WGN-TV Chief Meteorologist Tom Skilling and the WGN Weather Center staff provide daily coverage of weather in the Chicago area.

May 2009 Archives

Just wait, and the weather will change over the metro area today. A cold
front will move through northeast Illinois preceded by showers and
thunderstorms. Strong storms with localized heavy downpours will pass to the
north this morning, and then a more organized band of showers and
thunderstorms should develop along the frontal boundary as it moves south
through the area this afternoon. Behind the front, winds shift to the
northeast bringing much cooler air off the 50-degree surface of Lake
Michigan. Further to the south ahead of the front, strong, possibly severe
storms will develop in moisture-laden 80-degree air.

More rain Tuesday

The cold front will become stationary south of Interstate 80 Tuesday with
resultant showers and thunderstorms likely to produce additional heavy rains
and possible flooding over northern Illinois. A slight shift in the jet
stream should move this weather system well to the south Wednesday, allowing
a drying-out period the rest of the workweek. Showers and thunderstorms may
return to the Midwest this weekend.

Frost and freeze warnings in the Northeastern U.S. tonight

A very cool Canadian-source high pressure air mass will sit over the northeast tonight. With clearing skies and light winds, a late season frost/freeze is expected over a large portion of the northeastern U.S. as temperatures are forecast to drop into the lower 30s early Monday morning from Maine to northern Pennsylvania.

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Ideal air-conditioning settings

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Dear Tom,
The air conditioning season is here again, and my co-workers will be arguing about thermostat settings in the office. What are your thoughts about ideal temperatures?
Greg Bolick
Dear Greg,
Indoor comfort levels are a matter of personal preference, and our "internal thermostats" are all set slightly differently. Air temperature is a big factor, but relative humidity and air movement are important too.
We checked with acknowledged experts in the field of indoor environmental comfort: the 55,000-member American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), headquartered in Atlanta. An ASHRAE study determined that a temperature of 74 to 76 degrees in an office environment is comfortable for most sedentary people when the relative humidity is 50 to 60 percent and there is a slight air movement (but not strong enough to be a draft).

Icy groundcover in Rensselaer

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While the Chicago area was enjoying a sunny and warm late Saturday afternoon yesterday, strong hail-producing thuderstorms were lashing portions of  northwest Indiana. Thanks to Donna Wetzel for sharing this shot taken around 5:15 p.m. in downtown Rennselaer, Indiana. Pea-sized hail covered the ground and 0.90 inches of rain fell in just a few minutes.

 

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Photo by Donna Wetzel

Arc de Triomphe in the clouds

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 Thanks to Jeff Maaske who took these great pictures last Wednesday in Brentwood,Tennessee. The cloud formations do indeed resemble the famed French monument.

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Photo_052709_002 [800x600] [640x480].jpg Photos by Jeff Maaske

A sunny Sunday, But storms return Monday

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High pressure over northeast Illinois Sunday will give mostly sunny skies,
scattered fair-weather cumulus clouds and mild temperatures. However, events
should change rapidly as clouds thicken overnight with the approach of a
cold front. As the front moves through Monday, warming will occur along with
showers and thunderstorms. Severe storms are possible later in the afternoon
and evening. Behind the front, northeast winds off Lake Michigan will bring
a sharp 10 to 20-degree temperature drop.

Widespread heavy rains possible

As the cold front slows and becomes nearly stationary just a little south of
I-80, atmospheric conditions will be ripe for heavy, potentially flooding
rains north of the front, if repetitive thunderstorms track over the same
areas Monday night and Tuesday.

The southern edge of cool Canadian high pressure should hold over the
Midwest and Great Lakes the remainder of the workweek ,however computer
models indicate low pressure will spread rain back into this area this
coming Saturday.


The composition of the Earth's atmosphere

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Extreme heat in Chicago--How often?

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Dear Mr. Skilling,
My teacher, Mrs. Denning, said Chicago sometimes gets very hot weather, and she said
it is a scorcher when it hits 100 degrees. How many days have been that hot, and what
is Chicago's hottest temperature?

---Ashley Jameson (5th grade)

Dear Ashley,

Few Chicagoans would disagree with Mrs. Denning when she calls a 100-degree day a scorcher. Since the start of Chicago's temperature records on Nov. 1, 1870,the city has had some real scorchers. Chicago has logged 61 days with temperatures of 100 degrees or higher, and the last time it happened was July 24, 2005, when it hit 102. Chicago's official highest temperature is 105(July 24, 1934), when the thermometer was at the University of Chicago. One day earlier it was 109 at Midway Airport, and that is Chicago's highest recognized, though unofficial, temperature. 

Shower or two may dampen a warm day

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There will be no repeat Saturday of Friday afternoon's lakeside temperature plunge that saw Wrigleyville readings drop to 55 degrees from 72 from noon to 2 p.m. That's because northwest winds will blow with sufficient strength to overcome the easterly lake breezes behind Friday's cooling.
Northwest winds aloft carried a showery disturbance over parts of the area late Friday. The thunderstorms that erupted with that system waited until passing the Chicago area to erupt. Cloud tops hit 43,000 feet in central Illinois.
Spotty showers will greet Chicagoans with a second disturbance Saturday morning, and a third wave may set off an isolated thunderstorm late Saturday.
Most of the weekend will remain dry.

Storms ahead
A strong cold front will move through northeast Illinois on Monday, triggering thunderstorms that may become severe in the afternoon to evening hours. Widespread rains between 1 and 2 inches are possible Monday night into Tuesday.

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Was it hot on June 21, 1950?

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Dear Tom,
I graduated high school in Chicago on June 21, 1950, in an outdoor ceremony
held on the school steps. I remember that it was so hot that some of the
girls didn't wear dresses under their robes. How hot did it get that day?

Ann Lee, Chicago
Dear Ann,
Your graduation day was probably not as hot as you remember, but it was warm
and rather humid with partly sunny skies. There were some showers, but
rainfall was light with most areas receiving nothing more than sprinkles.
Climatologist Frank Wachowski informed us that high temperatures across the
area that day were in the lower and middle 80s with dew points hovering in
the lower 60s. The city's official high  observed at Midway Airport was
85 degrees. The next few days were even warmer, reaching 88 and 90. It
probably felt hotter than it actually was because of the heat absorbed by
the school building.
Mark Vogan, our intrepid observer and chronicler of the weather of Scotland and the United Kingdom, sends us these beautiful shots of the region's first low 70-degree temperatures of 2009. Mark and Karen (as well as their little cat Mia) have just moved into a new home, which is included in several of these shots! Congratulations on your new home, Mark and Karen---and give Mia a friendly pat from all of her new friends across the Atlantic!





Photos courtesy of Mark Vogan, Glasgow, Scotland


Beautiful garden pictures from Winfield, Indiana

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Our good friend and amazing photographer Amanda Pickett e-mails to tell us she was busy in her garden this past Memorial Day weekend. She, her husband and daughter managed to get the whole thing planted!  Way to go Amanda! Check out these beautiful photos she has sent us from her garden in Winfield, Indiana. Let me share a few sentences of explanation from Amanda's e-mail:
 
"It's a lovely day here in Winfield.  I got the whole garden planted over the Memorial Day weekend (with my husband and daughter's help of course) and everything enjoyed the light rains we have had here.



Here is a photo of a money plant flower with morning dew in my garden.  These are the plants that create those silver dollar sized, transparent, shimmery seed pods in the fall. 



Also included is a bumblebee on an onion chive flower.  Always happy to see the bees!"




And we're always happy to hear from you and see your beautiful photos, Amanda!  Happy Friday to you and hope the weekend's a great one!
 
Photos courtesy of Amanda Pickett, Winfield, Indiana

Dan Giampaolo shares this rainbow photo with us. He tells us the rainbow appeared for about 10 minutes between 5 and 5:30 p.m. and that he photographed them above Redmond Park in Bensenville.  Great shot! Thanks Dan!



Photo courtesy of Dan Giampaolo, Bensenville, Illinois

Sun breaks through; warm weekend ahead

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The 13th and final weekend of meteorological spring is likely to be the season's warmest. And half of the season's copious rainfall -- 6.78 inches of the 14.02 measured at O'Hare International Airport since March 1 -- has occurred during the past 12 weekends.
After a series of cloudy days reduced temperatures in the Chicago area, the return of sunshine will boost readings Friday substantially. A light wind regime means daytime heating could encourage the cooler, denser air that hugs Lake Michigan's surface to ride into shoreline areas as a lake breeze Friday afternoon.

Think May's been cold? Last May was cooler

Chicagoans may be surprised to hear that May, which ends Sunday night, is actually running a bit warmer than normal. The month's 59.6-degree average temperature is 1.7 degrees above the 138 year long-term average and a full 5 degrees ahead of the same period a year ago.

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Rainy summer weekends

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Dear Tom,
Living in Chicago during the summer of 1969 I seem to remember that it rained nearly every weekend. Am I correct?

