Airport dipped to 32 degrees. That month featured a prolonged late-month cold snap with daily low temperature readings in the 30s occurring from May 24 to 29, including back-to-back 33-degree lows May 27 and 28. That cool spell set the tone for a very cool summer that featured only six days in the 90s, a result of widespread haze and volcanic debris thrust into the stratosphere from the June 1991 eruption of Mt. Pinatubo in the Philippines.
Looking ahead, the city's freeze-free season extends to Sept. 22, the date of the earliest fall freeze when temperatures dropped to 32 degrees in 1995.

Spring 2010 among the 7 warmest in 140 years here
 
The weather of spring 2010, which moves into its 65th day Tuesday, has propelled the season into rare climatological territory. Its production of 70-degree days--there have been 15 of them since March 1 (10 days are average and only eight had occurred by this date a year ago)---places it among only 9 percent of springs which have done so. Its 48.7-degrees average has not only topped last spring's rain-plagued temperatures by 4.8-degrees, it's left the long-term average behind by 5.9-degrees.  

The season's rainfall story is every bit as compelling. Rainfall to date has run 16 percent behind the long term average: 5.60 inches to-date in 2010 versus the 6.67 inch tally considered "normal". But the comparison with last year's waterlogged total is most striking. The season has seen just over half last year's 10.47 inches.  That means you would have to double this spring's rainfall just to equal the moisture levels of a year ago.


Farmers have taken advantage of the season's limited rainfall
 
The effect of this spring's dry, mild weather has been most evident on the region's farms. The weekly crop-progress report from the U.S. Department of Agriculture was released Monday and indicates Illinois farmers have 87 percent of this year's corn crop in the ground, more than 17 times last season's 5 percent. While the report deals with averages, the reality across many sections of the state is that corn planting is now complete and farmers have moved on to planting the 2010 soybean crop.

That work---and all other outdoor activities---will proceed unimpeded Tuesday. Mild, windy weather, with powerful west to southwest wind gusts expected to top 30 m.p.h. by afternoon, are predicted to propel temperatures well into the 70s---to within striking distance of 80. A few thunderstorms may arrive in the pre-dawn hours of Wednesday, but coverage on these storms is likely to be limited to just 20 to 40 percent of the metro area.

Cooler, wetter pattern looming?

A cooler, wetter overall pattern may be in the offing beginning later this week and in the week which follows. That doesn't mean it will rain continuously--far from it. But it does mean rainfall over the next two weeks might well total more than the 1.56 inches considered normal for the period.  All six of the most recent runs of the National Weather Service's "GFS" (Global Forecast System model) produce 14-day Chicago rainfall totals  well above normal---averaging 2.77 inches through Monday, May 17. The increased cloud cover during that period may act to restrain temperatures, producing a cooler overall regime.


Mays often turn cooler following similarly warm springs to date


A review of Chicago weather records reveals it's not unprecedented that May's pattern would take a turn in the wake of a warm, dry spring open. Seven of 8 years which have followed mild spring opens---88 percent of them---have gone on to experience below normal overall May temperatures. But, warm weather enthusiasts shouldn't fret---at least not at this point. A majority of the summers which have followed in these years---5 of 8 of them---have displayed overall summer temperatures which have finished above historic norms.

Late week storm system could bring 0.50 to 1-inch rains
 
There are indications a blustery wet late week storm is to make its way into the Midwest. The system, predicted to sink from Colorado south to Oklahoma Thursday then to hook northeastward, crossing central Illinois and Indiana, appears likely to tap sufficient Gulf moisture that it could begin producing rains here---possibly with some embedded thunderstorms---late Thursday night into Friday.  A second comparable system can't be ruled out Monday night and Tuesday of next week.

Dear Tom,
I remember a flood in Chicago in late August 2001. Can you provide information on this event?
--Maria Kursk, Chicago

Dear Maria,
You are remembering the major flash flood that struck Chicago during late evening Aug. 30, 2001. The deluge targeted area from the Northwest Side to Wisconsin with torrential rains in excess of 4 inches. Major flooding shut down portions of the Edens Expressway where water was 10 feet deep near Pratt Avenue. The heavy rains also flooded basements and viaducts throughout the area and thousands lost power in the northwest suburbs. This flood was actually the area's second of the month as major flooding occurred in a 30-mile wide corridor from Lake County south through Chicago to Kankakee early in the morning on Aug. 2. August 2001 recorded 12.25 inches of rain making it the city's fourth wettest August on record.

