June 2007 Archives

The spell of pleasantly cool temperatures and low humidities that has dominated the Chicago weather scene in recent days is drawing to a close. Readings more typical of the season return to the area Monday and Tuesday as northeast winds, prevalent since Thursday, give way to gusty southwest breezes by Tuesday.
The big weather story continues to be a stalled storm system that has been delivering persistent, massive, flooding rains to portions of Texas, Oklahoma, Kansas and southern Missouri. Five-day rain totals at many locations in those states exceed 15 inches, and this deluge is on top of record or near-record wet conditions in May and the first three weeks of June. Forecasts unfortunately offer the prospect of additional heavy rain there today through Tuesday, after which the area should dry out.
-By Richard Koeneman, WGN Weather Center Meteorologist

After two days of afternoon temperatures running about 10 degrees below the city’s late-June normal high in the lower 80s, area readings bounce back to about 80º this weekend.
The warm-up gains strength early in the work week, culminating with afternoon temperatures cracking 90º on Tuesday and Wednesday. Humidity, too, will be climbing to uncomfortable levels coincident with the arrival of the 90° heat.
Chicago’s year-to-date rainfall, 14.57”, is a little below normal (16.48”)—but a pittance when compared to the deluges of rain that have swamped Oklahoma and Texas and portions of surrounding states in recent weeks. Stillwater, Okla., west of Tulsa, has logged 23.06” just in May and June, and Gainesville, Texas, north of Dallas, 22.43” in the same period. Computer forecasts promise no relief for those waterlogged areas. An upper-level storm system stalled there, remains in place through the weekend.
--By Richard Koeneman, WGN Weather Center Meteorologist

Thanks to Lynnie Deroche from Darien and James Kloc from Pingree Grove for capturing and sharing these photos of last night's beautiful sunset.

Photo by Lynnie Deroche

Photo by James Kloc

It’s not often that Chicago’s afternoon temperatures fail to rise above the lower 70s during the closing days of June. Cool-weather lovers are relishing today’s chilly interlude that is delivering afternoon readings more typical of early October than late June. In fact, readings as cool as yesterday’s 74º and this afternoon’s 73º occur only about one day in 12 at the end of June. Summer, however, is not to be put off. A multi-day warming trend—beginning tomorrow—will carry the city’s temperatures back into the lower 90s by this coming Tuesday. Humidity will also reach uncomfortable levels. The National Weather Service advises that northerly winds blowing down the full length of Lake Michigan have generated conditions favorable for rip currents on the Indiana shores of the lake.
--By Richard Koeneman, WGN Weather Center Meteorologist

Chicago weather historian Frank Wachowski informs us that June has been warm, with an average temperature, as of the 27th, of 73.4º. That ranks 12th warmest in 80 years (1928-2007) of temperature records at Midway Airport.
We identified 16 years with comparable average temperatures through the 27th, then tallied the 90° occurrences in those years. Those 16 years produced an average of 32 days per year at or above 90º, versus the long-term average of 24 days—a strong suggestion that the above-normal trend of temperatures thus far this summer is likely to persist in July and August. In contrast, pleasantly cool and refreshingly dry air is forecast to dominate area weather through the next few days, but computer models suggest a turn to higher temps and increasing humidity by early next week.
-By Tom Skilling, WGN-TV Chief Meteorologist

Rain fell between 2 and 4 p.m. on Chicago’s north side as heavily as in some hurricanes and tropical storms, coming down at one point at nearly 4” an hour. (That’s a pace which equals the rate at which rain fell in deadly Tropical Storm Allison which submerged sections of Houston, Texas under nearly 37” of rain in June, 2001.)
At the height of Tuesday afternoon’s storms, cloud-to -ground lightning flashed more than 1,700 times in single 10- minute period within a 225-mile radius of Chicago. Lightning accompanied the blinding downpours here which forced traffic to a standstill on the North Side, swamping sections of the city’s Lakeview neighborhood with 3.70” of rain while drenching the area adjacent to Wrigley Field with 3.46”. Sections of north Lakeshore Drive were closed to traffic for a time into the evening and a number of north side roads were seriously flooded.
--By Tom Skilling, WGN-TV Chief Meteorologist