-Mike Becker
 
Dear Mike,
Your question intrigued us and after checking it out with the help of Chicago climatologist Frank Wachowski we found that you are absolutely correct. Some rain was recorded on an astounding 11 of the 14 weekends (79 percent) of meteorological summer (June, July, August) in 1969---and 6 of those 11 weekends recorded rain on both days. Every weekend in June and July logged at least one rainy day. Only August brought some relief from the rainy weekend syndrome with three dry weekends and two having only one day with rain.

That summer's two rainiest weekends were June 7 and 8 when 2.10 inches fell and July 26 and 27 with 1.59 inches.
 

Crepuscular rays late Thursday evening over Chicago

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Colden Searles share this photograph taken late Thursday which shows crepuscular rays of sunlight emanating from breaks in the days persistent overcast.  Thanks Colden!!
 
Tom Skilling
 

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Photo Courtesy of Colden M. Searles, Chicago


Midway soaks in its wettest spring since '28

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It's not that rainfall has occurred more frequently than usual since March 1. (The three-month March-through-May meteorological spring period receives an average of 49 days of rain in the 139 years of official Chicago weather records dating back to 1871.) But this spring's 44 days of rain to date have actually fallen five days short of the long-term benchmark.

 But when is has rained here, rainfalls have been impressive. And that's led to one of this city's wettest springs on record. O'Hare International Airport's 14.01 inches of rain since March 1 ranks as the fifth wettest of the past 139 years. But Midway's 17.04 inches exceeds any March 1 to May 28 period since records began at the Southwest Side airport in 1928.

With the clock ticking on 2009's meteorological spring season-only four days remain until its close at midnight Sunday-many Chicagoans wonder if the wet spring offers clues on the summer ahead.
Weather records indicate a modest tendency toward a cooler and wetter than normal and wetter than normal meteorological summer period.
click image to enlarge

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Reliability of 7-16 day-range weather forecasts

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Dear Tom,
We're planning a big graduation party for June 6 or 13, preferably outdoors.
What is the weather likely to be?

Michael Krainas

Dear Michael
The ability to reliably predict details of the weather beyond seven days diminishes rapidly. Forecasts in the 7 to 16 day range are best at offering general insights into the weather pattern likely to prevail, such as the probable orientation of the weather-steering jet stream or the trend in precipitation. Weather forecasts, as we move into summer, become especially tricky because of thunderstorms. These storms can be notoriously troublesome for forecasters because of the cool outflow of air they produce which all too often alters other features of the large scale weather pattern. Because thunderstorms can be short-lived and comparatively small, predicting the specifics of their evolution is difficult at longer time ranges.

Climatologically, the chance of rain on any given day during the first half of June is one in three. Bear in mind, though, that a thunderstorm usually passes in an hour or two, and rarely is a thundery day a total washout. Even on a "rainy" summer day, most of the hours are rain-free.
 

Slow-moving system brings soaking rains

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Flooding downpours hit sections of the Chicago area with clusters of
slow-moving thunderstorms late Tuesday. Radar scans indicated cloud tops
over 40,000-feet tall.

   The weather system responsible was the same one that flooded sections
of Florida with more two feet of rain last week. Its northward jog
across Illinois generated 10.50 inches of rain in Downstate
Edwardsville, northeast of St. Louis, on Monday.

  By late Tuesday, rainfall totals in the Chicago area had passed 2.50
inches at Joliet with more than 2 inches measured in Plainfield and more
than 1 inch at Oak Brook and Midway Airport.

Wet spring at Midway

  The recent downpours have helped push the rainfall tally since March 1
(the start of meteorological spring) to more than 16 inches at the
Southwest Side site, wettest of any such period on record since 1928.
click image to enlarge
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Days of precipitation in Chicago

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Dear Mr. Skilling,
We are studying weather and I want to ask you how many days in a year we have precipitation. How many days do we have heavy precipitation?

-Robert, Wilmette

Dear Robert,
The Chicago area receives precipitation (like rain, snow, drizzle and sleet) quite often. That comes as no surprise, considering that far above-normal precipitation has been drenching us since last summer. In 138 years (1871 through 2008, or 50,404 days) measurable precipitation (0.01 inch or more) has fallen on 17,153 days, or an average of 124 days per year. In addition, a trace of precipitation (an amount too small to measure, like just a few drops of rain or a few flakes of snow) has fallen on 8,292 days, or 60 days per year. On average, at least some precipitation (trace or measurable) falls on 184 days, or half of the year's 365 days. Heavy precipitation (1.00 inch or more) arrives on seven days per year.
 
Photographed in the Gary area by Carolyn Szepanski. 

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Check out another beautiful shot of Sunday's eye-catching sunset as photographed from Manteno, Illinois by Carole Fortenberry! THANKS for sharing this with us Carole--it's a beauty!
 
-Tom Skilling

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Photo courtesy of Carole Fortenberry, Manteno, Illinois

Many thanks to Carolyn Szepanski of Whiting, Illinois for this shot of Sunday's beautiful sunset.  Carolyn has shared many beautiful shots with us over the years! 
 
-Tom Skilling

 
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Photo courtesy of Carolyn Szepanski, Whiting, Indiana
This late afternoon shot of a towering thunderhead (cumulonimbus cloud) near Springfield illustrates the vertical growth which took place in Tuesday's northbound thunderstorms.  Anson tells us he had to fly through a line of storms there--but did so successfully.  Great shots, Anson!  Thanks for sharing them with us.
 

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The thunderstorms, predicted to continue sweeping the Chicago area in clusters, are shown here developing near Peoria. Our friend and pilot Anson Mount took the photo below at the 28,000 ft. level this morning as he was en route to Alton. The cell pictured here forced Anson to fly around it.  It's so interesting to look at the storms behind the heavy downpours, which have hit sections of the state with the tropical weather system now lifting northward from Missouri, from another perspective.  THANKS Anson!  Another great shot!
 
-Tom Skilling

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Photo courtesy of Anson Mount, Algonquin, Illinois


Slow moving storms threaten Chicago area

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The same humid tropical air responsible for more than 2 feet of rain and waves of thunderstorms across sections of Florida last week has made its way to Chicago.
That this air mass is of tropical origin isn't immediately apparent because of winds off a still chilly Lake Michigan, but its moisture content is bountiful. Nearly 2 inches of water is evaporated in a column of air over Chicago -- moisture that is available to be swept into the concentrated downpours of thunderstorms expected to build this afternoon and evening as daytime warming takes place. Converging surface winds along a northbound warm front threaten to enhance the upward motion of air later in the day and into the night. Further complicating the potential for heavy rains are the light winds stacked high in the atmosphere above Chicago. At jet stream levels -- from 18,000 to 40,000 feet where winds can reach 80 m.p.h. or more this time of year -- winds Tuesday should hover near 20 m.p.h. This will slow the forward movement of any thunderstorms that erupt, prolonging downpours at the hardest-hit locations.
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Fata Morgana

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Dear Tom,
Standing on a 75-foot-high bluff just south of Saugatuck, Mich., we saw what appeared to be the Milwaukee skyline across Lake Michigan. Was it a "Fata Morgana" type of mirage?
Bonnie Wheaton
Dear Bonnie,
What you saw was a "superior mirage" sometimes called a Fata Morgana, caused by a temperature inversion with a layer of cold, dense air over the lake and warmer air above. The inversion bends the light rays from the city, creating stretched or "towering" images sometimes resembling bar codes back down towards the chilled air near the lake's surface. Fata Morgana is Italian for Morgan the fairy, a mythical character that supposedly lived in a crystal palace beneath the waves. The name came from the fairylike castle mirages that frequently appear over the Strait of Messina separating Sicily and Italy.

Duffinately Weather

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Today Monday May 25th 2009 we had a high of 67 degrees which occurred at 11:21 am with overcast mid level clouds and a cool east wind coming off of Lake Michigan, (water temp 58 degrees)

Here are some Memorial Day statistics comprises 136 years of data.

Memorial Day isn't a set day so their are no average High temps...Most frequent high temps are between 70-79 degrees.

Warmest Memorial Day was May 30th 1942   H: 93 degrees

Coldest Memorial Day was May 30th 1889 H: 42 degrees

Last year May 26th 2008 the High temperature was 81 degrees

54 % of the time it doesn't rain on Memorial Day but 56 % of the time it does:(

The most frequent range is .02" - .25" of rain

The most amount of rain ever was an 1.00" on May 28th 1984

Last year (2008) .48" of rain fell.

Coolest Memorial Day since '04 likely dry

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Gathering clouds and winds off chilly Lake Michigan will suppress temperatures Monday, keeping readings mainly in the 60s with areas along the immediate lakefront hard-pressed to break 60 degrees. In 2004, it reached 66 degrees.