Nashville is bracing for more flooding as the Cumberland River is expected to crest at 50 feet or ten feet above flood stage.  More than a foot of rain fell the over the weekend.   That is nearly three months of rain in just two days. According to the Nashville National Weather Service office the two-day rainfall total was 13.57" breaking the previous two-day record of just under 7 inches. 

Flooding may impact downtown Nashville and some tourist attractions including LP Field, where the Tennessee Titans play.

The death toll from the weekend flooding across Mississippi and Tennessee is at least 15.

The good news is Nashville should be relatively dry this week with the next good chance of rain there Friday.

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Showers and thunderstorms could develop here Monday afternoon as a frontal system approaches the city. With a pocket of cold air aloft creating a buoyant environment favorable for thunderstorm development, the storms could become severe.

Similar conditions Sunday produced wind gusts to 75 mph at Des Moines and 71 mph at Marshalltown -- both in central Iowa -- while 1-inch-diameter hail fell in portions of Missouri and Kansas.

A brief warm-up will send temperatures well into the 70s Tuesday and Wednesday before a late-week storm system ushers in cooler weather that could bring a chilly Mother's Day weekend to the area.

Dear Tom,
Your Sunday column mentioned how it has snowed only once in June in Chicago back in 1910. In June 1969 I was south of the Twin Cities, and it snowed all day. What day was that, and what happened in Chicago?
-- Douglas Hanbury, East Peoria

Dear Douglas,
That unseasonably cold day when snow fell across much of Minnesota was June 2, 1969. Most of the snow melted as it fell, but accumulations up to an inch were common in the northern portions of the state. That June turned out to be Minnesota's coldest on record with many instances of frost, below-freezing temperatures and record lows in addition to the rare June snowfall. Though it was significantly warmer in Chicago during that period, it was no picnic here either. Light showers fell on June 2 with a high of 60 degrees and a low of 48. It was cloudy and even colder the next day with a high of just 57 and a low of 41.

Jeff, Beth and Zack Maaske sent us these photos and this report from Nashville.

Greetings from Nashville! We have had 10-plus inches of rain since 7 a.m. Saturday!   The Cumberland River in Nashville went from 21 feet Saturday at 10 a.m. to 42 feet Sunday at 10 a.m.! 

Pictures below are from our subdivision, a water rescue in Brentwood, Tenn., and our CoCoRahs gauge.  That gauge holds 11 inches and it's almost full!

Thanks Jeff, Beth and Zack!

A surge of cloudiness  overspread  the Chicago area Saturday afternoon putting a lid on temperatures that kept highs to only around 70, a drop of about 10 degrees from Friday's summery round of lower  80s, the fifth recorded during the city's third warmest April on record. The clouds were the forerunners of a  disturbance slated to bring some showers and thunderstorms to the area Saturday night into Sunday morning. After several days  with highs near 70  gusty southwest  winds should bring a return of near 80 degree warmth to the area by midweek. Beyond that, another cool down will send temperatures tumbling back to the seasonable 60s by week's end setting the stage for what could be a rather cool Mother's day weekend with high temperatures struggling to reach 60 degrees.
 
Two  twisters confirmed in Wisconsin Friday night
A National Weather Service storm survey Saturday confirmed two EF-0 tornadoes struck near Glen Oak in south central Wisconsin north of Madison during Friday's severe weather episode. Top winds were estimated at 70 mph with mainly tree damage reported along the 8 mile long damage paths.
 

Dear Tom,
My aunt told me that it snowed in June sometime in the '90s. Can you provide any details?
--Hazma Hussain, Willowbrook

Dear Hazma,
The only detail that we can provide is that it didn't happen. Since the start of the city's snow records in 1884-85, snow has been recorded only once in June and that was on June 2, 1910. It was a chilly day with a high of 55 and a low of 43 and a thunderstorm (probably during the early morning hours) brought a mixture of rain, hail, and snow pellets. Rainfall that day totaled 0.41 inches and snowfall was recorded as a trace (an amount too small to measure). Other than that lone June event, the city's latest-occurring snowflakes were traces on May 25, 1924, and May 26, 1889. Chicago's latest-in-the-season measurable snow took place May 11, 1966, when 0.2 inches of snow was recorded.