Temperatures have plunged more than 20-degrees—falling more than 20-degrees from 92-degree to 71-degrees (as of 3:36 pm Tuesday) at CLTV’s OakBrook studios. WeatherBug temperature sensors indicate a 21-degree drop at Darien, 19-degrees at Hinsdale and 17-degrees at LeMont, Westchester, Glenview and Niles. Large temperature drops are common with thunderstorms. The tops of today’s 50,000 ft. tall t-storms have temperatures near -86-degrees F!

Also, rainfall of 2.07” has been reported by National Weather Service observers near Ottawa in LaSalle County. The rain there fell between 2:30 and 3:30 pm.

Tom Skilling

Tuesday’s moisture-laden atmosphere is producing clusters of strong thunderstorms which cover just 30% of the greater metro area but are hitting affected areas hard. Cook, Grundy, Kendall and Will counties have been placed under urban flood advisories because of local 2”+ rains. Rainfall has been localized but torrential under the heaviest storms Tuesday afternoon. Radar scans have indicated cloud tops up to 50,000 ft.—little surprise given the fact weather balloon soundings measured more than 1.50” is evaporated in the 70-degree dewpoint environment. This plus 90-degree temperatures prior to the onset of thunderstorms have destabilized the atmosphere and allowed thunderstorms to bubble into existence. These storms are selective—drenching one area and ignoring others. With so much available moisture, it’s little wonder our WeatherBug rain sensors indicate 1.65” has fallen at Lane Tech High School, 1.80” at southwest suburban Morris, 1.20” in Wheaton and over 1” at Wrigley Field. One National Weather Service observer reported 2.12” had fallen near Coal City in Grundy County between 2 and 2:30 pm and another thunderstorm produced 0.75” in 15 minutes at Arlington Heights. One noteworthy concern beside the periods of blinding rain and a few reports of brief wind gusts to 60 mph is the quantity of cloud to ground lightning being produced by some of these storms. Lightning data indicates as many as 1,773 cloud to ground strokes have occurred in a recent 10 minute period Tuesday afternoon. An unusually high percentage of these have been “positive” strokes, indicating the lightning discharges are lowering positive charge to earth. Studies have shown positive lightning strokes can be more energetic than the negatively charged counterparts. These often higher amperage discharges are often the most dangerous strokes, capable of setting fires and causing injury. Storm clusters are likely to affect sections of the Chicago metro area into evening then fade slowly as temperatures drop beyond sunset. New storm development is likely Wednesday afternoon and evening.

Tom Skilling
Chief Meteorologist
WGN-TV

June, already the 7th warmest at O’Hare since weather observations began there in 1959, promises to get even warmer Tuesday. Better organized, muggier south winds override the cooling lake breezes which have moderated temperatures in Chicago over the past six days. Tuesday’s predicted 93° high would equal 2007’s hottest reading to date (set back on June 16) and become the city’s sixth official 90° temperature to date. And with gusty SSW winds taking hold, 90s are likely to make it into the Loop and across area beaches where 70s have been common in recent days.
Monday’s high at O’Hare fell just one-degree shy of 90° but marked the 31st time the mercury here has reached or exceeded 80°. The tally far exceeds last year’s 19 highs of 80°+ and marks the most 80s here this early in 16 years.
-By Tom Skilling, WGN-TV Chief Meteorologist