Most of this holiday should be dry, but showers could reach southern parts of the Chicago area by nightfall. It's all downhill from there as a sluggish low pressure system takes up residence across the Midwest, bringing the city a rainy period that could last into Thursday. This system brought upward of 2 feet of rain to Florida last week and continues to produce impressive rainfall totals. The Little Rock area received more than 2 inches of rain Sunday, and nearly 3 inches doused Lake Charles, La. Flash flooding occurred in northeast Arkansas, and twisters were sighted in northwest Tennessee and southeast Missouri.

Twister hit 113 years ago
On May 25, 1896, an F3 tornado did considerable damage as it cut a 4.5-mile path from Park Ridge to Niles. Areas in Edison Park and Norwood Park were hit hard.
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Warm and cool Memorial Days

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Dear Tom,
How often has it been 90 degrees or higher on Memorial Day? Has the temperature ever failed to reach 70 degrees?

Nick Recchia, River Grove

Dear Nick,
Memorial Day, originally known as Decoration Day, is a national day of remembrance of U.S. men and women who died while in military service. Until 1970, Memorial Day was always observed on May 30, but since 1971 it has been observed on the last Monday of May (and the date varies from May 25 through May 31).

On average, the Memorial Day temperature climbs to 90 degrees or higher on one day out of eight. However, Lake Michigan, whose water temperature off Chicago is often in the 40s in late May, greatly reduces the occurrence of 90-degree days to about one in 70 at the lakeshore. High temperatures fail to reach 70 degrees quite often: one day in three inland, and one day in two at the lakeshore.

Slow-moving storm to bring cool, wet week

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Chicago's brief respite from cool, wet weather is over as a storm system
that drenched Florida with upward of two feet of rain the past few days
takes aim at the Midwest. Cloudiness will begin to roll in late Sunday,
setting the stage for a prolonged cool, wet period that will last into
Thursday as the storm works its way into the Midwest via a trek through  the
Gulf States and the Missouri and Mississippi Valleys. During this period,
temperatures in the city and near the lake will be hard-pressed to get out
of the 60s as clouds, rain and winds off the lake all combine to promote the
cool conditions.

City could get a soaking

This storm continues to produce heavy rain and the Chicago area could see
significant totals midweek. West Palm Beach, Florida was inundated by a
daily record 5.33 inches Saturday while Daytona Beach logged 2.56 inches.
Flash flood watches are posted for portions of Mississippi and Arkansas for
up to four inches of rain. The storm also spawned a possible twister in east
central Alabama at Halawaka Creek Saturday damaging docks and overturning
several boats.
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Hurricanes in California

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Dear Tom,
Why aren't there hurricanes in California if it is by an ocean?

-Ellen Szostak, age 10

Dear Ellen,

The reason why California doesn't get many hurricanes is because the ocean water there is just too cold. Tropical cyclones generally need a water temperature of 80 degrees or higher for formation, and the waters off the California coast usually range from the middle 70s in the far south portion of the state to the very chilly upper 40s near the Oregon border. The eastern Pacific Ocean gets its share of hurricanes, but most develop in the warmer tropical waters from Central America north to Baja California. These storms sometimes strike the west coast of Mexico, but most tend to move west into the open Pacific and dissipate. On rare occasions, one of these storms will move north and affect the southwestern United States.

Chance of rain in the air for Chicago area

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Rain isn't completely out the picture Saturday, but dry hours will
outnumber any wet ones. Saturday afternoon's air is to hold 1.25 inches
of evaporated water and the day's initially light winds are unlikely to
flood the area with cool, stabilizing air off the lake.

With mixed sunshine predicted and a slightly faster than usual vertical
decline in temperature -- a condition which encourages air to rise and
cool, thereby producing clouds -- the potential exists for scattered shower
and thunderstorm development. Computer models are predicting a column of
the atmosphere above Chicago may grow saturated later Saturday with
moisture to an altitude of more than 30,000 feet, suggesting vertical
clouds capable of producing some thunderstorms.
 
Winds converging along a weak southeast-bound front may further
encourage precipitation development, though peak areal coverage isn't
likely to exceed 20 to 30 percent of the metropolitan area.

Lake winds strengthen Sunday, sweeping modestly cooler, drier air across
the area and reducing the chance of rain.
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Understanding 'degree day units'

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Dear Tom,
I often hear the term "degree day units" and it has me stumped. What are
they and what do they mean?

Mike Matuk
Dear Mike,
Heating and cooling degree days are measures that indicate the departure of
a day's average temperature from 65 degrees. When the average temperature
(sum of the high and low divided by two) equals 65, engineers have
determined that neither heating nor cooling is needed to maintain a
comfortable indoor environment. When the day's average temperature is above
65, each degree of departure is one cooling degree day (CDD) and when below
65 one heating degree day (HDD). Running totals are kept for both HDD and
CDD giving a quick one-number snapshot to compare seasonal heating and
cooling costs. The HDD season runs from July 1-June 30 to capture the entire
heating season while CDD totals are kept on a calendar year basis.

Photos from rain-soaked Florida

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Check out these Florida photos taken Sunday as the current deluge-generating system was getting under way!
 
Florida rainfall over the past week (through Friday evening  May 22) reached 28.00" (since Sunday) at Bunnell (in Flagler County), 19.90" Daytona Beach, 10.44" Orlando, 7.62" Melbourne and 6.30" at Vero Beach. Greg Jakubowski was in the Sunshine State as the first stage of the current downpour-producing weather system was moving in.  Greg took these photos earlier this week and shares them with us.  In the e-mail which accompanied these shots, he tells us:
 
"I returned late Tuesday from visiting a daughter who lives about 40 miles southwest of Tallahassee, Florida. On Sunday, May 17, we were in the St. George Island / Apalachicola area.
 
I thought you might we interested in some cloud pictures."

We are indeed--THANKS for sharing these with us Greg!



This first one was taken looking more or less north from St. George Island.



I took this one right in the middle of dinner at a restaurant on the Apalachicola River.

The storm was moving north to south. It didn't produce lighting until it after it was over the ocean.


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This one was taken right at the mouth of the Apalachicola River.



This last one is the Apalachicola River bridge. Clouds aren't that exciting but I like the reflection on the water.

Photos courtesy of Greg Jakubowski, Schaumburg, Illinois

Sign of spring: Bluebirds

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Mike Zarnek was kind enough to send in this wonderful shot, taken earlier this month, of a bluebird at Ryerson Woods near Deerfield. Thanks Mike for sharing your photo!

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Photo courtesy of Mike Zarnek, Mount Prospect

3 days of warmth and sunshine come to an end

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Three consecutive days of 80s-the longest warm spell in the Chicago area
since last September-come to an end. Northeast winds and noticeably
cooler temperatures greet area residents as Friday gets under way.

A southbound cold front swept in around 8 p.m. Thursday bringing an end
to the warmth that included a second 84-degree high at O'Hare
International Airport and an 85-degree peak reading at Midway Airport
earlier in the day. The influx of cool air saturated the lower
atmosphere with moisture and is behind the cloudiness and sprinkles in
place early Friday.

Not only did temperatures plunge, the frontal passage brought an end to
Chicago's string of three days with 100 percent of the area's possible
sunshine-the longest such spell here since October 29-31.

Big rain tallies in Florida

Since Sunday, 17.21 inches was tallied at Daytona Beach, 13.31 inches
in the Sanford/Orlando area and 24.78 inches in the Ormond Beach area
just north of Daytona Beach.

click image to enlarge
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Is there such a thing as lake-effect rain?

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Dear Tom,
Is there such a thing as lake-effect rain?

John Lustrup Glen Ellyn

Dear John,
While we most often hear about lake-effect snow, lake-effect rain does occur
over Lake Michigan and the other Great Lakes, but is it a rare phenomenon
usually seen in autumn. In order for lake-effect precipitation to form, the
temperature of the air about a mile above the lake surface must be at least
20-25 degrees colder than the water. That magnitude of temperature
differential is seldom realized in summer so we rarely experience
lake-effect rain. When these conditions do occur, they are frequently in
conjunction with potent early autumn cold outbreaks packing air sufficiently
chilly to generate lake-effect rain.  The very cold air over the warm lake
creates a very unstable atmosphere and the lake-effect rain is often
accompanied by thunder and lightning.


Here's a sign of spring: 4 robins hatch!

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Jennifer and Willy Mendez send along this photo of 4 newly hatched robins.  It was taken the day before yesterday by Matthew Weglewski with the birds just 5 days old!  The newborns offer us yet another sign we are well into spring!  Please thank Matthew for the great shot, Jennifer and Willy!

Thanks for sharing this with us!
 
Tom Skilling

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Photo from Jennifer and Willy Mendez and taken by Matthew Weglewski

Chicago's warm spell good for a 3rd day

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Chicago-area residents can look forward to a third consecutive day in
the 80s on Thursday. The unseasonable warmth follows Wednesday's
84-degree high at O'Hare International Airport and 85 at Midway-tying
2009's highest readings to date. Temperatures as warm as 88 degrees
occurred at Wheaton and 86 at Flossmoor, but surged into the 90s a
second day in Minneapolis, eclipsing the previous record of 91 dating to
1975.