Sluggish low pressure meandering across the southern Midwest played an instrumental role in bringing cloudy and cool weather to the Chicago area this weekend. Persistent cloudiness made sunshine a no-show Saturday, and after a dreary morning, the city managed to eke out less than 20 percent of possible sunshine on Sunday thanks to some breaks in the clouds during the afternoon.
Another batch of low cloudiness and even some fog in outlying areas should blanket the area Monday morning, but a generous dose of afternoon sun should allow temperatures to climb into the 80s, along with increasing humidity. Highs could even hit 90º Tuesday, though more clouds and possible thunderstorms could keep many area readings in the 80s.
After peppering the Chicago area with rain the past few days, showers stayed south of the area Sunday. Several weak “cold-air” type funnels were sighted in central Illinois, but none touched down.
--By Steve Kahn, WGN Weather Center Meteorologist

It really was the second full day of summer 2007, but Saturday seemed more like fall here as clouds, gusty east winds and light showers combined to produce an autumnal-like of high of 67º, a value typical of Oct. 4. It was the coolest June 23 here since 1979 when the high was only 58°. Quite unusual for June, the day was also totally sunless, and was the city’s first zero percent sunshine day since May 26. Areas north of the city received only nuisance light showers totaling just a few hundredths of an inch, while south and west sections measured substantially more, including 0.44” at Midway, 0.67” at Aurora, 0.96” at Romeoville, and 1.80” at Sandwich.
Temperatures should rebound quickly beginning Sunday as winds shift into the south. Air conditioners should be humming by Monday as highs jump into the 90s and combine with increasingly uncomfortable humidity levels.
--By Steve Kahn, WGN Weather Center Meteorologist

Roads and highways—even entire communities—were reportedly submerged by flood waters late Friday across sections of eastern Iowa and west-central Illinois in the wake of at least three waves of torrential downpours which began Thursday night. Ground reports in a corridor extending from near Des Moines to Cedar Rapids and the Quad Cities south to Quincy, Ill., put rainfall totals at up to 7-8”. Doppler radar estimates ranged as high as 10” just west of Cedar Rapids.
Rescues were taking place Friday evening to free stranded motorists from vehicles trapped in flood waters. The flooding in sections of eastern Iowa was being described as the worst since 1993. In that benchmark meteorological event, Iowa was dubbed the “Sixth Great Lake” because of all the standing water there.
Thundery rains are to erupt again in waves Saturday, targeting areas in Illinois primarily south and west of Chicago.
--By Tom Skilling, WGN-TV Chief Meteorologist

Thunderstorms, deflected away from Chicago much of Thursday by cool east winds, finally reached sections of the region in the late evening—but in a diminishing stage. Areas south and west sections were predicted to bear the brunt of the most active overnight storms. Friday opens with the last of those storms south of the city.
Thursday morning’s cold frontal passage sent temps tumbling 14° from morning highs. O’Hare’s 77° was the coolest in 15 days. Dew points—a measure of atmospheric moisture—plunged to the upper 30s in sections of the metro area signaling the presence of remarkably dry air. It’s another reason heavy t-storms which pounded an area from South Dakota to Wisconsin had little success reaching Chicago at full strength. By late Thursday, 275 reports of severe weather had been logged including golf ball size hail in Gann Valley, S.D. which destroyed 90% of the grain crop.
--By Tom Skilling, WGN-TV Chief Meteorologist

Michael Durr of Westmont, Illinois has sent us these marvelous time exposure photographs taken from his backyard in Westmont of the International Space Shuttle and the Space Shuttle Atlantis passing over the Chicago area. He took these photos at 9:52 pm Wednesday evening, June 20, 2007 and e-mailed us that "it's amazing to think about people flying over us at that height and speed."

How true! Many thanks for sharing these with us Michael! They are spectacular!

-Tom Skilling


Photo Courtesy: Michael Durr

Severe thunderstorms require warm, humid air to rise and cool in order to develop. That's happening to Chicago's west in Iowa and southern Minnesota and there are severe thunderstorm watches and vigorous thunderstorms under development effect there. But because of the cool, less humid northeast wind blowing across the Chicago metro area in the wake of a mid-morning cold frontal passage, the atmosphere has stabilized---i.e. air is not cooling with height at a pace required to encourage air to rise. With cool east winds expected to be a fixture here the remainder of this afternoon and into tonight, the threat of severe weather is being deflected to the west and south of the city.

Powerful storms ARE likely to flare west and south of the city later Thursday night into Friday, and there, severe weather watches or warnings may become necessary overnight. It's possible some thundery weather may manage to reach the city late Thursday night, but Chicago and areas north are not at risk for severe weather in the short term. Looking several days out appears a much different story. Strong possibly severe thunderstorms threaten to reach Chicago later Friday night into Saturday when a strong east/southeastbound disturbance is to traverse Illinois.

Until then, the severe threat is greatest in areas west and south of Chicago. Thunderstorms in these areas will be capable of torrential downpours which may deposit some flood-provoking rainfalls.

Tom Skilling
Chief Meteorologist, WGN-TV Weather

Severe thunderstorms erupted along a cold front stretched out across the upper Midwest Wednesday afternoon pelting the region with hail, high winds and heavy rainfall. Softball size hail crashed to Earth at Harris Minn., about 50 miles north of the Twin Cities, while hail ranging in size from golf ball to tea cup covered the ground in areas around Marquette in Michigan’s upper peninsula. A twister touched down at Antigo, Wisc., northeast of Wausau, downing trees and unroofing a shed.
This storm system will be impacting the Chicago area beginning tonight as a precursor to a blast of heat and humidity that will send temperatures soaring back into the 90s by Sunday for a potential four day stint. With four 90º days already on the books here this June, the city could log as many as eight by next Wednesday, the most for a June 1-27 here since nine were recorded a dozen years ago in 1995.
-By Steve Kahn, WGN Weather Center Meteorologist

Dan and Marcia Smith, formerly from West Chicago, Illinois and currently residing in Rogers, Minnesota (just northwest of the Twin Cities) sent us this spectacular shot of a thunderstorm that passed through their area about an hour earlier this evening.

Photo Credit: Dan Smith, Rogers, Minn.

Area residents were treated to a brief but spectacular glimpse of the International Space Station and the Shuttle Atlantis late Tuesday evening. Skies were cloudless and visibilities unlimited as the two spacecraft moved from the western sky to the eastern horizon between 9:31 and 9:35 p.m. before disappearing in the Earth’s shadow. If weather permits, area residents may get another chance to view the Space Station Wednesday evening beginning around 9:53 p.m., says Triton College astronomer Dan Joyce. The only fly in the ointment would be the arrival of thin high clouds blowing off distant storms. Joyce advises looking for a small moving object in the western sky just south of Venus—the brightest object visible in the early evening sky this time of the year. The Space Station may only be about a third as bright as Venus and will be seen moving south/southeastward. It’s likely to be highest in the sky around 9:55 p.m. and will disappear a minute or so later.
--By Tom Skilling, WGN-TV Chief Meteorologist

Monday evening's setting sun, a hazy, humid environment and distant towering cumulus clouds combined to produce this amazing scene photographed and relayed to us by Larry Jahn of downstate Macomb, Ill. The rays visible here are referred to as crepuscular rays.
That there are gaps in these rays indicates light from Monday evening's setting sun was being blocked by distant cloud towers -- the kind which might well include tall cumulonimbus clouds (thunderheads). Our sincere thanks to Larry Jahn for sharing these spectacular shots with us!
--By Tom Skilling, WGN-TV Chief Meteorologist

Tom Jensen shares these shots of a towering cumulonimbus cloud (thunderhead) similar to those which produced severe weather Monday afternoon and evening. He photographed this cloud around 6:30 p.m. Monday evening. A canopy of high ice clouds (cirrostratus) associated with the thunderstorm's anvil is clearly visible at the top of each photo.
Doppler radar scans of Monday's cloud tops show many of the day's thunderstorms reached heights of 48,000 feet -- one even topped out at 54,000 feet. It's interesting to note air pressures at that altitude are around 150 mb. -- roughly 15 percent the density of air at sea level. Just as extraordinary is the fact air temperatures at cloud top-level Monday were near -86 degrees!
Thanks Tom for these beautiful shots!!
--By Tom Skilling, WGN-TV Chief Meteorologist