The warm spell comes to an end with the passage of a wind-shifting cold
front Thursday night. The easterly winds predicted behind the front in
coming days will temper daytime warming, especially near Lake Michigan.

Rains continue in Florida

By late Wednesday, Bunnell, in Flagler County, had tallied 23.75 inches
of rain since Sunday. Rainfall on Wednesday alone totaled 9.27 inches at
Jacksonville Naval Air Station and 6.74 inches at Daytona Beach. The
moisture producing those rains is to sweep into the Midwest encouraging
holiday weekend haze and cloud development.
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Chicago's longest string of 100-degree days

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Dear Tom,
What is the largest number of consecutive 100-degree days we have ever had
in Chicago?

Paul Sarewich, Chicago

Dear Paul,
In official temperature records dating from 1871, Chicago has logged three
consecutive 100-degree days on two occasions: July 3-5, 1911 (100, 102, 102
respectively) and August 4-6, 1947 (100, 100, 101). Those are Chicago's
longest strings of 100-degree days, but they are hardly a true
representation of the blistering heat that has occurred in the city.
Chicago's official thermometers were sited near Lake Michigan (in the Loop
or at the University of Chicago) from 1871 to 1942 and stifling heat waves
during that period were blunted by the city's well-known lake breezes. Data
from Midway Airport tell the real story. Eight consecutive days of
100-degree temperatures roasted the city on July 7-14, 1936: 102, 106, 100,
106, 107, 100, 102 and 104.

Warmest day arriving on gusty south winds

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Temperatures in the Chicago area are to surge to their highest levels of
2009, peaking within striking distance of 90 degrees in the area's
warmest locations. The summer-level temperatures arrive on gusty south
winds within an air mass that sent temperatures to 90 degrees across 14
states.
 Readings topped out at 100 degrees in western Minnesota's Granite
Falls, 110 miles west of Minneapolis, and 97 in the Twin Cities. The
extraordinary warmth was the product of compressional warming as winds
converged along a strong frontal system draped across the area. At one
point Tuesday afternoon, temperatures ranged from 42 degrees at Duluth
to 97 at Minneapolis-a 55-degree difference in only 150 miles!

Downpours in Florida

 Flooding downpours continued in Florida where 12.20 inches was reported
at Palm Coast in Flagler County, between St. Augustine and Daytona Beach
on the state's East Coast. The rain isn't over. An additional 8 to 10
inches is to accompany wind-driven squalls for several more days.

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The hot Chicago summers of the 1950s

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Dear Tom,
Growing up in Mendota, Ill. In the 1950s I remember one very hot decade with
only a small fan to cool me off. Just how hot were those summers?

Terry Guilfoyle, Chicago

Dear Terry,
The 1950s brought Chicago and the surrounding Midwest some of its hottest
summers on record. Based on average temperature, five of the city's
11 warmest summers (June, July, August) occurred during that decade,
including 1955, the warmest summer on record with an average temperature of 76.4
degrees. Days in the 90s were rampant with 1955 leading the pack with 46.
Other summers in the 1950s with an excess of 90s were 1953 (42), 1959 (39),
1952 (38) and 1954 (36). Based on Midway Airport data dating back to 1928,
the 1950s logged 276 days of 90 degrees or higher, second only to the "Dust
Bowl" summers of the 1930s with 343 such days.


Warmest air of the year heading our way

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Warm air, responsible for summerlike 90s in the Plains on Tuesday, is
surging toward Chicago. It promises to deliver a three-day string of
80-degree temperatures - the warmest readings here in nearly nine
months.

Rain-organizing jet stream winds have migrated north, to southern
Canada, offering the Chicago region a much needed break from the wet
weather which has produced the area's wettest spring on record at Midway
Airport.

Relief for Florida drought

Sections of Florida in the midst of extreme drought, with some areas
seeing as much as a foot deficit in rain, are being battered by high
winds and heavy rainfall, expected to continue into midweek. Just
southwest of Bunnell, in an area 20 miles northwest of Daytona Beach, a
reported 7.5 inches of rain fell Monday evening, with flooding reported
on secondary roads.
click image to enlarge
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Extreme heat in Chicago--How often?

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Dear Tom,
How often does it get to 100 degrees in Chicago? Has it ever reached 105 degree?

John Behrens Glenview
 
Dear John,
The official Chicago thermometer has cracked the 100-degree mark just 61 times in the city's nearly 139 years of weather records, a frequency of about one every 2.25 years.

It's been nearly four years since the city's last 100-degree day: July 24, 2005 when the high reached 102. Officially the city's hottest reading is 105 degrees and that occurred just once, on July 24, 1934.

Unofficially that temperature has been topped nine times at Midway Airport, mostly during the torrid summers of the 1930s, including a scorching109 on July 23, 1934. During the city's killer heat wave in July 1995, Midway peaked at 106 degrees on July 13, while the official reading at O'Hare International Airport topped out at 104 degrees.
 
A burst of wind--what Mike Zarnek decribes in his e-mail to us as a "mini-twister"---descended on the Des Plaines Canoe Marathon Sunday. Check out Mike's photos. Let me share with  you what he had to say about this in his e-mail account of the event:

"I was at the Des Plaines Canoe Marathon today (5/17/09) taking pictures and as I was standing near a tent a "mini-twister" or micro burst came roaring through right in front of me and tore up the tents.

I happened to have my camera at the ready and fired off a series of shots capturing the series of events.

The canoes in the background started to lift off the ground and people where yelling to "sit in the canoes" to keep them from taking off.

No one was injured."


We're glad to hear that Mike! A fascinating event.  Differential heating helps set these atmospheric swirls into motion. As one surface heats in the sun, the air above it heats and begins ascending.  The in rushing air begins to rotate and sets into motion what you witnessed. Often, such vorticies aren't as strong as the one you witnessed.  But there are many instances when they are and dust devils result.  You had what amounts to a dust devil--without a lot of dust.  No doubt the moist ground from all the recent rain held down the level of dust which Sunday's winds there might otherwise have sent airborne.  THANKS, Mike for a fascinating account of the event and for the terrific pictures!

-Tom Skilling

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Photos courtesy of Mike Zarnek, Mount Prospect, Illinois

Warming starts today in Chicago-peaks midweek

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As the upper-level jet stream flow eases north to the Canadian border, southerly flow returns to the Midwest and western Great Lakes. A cold front will tease Chicago as it slides south over Wisconsin and Lower Michigan Tuesday. The relatively smooth surface of Lake Michigan may allow it to progress further south into Chicago later Tuesday afternoon, but its incursion should be brief. By Wednesday strong southerly flow is expected to change the characteristics of the cold front to that of a warm front, pushing it back north over the same area it passed going south on Tuesday. Highs are expected to warm into the 80s for only the second time this year on Wednesday and probably exceed that mark again Thursday, before a stronger cold front brings much cooler air to the region Friday.
 
Frost warnings over Northeast U.S. early Monday
The coldest portion of the Canadian high pressure air mass shifted east Sunday and National Weather Service Forecast Offices had frost and or freeze warnings in effect for Monday morning over portions of Ohio, Kentucky, West Virginia, Pennsylvania, New York and Vermont.  
 
Good drying weather here this week
Showers and thunderstorms Tuesday and Thursday are expected to be widely scattered, and good drying conditions should occur for the most part, especially south of the metro area.
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Effect of humidity during the winter

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Dear Tom,
A relative who lives in Denver believes that in winter Chicago's higher
outdoor humidity makes one feel colder than in Denver's drier air at the
same outdoor temperature. It's the opposite of humidity's effect in the
summer. Is this correct?

Rob Whitecotton, Hoffman Estates
Dear Rob,
Probably, but the explanation is as much psychological as it is physical.
Winter days with high humidity are often cloudy, gray and gloomy, and that's
the kind of weather that creates an impression of coldness. In the winter,
Chicago experiences many more of those dreary days than does Denver.
Here's a compelling physical explanation: Thermal conductivity -- the rate
at which heat moves from warmer to colder places -- increases as the
relative humidity rises. Even when we're wearing heavy winter clothing, our
bodies lose heat more quickly in humid air than in dry air, and we feel
cold.

Cool Sunday, but big warm-up begins Monday

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With cool Canadian high pressure over the Midwest and Great Lakes, temperatures over northeast Illinois will be hard-pressed to hit 60 degrees today. It's been almost three weeks (high of 55 degrees on April 29) since the mercury last failed to reach at least 60-degrees at Chicago's official O'Hare airport observing site. As the high pressure air mass drifts east, southerly flow will return on Monday, allowing readings to rebound to normal levels. A cold front could sink south through the metro area later Tuesday temporarily shifting winds to the east off Lake Michigan. But indications are it will move back north Wednesday allowing daytime highs to warm into the 80s for just the second time this year. A stronger cooling high pressure system should push the cold front well south of the area later Thursday.
 