Photos courtesy: Tom Jensen, Tinley Park

Hot weather doesn’t relinquish its grip on an area’s weather easily and Monday was no exception. The day’s alternately stormy afternoon and evening weather unleashed 60+ m.p.h. wind gusts and 1” hail, resulting in property damage near Merrillville, Dyer, Crown Point, Griffith and St. John, Ind.; and farther west in Grundy County’s Morris, Ill. The gusts with several mid-afternoon storms in northwest Indiana bent utility poles. They remained standing—but at a 45-degree angle to the ground near Merrillville.
Heavy damage was reported in central Morris from Old Stage Road to east Washington Street in what may have been a microburst. The collapse of 47,000-foot-top thunderstorms allowed dense rain-cooled air suspended aloft by the storms’ updrafts to come crashing to earth, where it fanned out as the water from a running hose might if pointed at the ground. New storms northwest of Chicago late Monday evening made barricades necessary in Rockton, Ill., southwest of Beloit. Water stood three feet deep there, and roads were submerged.
Flood warnings were issued for Winnebago, Boone and McHenry counties in Illinois and Rock County, Wis. The eastbound thunderstorms threatened to bring heavy rains to other sections of the Chicago area overnight.
--By Tom Skilling, WGN-TV Chief Meteorologist

With Monday’s high expected to top the 90º mark again, the city will have experienced a mini four-day heat wave more than six weeks earlier than last year. Four consecutive 90s did not occur in 2006 until the July 28-31 period, a string that eventually reached six days when it finally ended on Aug. 2.
The city’s official 91º high made Father’s Day 2007 the hottest here in a dozen years since the 93º reading on June 18, 1995. A few thunderstorms erupted during the hot and humid afternoon, which were actually triggered by the inland-moving lake breeze front. Rainfall was spotty and light with most areas that received rain getting less than one-tenth of an inch.
A cold front approaching the city Monday night should trigger a round of strong thunderstorms that promise much-needed rain, but also raise the specter of severe weather.
Cool weather will follow for midweek, but more heat should return next weekend.
--By Steve Kahn, WGN Weather Center Meteorologist

It didn’t rain everywhere, but the widely scattered thunderstorms that developed on a hot and humid Saturday afternoon brought welcome rainfall to parts of Chicago and northwest Indiana. Nearly an inch (0.94”) fell at Highland, Ind. and 0.52” dampened Lincoln park at the Peggy Notebaert Museum. Rainfall has been a scarce commodity here this month, despite measurable rain on each of the first six days. Since then the area has been rain-free except for some heavy thunderstorms near Wisconsin early on June 8. The 10 day string of sunny, warm days has steadily dried out area soils with plants starting to show signs of stress from lack of moisture.
More storms should erupt in similar low-coverage fashion Sunday afternoon and evening, but a more significant rain event, in terms of amounts and areal coverage, should target this area Monday night as a robust cold front passes through the region.
--By Steve Kahn, WGN Weather Center Meteorologist

Friday’s 91° high tied the year’s warmest reading and marked only the third time in the past 38 years a June 15 has been as warm or warmer. With 90s predicted over the next three days, this weekend is to be Chicago’s warmest since late July. What’s more, the string of four 90s arrives more than a month earlier than a year ago.
Lake Michigan reached its warmest temperature of the year Friday. While Chicago’s shoreline reading jumped to 72° near the James Jardine Water Purification Plant next to Navy Pier, the satellite-sensed average water temperature across the lake’s entire 22,300-square-mile surface surged to 64.9°, a reading nearly 30 degrees above the lake’s 35° low point on March 22.
Warming lake waters have rendered lake breezes far weaker than a few months ago. Lake breezes Friday only lowered shoreline highs to the mid 80s—well above the mid-40° air temperatures which occurred with northeast winds back in April.
--By Tom Skilling, WGN-TV Chief Meteorologist