A letup in rainfall this week
 
With northeastern Illinois soils saturated due to the wettest spring on record, farmers are still looking for an opportunity to work their fields. While showers are forecast Tuesday and Thursday, the dynamics of the storm-triggering fronts as well as available moisture point to lesser amounts of rainfall and a seven-day period of above-normal drying conditions.

The Arctic Ocean: Ice in retreat

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What is "fetch"?

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Dear Tom,
What the heck is "fetch"?

-Don Schlax, Deerfield

Dear Don,

Like so many words in our language, fetch has a wide variety of meanings. In meteorology,
oceanography, the nautical sciences and related fields, fetch usually refers to the
uninterrupted distance that wind of uniform direction blows across a body of water for the
generation of waves. That's the meaning we use on this weather page.  A north wind (air
moving from north to south) blowing down the full length of Lake Michigan traverses 307
miles of water; it has a wave-generating fetch of 307 miles. A west wind blowing across the
lake's greatest width has a fetch of 118 miles. Air-water temperature difference, wind speed
and fetch are the primary factors that determine wave heights, and an accurate wave forecast
depends upon a correct estimate of all three.

Coolest weekend in 5 weeks gets under way

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Waves of rainfall Friday pushed spring 2009's precipitation tally into
the top spot at Midway Airport. Daytime rains totaled 0.79 inches at the
South Side site, bringing the season's eye-catching total to 15.44
inches-nearly twice the long-term average of 8.04 inches.
Area farmers continue reeling-unable to get spring planting under way.
Many describe the start to the growing season as the worst they've seen.
Heavy as rains were in sections of the Chicago area, central Illinois
recorded local 5-inch-plus totals in thunderstorms Friday.
Computer models suggest drier weather is on the way. While not
completely rain-free, recent forecasts suggest precipitation amounts may
be only half the 2.88 inches that has fallen at Midway in the past two
weeks.
Frost advisories
Frost and freeze advisories were hoisted Friday night across five Upper
Midwest states. In the Chicago area, falling temperatures by Sunday
morning could trigger light frost conditions in the typically coolest
inland locations.

Origin of the term "global warming"

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Dear Tom,
"Global warming" must be a recent phrase because I don't recall hearing it
in the 1970s when I was in college. When did it first get started?

Jeremy Johnson
Dear Jeremy,
Global warming as a distinct phrase has been around for 34 years; it first
appeared in 1975 -- and it has a Chicago connection.
Dr. Wallace Broecker, the world's premier authority on abrupt global climate
change and a long-time researcher at Columbia University in New York, is a
native of Oak Park. We asked Broecker if he originated the term and his
humble response was, "I guess I did, but it was inadvertent."
In 1975, worldwide temperatures had been falling for 20 years (Chicago's
too) and the concern was that a new ice age was imminent. Broecker dismissed
that concern and, in 1975, published a paper titled, "Climate Change: Are We
on the Brink of a Pronounced Global Warming?" The phrase caught on.

Spectacular shots of Wednesday's Missouri tornadoes

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Talk about "up-close" views of an amazing tornado! Check out these photos! Skip Talbot was storm chasing in northern Missouri and has sent along these remarkable photos from several miles east of Kirksville---the northern Missouri community hard hit by a deadly twister Wednesday evening. I want to share with you Skip's description of the storm we're viewing in photos:

"I was out chasing on Wednesday and snagged a few pictures which I thought you might find interesting.

Several miles east of Kirksville, MO, I punched through the storm's core from the north and emerged under the base of a classic supercell.  A wall cloud quickly developed under the rain free base exhibiting rapid rotation.  There was a tightening of the rotation underneath as the rain curtains rapidly swirled around at which point a brief rope tornado developed.  The condensation funnel faded quickly, but the circulation remained on the ground.  The resulting EF-0 had a 9.5 mile path, tracking just north of Edina, MO.  It was just one in a series of tornadoes the storm produced including the deadly Kirksville, MO tornado.  I was able to stay just ahead of the storm, dodging the circulation and hail before I finally had to escape to the south and let it pass.   The tornado had since become rain wrapped, embedded deep in the storm's core behind a dramatic gust front."


These are remarkable shots!  THANKS Skip for sharing them with us!

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Photos courtesy of Skip Talbot

2nd storm outbreak in 3 days to hit region

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The second round of downpour-generating thunderstorms in less than three
days threatens flooding and another outbreak of severe weather Friday
afternoon. Soils are saturated and the 1 to 2 inches or more of rain
expected to fall in sometimes-thundery deluges over the coming 24 hours
has nowhere to go but to run off. Flash flood guidance suggests sections
of Chicago's southern suburbs require less than an inch of rainfall to
initiate flooding.

A northbound warm front will be overrun by humid Gulf air producing
thunderstorms in waves Friday afternoon. As the front swings north and
introduces warm humid air into the Chicago area overnight, a squall line
may form and sweep the area. The Storm Prediction Center indicates a
slight risk of severe weather at that time.

Chilly weekend ahead

The chilliest weekend in five weeks follows Friday night's heavy rains
and thunderstorms. Highs Saturday will struggle to reach 60 degrees, and
Sunday will likely hold in the upper 50s.

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Today's Ask Tom Why

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Dear Tom,
In the "WGN Weather Center Blog" there is a statement that 14 percent of lightning
strikes near Chicago on May 13 were "very dangerous positive strikes." What does that
mean?

Nancy Gilbert, Fairview, NC

Dear Nancy,
The establishment of a nationwide lightning detection network in the early 1990s
enabled researchers to count lightning bolts accurately, and the numbers are stunning:
The United States takes an average of 22 million lightning ground strikes per year. Of
those, 90-95 percent are termed "negative," meaning the flow of electric current is from
the cloud to the ground, and 5-10 percent are "positive," current flowing from ground
to cloud.

All lightning is exceedingly dangerous, of course, but a positive ground strike is even
more so because its electric charge, containing as much as 300,000 amperes and one
billion volts, is up to ten times greater than a negative strike.

Dan Hein shares this photo of the Wilson Skate Park in Uptown. He reports he had to
wade out to clear the drains in order to facilitate draining. Great shot, Dan! THANKS for
sharing it with us!

Tom Skilling


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Photo courtesy of: Dan Hein, Lincoln Park, Chicago

Northern Missouri's Kirksville was dealt a devastating blow when this deadly and incredibly destructive tornado roared through the city late Wednesday. At least one fatality occurred as this twister leveled homes and businesses there. Our friend and frequent contributor to this blog---photographer David Mayhew, who's work is always remarkable----shares these photos of the ominous storm which he took of the storm as it neared Kirkville. David took the first snapshot of this photographic sequence about four miles from the twister while storm chasing Wednesday in northern Missouri. He tells us,

“Got to the honking storm that went through Kirksville MO yesterday. The photos are one of the first funnel to drop taken from about 4 miles away. We then headed to a southern storm that gusted out and later returned to the tornadic storm. NE Missouri is not the most chase friendly area to be in with all the trees and hills, made for extra work! ….more on my website.”

Several sidebars on this storm. At least one early report on this devastating tornado indicated it may have been as much as a quarter to half mile across----a comparatively BIG vortex in the world of twisters.. Also, my colleague Steve Kahn followed the eastward progress of the supercell thunderstorm responsioble for the tornado almost four hours as it traversed a good part of northern Missouri and moved into west-central Illinois. A total of 250 storm reports were relayed from across the nation’s mid-section to NOAA’s Storm Prediction Center Wednesday, 23 of them dealing with the twisters which spun up in the explosively unstable atmosphere which covered the region Wednesday.
Thanks for the always wonderful shots, David! And check out more of David’s work at: www.davidmayhewphotography.com

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Photo courtesy of: David Mayhew, David Mayhew Photography, Chicago, Illinois

Mike Frankowski's photography is always something to behold---and this shot is no
exception! Mike captured lightning accompanying last night’s storms in the Rochelle,
Illinois area. Great shot, Mike---thanks for sharing it with us!

Tom Skilling
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Photo courtesy of Mike Frankowski, South Elgin

After storms, it's sun and lower humidities

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Thunderstorms towering more than 10 miles above Illinois raced across
the state at 50 m.p.h. Wednesday afternoon and evening, unleashing
downpours and producing powerful winds and lightning across an 800-mile
swath of terrain from Wisconsin to the Oklahoma Panhandle. Lightning
data indicated nearly 2,000 cloud-to-ground strokes were occurring
within a 200-mile radius of Chicago late Wednesday-a total exceeding
16,000 strikes was tallied in just six hours' time. The torrential
downpours late Wednesday evening deposited 1.33 inches in just 15
minutes at Milledgeville in western Illinois, northwest of Dixon, and
caused 6 inches of standing water at Morrison near the Quad Cities.
Late-evening storm gusts downed power lines at Mt. Morris southwest of
Rockford as the squall line marched toward the Chicago area, which had
first been placed under a tornado watch around 6 p.m. Wednesday.

Tornadoes in the Heartland
Nearly two dozen reports of tornadoes had been filed with the Storm
Prediction Center across the nation's Heartland as night fell Wednesday.
One especially deadly twister was produced by a rotating thunderstorm
known as a supercell that forecasters tracked across northern Missouri
into west-central Illinois for nearly four hours.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

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1966 tornado in the Arlington Heights area

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Dear Tom,
I remember a tornado that struck the Arlington Heights area many years ago
during the early morning. Do you have any details?

Paul Hirsch
Dear Paul,
The F2 twister struck almost 43 years ago shortly after 6 a.m. on June 9,
1966 as severe thunderstorms packing wind gusts to nearly 80 m.p.h. swept
the Chicago area. The storm first touched down in Hoffman Estates, then
skipped along a 13-mile path through Arlington Heights and Prospect Heights.
One person was killed and 23 injured as the storm produced property damage
totaling nearly $4 million. As bad as the storm was here, it could have been
a lot worse. Just 10 hours earlier, the same thunderstorm complex spawned a
devastating F5 tornado that ravaged Topeka, Kan., killing 16, injuring 450
and causing nearly a quarter billion dollars in property damage along its
21-mile path.

Severe storms threaten area late in the day

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A warm frontal passage and powerful humid winds that take hold Wednesday set the stage
for what could be a significant severe weather outbreak late in the day into Wednesday
night. Clusters of thunderstorms have flared overnight with the northbound front. An ensuing
flood of Gulf air into the area is to produce the most humid daytime humidities since
September. This will provide fuel for a new wave of thunderstorms expected to assemble into
a squall line in eastern Iowa on Wednesday afternoon then surge eastward, most likely
reaching the Chicago area between 7 and 11 p.m. Computer model energy calculations indicate
an atmosphere capable of fostering supercell thunderstorms, which all too often spawn
dangerous wind gusts and tornadoes.
The National Oceanic and Atmospheric Administration's Storm Prediction Center,
responsible for all of the country's tornado and severe thunderstorm watches, placed sections of
Illinois in a moderate risk three days ago. Issuing such a warning three days in advance
is something the agency has done only seven times in the country since 2001.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

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Tornadoes overseas

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Dear Tom,
We always hear about tornadoes in the U.S. but seldom about twisters in
Europe or Africa. Do they occur there?

Deb R., Lincolnwood
Dear Deb,
While three-quarters of the world's tornadoes occur in the United States,
they also develop in most other areas with the exception of the polar
regions. Europe records more than 300 twisters annually, led by England with
an average of 33, while Germany typically records about 10. The majority of
African tornadoes occur in South Africa, but most meteorologists feel that
the number of storms there as well as in many other parts of the world are
greatly underreported. Other countries known for active tornado seasons
include Canada, Australia, Russia, China, Japan and Bangladesh. Bangladesh
has logged at least a dozen tornadoes that killed more than the deadliest
U.S. storm: the 1925 Tri-State Tornado with 695 fatalities.

Shot at the 70s brings a threat of storms

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Monday's sub-par 61-degree high in Chicago came on the heels of the
area's chilliest morning in 18 days. O'Hare International Airport
registered a 39-degree low while some nearby areas registered frost
level temperatures-among them Waukegan (33 degrees), Kenosha (33) and
Northbrook (34). With the chilly air eastbound, frost and freeze
warnings were hoisted overnight across sections of nine states from
Michigan and northern Indiana east to New England.
Tuesday brings with it the prospect of warmer southerly winds expected
to boost Chicago-area temperatures to close to 70 degrees.

Storm-outbreak possible

The warmth is to be joined by an influx of humid Gulf air Tuesday night
and Wednesday-a development that threatens more ominous weather here,
including what may become the area's most extensive outbreak to date. At
least one computer model is developing a major squall line from Michigan
to Texas by early Wednesday evening and thunderstorms which may impact
the Chicago area.

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Today's Ask Tom Why

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Dear Tom,
While visiting Southern Illinois this weekend people were referring to last Friday's storm
as an "inland hurricane." Was it?


Gail Robertson, Christine Steffy, Mary Essling,Daniel Beach, Sean Leidigh


Dear Gail, Christine, Mary, Daniel and Sean,

The storm that ravaged the southern Midwest on May 8th was not a hurricane, but a
derecho, a fast-moving and long-lasting line of thunderstorms producing an almost
continuous path of straight-line wind damage that often extends for more than a 1,000
miles. This massive thunderstorm complex was streaking east at speeds approaching
70 m.p.h. and packing peak winds in excess of 100 m.p.h. After a damage survey, Bill
Davis, head of the National Weather Service in Springfield, Mo., commented that the
storm was like an "inland hurricane" because of its size and its hurricane force winds,
and that terminology spread like wildfire.

Wednesday, Saturday may see 80s, storms

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Chicago's spring has featured a lot of rain but few truly warm days
and very little severe weather. So far the city has logged just one day over
80 degrees -- more than two weeks ago on April 24, when it spiked to a
summery 84 degrees.
While spring rains have been frequent and often heavy, causing
several episodes of flooding, there has been a noticeable lack of severe
weather that typically plagues the region this time of the year. All that
may change this week as surges of warmth on Wednesday and Saturday
may trigger strong thunderstorm development.
Mother's Day featured seasonable temperatures in the Chicago area
with highs reaching the middle and upper 60s. Dry weather was the
rule, though a few showers dampened afternoon festivities. Pea-sized
hail was reported with showers in Oak Lawn and Portage in northwest
Indiana.
Sizzling in the South
Record highs were posted Sunday from Louisiana to Florida. Orlando
reached 97, Ft. Myers 96, Naples 92 and New Orleans 90.
--By Steve Kahn, WGN Weather Center Meteorologist

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The terrible twisters of May 2003

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Dear Tom,
A few years ago I remember that May produced a record number of tornadoes.
Can you provide the details?

David Shaybrook
Dear David,
The month was May 2003, and an extremely volatile atmosphere produced a
record 539 tornadoes responsible for 41 fatalities. Most of the tornadic
activity took place early in the month with nearly 90 percent of the
twisters occurring by May 16. The month featured two horrific outbreak days:
May 4 with 80 twisters that caused 38 deaths, and May 6 with 75 tornadoes
and two deaths. The majority of the severe weather occurred along a frontal
zone that remained anchored from the central and southern Plains east to the
Carolinas. The month's deadliest twister was an F4 storm on May 4 that
struck Denmark in western Tennessee, killing 11. Two deaths were recorded in
far southern Illinois just north of the Ohio River on May 6, one in
Hillerman and the other in Grand Chain.

Mother's Day to be a bit on the cool side

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Mother's Day promises to be a cool one this year with highs struggling to reach the lower
60s. The day will be dry--though a few light showers or sprinkles may develop in the
afternoon--but it should be far better than last year's chilly washout that featured highs
in the 50s and 1 to 2 inches of rain. Though recent Mother's Days have been cool here, the
mercury reached a very warm 88 degrees in 2004 and 85 degrees in 2005. Since the first
proclaimed Mother's Day in 1914, temperatures here have climbed as high as 89 degrees
in 1956 and dropped as low as 29 in 1983. Sunshine returns Monday as temperatures
begin a quick rebound that will boost readings into the lower 80s by Wednesday, courtesy
of increasing southwest winds. The warm-up will be accompanied by a noticeable
increase in moisture, which will lead to the development of clusters of potentially active
thunderstorms that could reach Chicago by Wednesday. Cooler weather will follow in the
storm’s wake Thursday, but another surge of warmth is due to arrive by next weekend.

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Lake Michigan's water level in 1987

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Dear Tom,

In 1987, the top of a large stone offshore from our house was about a foot under water.
Last summer the stone was well out of the water, and now the top of the stone is about
even with the water level. What was the water level in 1987, and how did it compare to
long-term averages and current conditions?

--Richard Ettlinger, Highland Park

Dear Richard,

Data from the National Oceanic and Atmospheric Administration's Great Lakes
Environmental Research Lab confirms your observations. In 1987, Lake Michigan was
about two feet higher than it is today and about a foot higher than the long-term
average. After the recent extended below-normal period, the lake has been steadily
rising. Current levels have increased nearly a foot compared to ayear ago, and with
above-normal precipitation, the rising trend is expected to continue.

Derecho called one of the worst in the past decade

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The deadly squall line that raked far southern Illinois midday Friday,
devastating the Carbondale area on its way across a 1,200-mile swath of
terrain covering sections of nine states, is one for the books. Dr. Joe
Schaefer, director of the National Oceanic and Atmospheric Administration's
Storm Prediction Center, says the "derecho complex is one of
the worst I've seen in the past decade."
Derecho is the term applied to a uniquely long lived and damaging
line of thunderstorms. Their straight line winds and occasional
tornadoes can produce damage over hundreds of miles -- at times, even a
1,000 miles or more. Friday's squall line began as scattered thunderstorms
on the Colorado-Wyoming border, then organized into a line
that was still going strong as it reached eastern Tennessee and the
Carolinas. A second line of storms raced across Illinois late Friday --
this one producing 70 m.p.h. gusts south of the Quad Cities and a brief
tornado touchdown near Little York in western Illinois. The storms
sweep into the Chicago-area overnight, ushering much cooler air into
the region for the Mother's Day weekend.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

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Chicago's coldest and hottest days

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Dear Tom,
Over the 138 years of Chicago weather records, on an average basis what is
the coldest day of the year and what is the hottest day? My guesses are Jan.
24 and July 30 -- but those are just guesses.

Bob Cyborski, Homewood
Dear Bob,
Your guesses are reasonable. Based on Chicago's official temperature records
from 1871 to 2008, the city's coldest day (the day with the lowest average
temperature) is Jan. 28, with an average temperature of 23.1 degrees. Your
guess, Jan. 24, missed by only four days. Chicago's warmest day is July 27,
with 74.8 degrees. You missed that one by three days.
We determined the daily averages for each day of the year by summing the 138
high temperatures and the 138 low temperatures actually observed on each
date, then dividing by 276. Note: Daily normal temperatures are "smoothed
daily averages" for the 30-year period 1971-2000.

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Beautiful Friday morning sunrise

Thanks to Jim Marocchi of Winfield for sharing these pictures of this morning's beautiful sunrise.
The sun, rising amid fog and clouds created these spectacular shots.

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Photos by Jim Marocchi

Steve Kahn WGN Weather Center

Thunderstorms erupted for a second day Thursday. Unlike Wednesday's storms, which
deposited heavy downpours over a majority of the Chicago area, Thursday’s storms
targeted the southern half of the region. Lightning production was far less prolific than
the day before--Thursday's storms produced 20 percent of the cloud-to-ground
strokes observed with Wednesday's storms (1,009 cloud-to-ground strokes versus
5,183). But the faster movement of Thursday's storm generated strong wind gusts
clocked at 58 m.p.h. two miles north of Ottawa just after 4 p.m. A succession of
thunderstorm warnings were issued—one of which extended into southern Cook
County. Other storm gusts included 49 m.p.h. at New Lenox and 46 m.p.h. in
Naperville.

Thursday's temperatures reached 80 degrees at Oswego and New Lenox and in Munster,
Ind.; 79 at Chicago's lakefront; and 77 officially at O’Hare International Airport.

Friday will bring the area its sixth consecutive day with a high of 70 degrees or warmer.


Spring temps rank among warmest 24 percent since 1871

Chicago's temperature since March has averaged 44.9-degrees--1.4-degrees above the
long term 138-year average and 1.2-degrees warmer than the same period a year ago.
It places this spring among the city's warmest 24 percent.

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What is Solar Wind?

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Dear Mr. Skilling,
My older brother who is in high school says the "solar wind" is the wind that blows
when the sun is shining. Is he right?

Jason Landers (3rd grade)

Dear Jason,

Your brother is pulling your leg. The solar wind is not a phenomenon associated with
wind in the Earth's atmosphere; it is a flood of particles (mostly electrons and protons)
that constantly streams off of the sun, in all directions, into space. The particles blast
outward from the sun at incredible but variable speeds -- one million miles per hour is
a good average-- and it is proof that outer space is definitely not a vacuum, as was
once thought.

The solar wind is responsible for one of the most beautiful phenomena of our
atmosphere: northern lights (aurora borealis). Auroras occur when the solar wind's
high-speed particles collide with gases in the Earth's thin upper atmosphere, causing
them to glow.

Kevin Sheely relays these pictures to us of mammatus clouds—the bumpy clouds visible here on the underside of a cumulonimbus (thunderhead cloud) anvil—taken this past Wednesday, May 6. And check out Kevin’s rainbow shots with the same storm. All were taken off I-35 in Osceola, Iowa. GREAT SHOTS, Kevin! Thanks for sharing them with us!

Tom Skilling

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Photos courtesy of Kevin Sheely

Thunderstorms exploded to life Wednesday afternoon as daytime warming destabilized
the atmosphere, encouraging humid air near the surface to ascend and building vast
cumulus clouds that reached 40,000 feet into the atmosphere. Concentrated downpours
from the towering thunderheads drenched Wrigleyville with 1.48 inches of rain and
produced brief flooding in spots. Midway Airport's 0.84 inches of rain through late
evening pushed the city's spring rainfall tally to 13.41 inches-re-establishing the
season to date as the wettest on record here.

Lots of lightning

The first flashes of lightning with Wednesday's fast developing storms occurred
around 1 p.m. on the Mississippi River between Iowa and Wisconsin. Storm development
was so rapid, lightning was arching across Chicago skies only three hours later. A total
of 5,183 cloud-to-ground strokes had been recorded over the six-hour period through
8 p.m. within a 200-miles radius of Chicago. 38% of them especially high amperage
"positive lightning". Typically only 10 percent of lightning bears a positive charge.

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Snow on Mother's Day?

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Dear Tom,
My mother says that she remembers a Mother's day when it actually snowed in
Chicago? Is she right?

Kimberly Raven

Dear Kimberly,
While we'd like every Mother's Day to be sunny and warm, the weather doesn't always
cooperate. Your mother is indeed right if she is remembering Mother's Day May 9,
1954 , a chilly rainy day that officially registered a trace of snow at the Midway Airport
site during the early morning hours. The morning low at Midway fell to 36 degrees, but
many inland suburban areas were even colder, dropping to near freezing. The afternoon
was only slightly better with highs rebounding just into the lower and middle 50s. The
extreme variability of Chicago's spring weather was highlighted two years later on
Mother's day 1956 when the city basked in summery 89 degree heat, making May 13,
1956 Chicago's warmest Mother's day on record.

With soils in many locations still wet, our northern Illinois farmers have been seriously
hampered in trying to plant this year’s corn crop. Still, our friend John Hazzard, who
farms in the Wilmington area of Will County and always provides us timely updates on
planting and crop progress during the growing season, sends us these pictures of some
limited corn planting which has gotten underway in his area. John tells us:


“The farmers in this picture are David and John Meyer's they farm 1100 acres between
Wilmington and Kankakee Ill. Not all fields are dry enough as more drying will be
needed to keep the planters rolling. This field has a sandy type soil which enabled Dave
and John to get a start.They’re hoping the string of dry day's continue for a couple of
weeks so they can get everything planted by then.”

THANKS for the update, John!

Tom Skilling

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Photos courtesy of John Hazzard, Wilmington, Illinois

Rains to return with thunder after 4 day hiatus

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Rain-weary Chicago-area residents have just witnessed the longest spell
of precipitation-free weather in nearly a month. But thunderstorm
prospects are to surge later Wednesday afternoon and evening, and again
Thursday afternoon and evening, with an influx of Gulf moisture. A
spotty shower or two isn't out of the realm of possibility into early
Wednesday afternoon. But the primary thunderstorm development is to be
stoked by daytime heating that is to take place beneath a pool of
comparatively cool air aloft. Heating of the lower atmosphere encourages
air to become buoyant and ascend into cooler reaches of the atmosphere.
Computer model vertical-temperature profiles suggest this process could
produce towering cumulonimbus clouds-the suffix "nimbus" always refers
to precipitation falling from clouds-which could extend to heights of
nearly 40,000 feet. Modest winds at the higher steering levels of the
atmosphere could allow any thunderstorms that form to move comparatively
slowly, producing locally heavy rain totals.

70-degree spell to extend to 6 days

The current mild spell that began Sunday is likely to continue through
Friday. If forecasts verify, the six-day string would arrive nearly two
weeks earlier than the average starting date of the season's first
six-day 70-degree spell, (May 15).

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Lake Michigan water levels after heavy rainfall

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Dear Tom,
Recently you've stated that we've had one of the wettest springs in 80
years. Is all this extra rainfall having any positive effect on the water
level in Lake Michigan, which has been very low over the past several years?

Chuck Kukla, Chicago

Dear Chuck,
Water levels in the Lake Michigan-Lake Huron system (hydrologically, they
are one lake) have indeed responded favorably to above-normal precipitation
across the lakes' drainage basin. The lakes' water level now stands 11
inches above the year-ago reading, but it is still about eight inches below
its long-term average level.

Overall precipitation here at Chicago has been far above normal for 15
months. But precipitation which falls over Chicago has little impact on Lake
Michigan because most water from northeast Illinois drains to the
Mississippi River. But Chicago's wet weather has been part of a much broader
soggy pattern which has affected much of the lakes' drainage basin.

Sagging jet stream has kept big rains south

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The Chicago area is in the midst of its most extended break in rainfall of the past three
weeks. More than half of the days since April's open—19 of the past 35 days (54
percent of them)--have registered rain. The past two weeks alone have seen more than
3 inches of rain (3.16 inches) fall. A shift in the jet stream is behind the drop in rainfall.
Pockets of especially strong winds within jet streams--referred to by meteorologists as
jet streaks--act to lift and cool air, igniting thunderstorm development. But the jet
stream itself has sagged south in recent days, which has diverted the most organized
thunderstorms well south of Chicago.

With rainfall and accompanying cloud cover more scarce than in many recent days,
temperatures have been able to surge. Monday’s 70 degree high followed a similar high
on Sunday and marked the ninth time in 2009 the mercury has reached or exceeded the
70-degree mark. Additional 70s are predicted each day through Friday. And it's not out
of the question this year's second 80-degree day may occur Thursday if widespread
thunderstorms hold off until after sunset.

Thunderstorms will flare Wednesday, however, and could tap a northbound flood of Gulf
moisture to produce downpours at some locations.

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Cooler nights when air is dry

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Dear Tom,
Nights are cooler when there is less humidity in the air. Why is this?

Thomas Crawford

Dear Thomas,
It's a phenomenon familiar to weather forecasters: Temperatures rise and fall much
faster when the air is dry than when it is moist. Not only are nights cooler on dry days
(as you have stated), the days are also warmer. When air is warmed (or cooled), the
temperature of all its component gases must warm (or cool) as well. However, it takes
more heat (provided by sunlight) to warm water vapor than it does the mix of gases that
comprise air devoid of water vapor. Result: Daytime temperatures rise more quickly in
dry than in moist air. At night, it's the reverse. Moist air contains more heat energy than
dry air at the same temperature, and so it must lose more heat in order to cool. As a
consequence, moist air cools more slowly than dry air.

Kites above Montrose Hill on Chicago's lakefront

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Check out ALL the airborne kites above Montrose Hill on Chicago's lakefront Saturday---perfect kite-flying weather!

Thanks to Colden Searles for sharing these shots of the Montrose Hill Kite Festival held Saturday, May 2. Colton tells us the photos were taken around 2:30 p.m. in the midst of perfect kite-flying weather!!

THANKS Colton!!

Tom Skilling

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Photo courtesy of Colden M. Searles, Chicago

A couple of dry days before rain revisits city

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High pressure anchored over the Great Lakes will remain strong
across northern Illinois on Monday and then weaken Tuesday as it
heads east and gives way to an approaching low-pressure system
from the west. Soils should continue to dry, and rivers and streams
slowly fall. But clouds and as much as a half-inch to an inch of rain
should spread over the Chicago area Wednesday. After a brief respite
and warm-up Thursday, another weather system should bring
quarter- to half-inch rains Friday.
Storms again hit Southeast
Sunday afternoon, a north-south line of thunderstorms tracked east
through the Gulf Coast states with reports of tornadoes, large hail and
widespread wind damage. There were many reports of trees and
power lines down. A woman was killed by a falling tree in Jones
County, Miss., and a report out of Perry County in west-central Alabama
indicated thousands of trees downed. As the storms continued
east, a severe thunderstorm watch was in effect Sunday evening for
western South Carolina.
--By Paul Dailey, WGN Weather Center Meteorologist

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Weather witticisms

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Dear Tom,
Every now and then you print interesting comments from knowledgeable weather
people. Which comments are your favorites?

Steven Seligsohn
Dear Steven,
Here are four, in no particular order: "Remember, you'll never see, hear nor
feel the lightning strike which kills you."
(Roger Edwards, a meteorologist
with the Storm Prediction Center in Norman, Okla.) "A dry season, a strong
wind, and an accidental fire, whenever they occur together, will do the
work."
(Increase A. Lapham of the Chicago Weather Bureau, commenting about
the Chicago Fire of Oct. 8-10, 1871.)
And here are two gems from non-weather people: "What's good about March?
Well, for one thing, it keeps February and April apart."
(Walt Kelly,
creator of the comic strip "Pogo".) Finally, "Climate is what we expect,
weather is what we get."
(Novelist Robert A. Heinlein.)

Break in rains allow rivers to fall and fields to dry

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Northeast Illinois is catching a welcome--albeit short-- break in this
spring's prolonged wet pattern. Area rivers and streams are running close to
bankfull or overflowing and soils everywhere are soaked. Indications are the
next storm system will spread showers and thunderstorms back into this area
Tuesday night and Wednesday. That would mean a five-day respite that might
allow rivers and streams to absorb the next round of rainfall without
significant flooding, and some farmers in better-drained areas a chance to
briefly get back into the fields.

Severe storms hit the southeastern U.S.

Saturday afternoon and evening tornado watches were issued covering portions
of states from Texas to Alabama where in addition to many tornado
warnings, there were many reports of golfball-sized hail and damaging winds.
Around 3:30 p.m., the roof of the Dallas Cowboy training facilities
collapsed with several injuries reported.

More rain in the weeks ahead

In the next couple weeks, northern Illinois and southern Wisconsin seem to
be targeted for frequent rain-producing low pressure systems. The National
Weather Service extended 8 to 14-day outlook for May 10-16 forecasts above
normal rainfall over the Midwest and Great Lakes.

Wet? You bet!

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Chicago's lowest humidity vs. lowest in U.S.

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Dear Tom,
What is the lowest humidity ever recorded in Chicago, and how does that compare to
the lowest humidity readings elsewhere in the U.S.?

--David Hardt

Dear David,

Chicago weather historian Frank Wachowski tells us that Chicago’s lowest relative
humidity value is 13 percent, recorded on three occasions: May 10, 1934, (the
temperature was 72 degrees and the dew point 18 degrees); April 11, 1956, (53 degrees,
dew point 4); and April 8, 1971, (77 degrees, dew point 22). In Chicago, low humidity
episodes are most common on warm, windy days in early spring or late fall. Nationally,
the lowest humidity values invariably occur in desert areas. A few cities in the
Southwest have recorded relative humidity values of 2 percent, including Las Vegas,
Phoenix and Yuma, Ariz.

Weekend is first in 3 weeks to be free of rains

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The first full weekend of May is to be the nicest here in three weeks. Heavy
rains, including thundery downpours which produced flooding and hail this
past Saturday and Sunday, were among those which rendered the past two
weekends wash-outs. Rainfall at O'Hare totaled 1.41" last weekend and 0.90"
the weekend before. It appears the only threat of rain this weekend comes in
the form of passing sprinkles or even a few brief light showers Sunday
afternoon -- precipitation which may bypass some sections of the Chicago area.
The break in rainfall comes on the heels of an April deemed Friday 6th
wettest in 114 years of records by state climatologist Dr. Jim Angel of the
Midwestern Regional Climate Center. Angel reports statewide precipitation
averaged 6.20" versus the 3.80" considered normal.
Area farmers like Dave Behrens, who farms near Woodstock in McHenry County,
stymied in their attempt to get corn and soybeans in the ground, have grown
frustrated by the recent abnormally wet pattern. Behrens has planted just 5
percent of his corn versus 80 percent a year ago and says, "This is the
worst start in my 23 years of farming."
Weather improvement temporary; waves of rainfall
to keep coming the next two weeks

The weather improvement here is temporary -- likely to last into Tuesday.
That's providing a wet early week storm passes south of the city as
currently anticipated. A southward jog in the jet stream is behind the
improved picture -- though the thunderstorm spawning, high-altitude river of
air is to drift back north into the Midwest by midweek igniting clusters of
thunderstorms -- initially scattered Tuesday night then increasing in coverage
Wednesday. Widespread 1-2" rainfalls are possible.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

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Contrails

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Dear Tom,
I have noticed that on some days almost every airplane in the sky has a
white plume coming from it. At other times there is no plume. Is this a
function of atmospheric conditions, the planes, or both?

Sheri Baker, Sycamore
Dear Sheri,
Both. Those cloudlike streamers behind aircraft are known as contrails. Two
distinct processes contribute to their formation.
Among the very hot gases in the combustion exhaust of jet aircraft is a
great deal of water vapor. As the swept path of the aircraft cools, that
water vapor usually condenses into ice particles that we see as contrails.
However, very dry air can inhibit their formation.
Second, air pressure reduction accompanying the motion of air over aircraft
wingtips can chill the air sufficiently to cause condensation. In humid air,
contrails can persist for hours and encourage the formation of a layer of
cirrus clouds.

Oklahoma Supercell Thursday evening

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Our friend and photographer David Mayhew sends us these shots of a
high-precipitation-producing (or "HP") supercell taken last night in
Oklahoma.
Fantastic shots, David -- THANKS for sharing them with us!
--Tom Skilling, WGN-TV Weather Center

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Photos courtesy of David Mayhew, David Mayhew Photography-Chicago