Lake Michigan’s shoreline water temperature broke above 70° for the first time in 2007 Thursday. But it was the area’s hot inland temperatures which made news. Readings from Plainfield to Geneva, DeKalb and Algonquin soared into the mid 90s making it the hottest day of the year at many inland locations.
Warming lake waters this time of year limit the degree and scope of the cooling which sweeps ashore when winds blow from the east. Rather than sending readings into free fall, as might have happened a month or two ago, winds off the lake act to more modestly air condition areas closest to Lake Michigan’s waters. As a result, Northerly Island’s temperature topped out at 77° Friday while temperatures hit 96° at the WeatherBug temp sensor in southwest suburban Plainfield.
-By Tom Skilling, WGN-TV Chief Meteorologist

For the past three days (beginning this past Monday), there hasn’t been a cloud in the sky above Chicago. The city has received 100% of its possible sunshine. That’s not a common occurrence. The last time three back-to-back 100% sunny days occurred here was April 12, 13 and 14, 2005. While spectacular weather is predicted again Thursday, the arrival of some high and mid-level clouds from the northeast this afternoon is likely to deny us a fourth day completely free of clouds. (Note: Should Thursday’s clouds fail to materialize, Chicago’s streak of 100% cloud-free days would extend to four days— the most here in two decades of Junes).
The month’s temperatures have responded to all the sun. June’s opening 13 days have averaged 68.9°—warm enough to rank 34th warmest since 1871. But high evaporation rates are drying area soils which will make any rainfall which arrives next Monday welcome.
--By Tom Skilling, WGN-TV Chief Meteorologist

Wednesday’s unlimited sunshine boosts to seven the number of consecutive rain-free days over much of the Chicago metro area, excluding sections of Lake, McHenry, Boone, Winnebago and northern Kane counties walloped by last Thursday night’s cloudburst. Though subsoil moisture still has much of the region’s vegetation looking healthy and green, the period since May 1 has seen only 2.86”—far below the 137-year long-term average of 5.20”. That makes the period the 22nd driest on the books here since 1871. With June’s soil moisture loss to the atmosphere at the hands of evaporation in excess of 6”, any gap in rainfall results in rapid drying.
The build-up of ozone in recent days is behind the Air Pollution Action Day declared Wednesday. Ozone, which forms as a by-product when certain atmospheric pollutants are encouraged by sunlight to react, tends to peak in the afternoon and early evening hours.
-By Tom Skilling, WGN-TV Chief Meteorologist

A year ago, Chicago was in the midst of an unseasonably cool four-day late-season stretch of daytime 60s. This year couldn’t be more different. For the 22nd time this year (versus last year’s 13), Chicago’s official temperature is to top out well above 80° Tuesday on a second consecutive day with 100% of its possible sunshine. That means 2007 is maintaining a pace of 80°+ high temperature production 62% ahead of a year ago. It’s a trend which has historically segued into summers which have averaged 31 days at or above 90° instead of the 21 considered normal.
June 2007’s 68.1° temp is running more than 2° above the long term (137 year) average and 3.0° warmer than a year ago. Only immediate lakeshore areas are unlikely to hit or exceed 80° Tuesday thanks to easterly winds off chilly lake waters.
-By Tom Skilling, WGN-TV Chief Meteorologist

An unusual high pressure blocking pattern has established itself over the eastern Great Lakes. Clockwise flow around this high will foster easterly winds over southern Lake Michigan and northeast Illinois. This rotation will carry warm Midwestern air into southeastern Canada and then rotate that air mass over land around to the south and finally west back into the lower Midwest. This pattern will recycle warm air and cut off moisture, leaving Chicago with a work week featuring only minor day-to-day temperature changes and low humidity.
The top thin layer of soils may start to show a little stress this week, but soil moisture calculations by the Midwest Regional Climate Center indicate that overall moisture values just below the surface are actually running a little above normal to a significant depth over northern Illinois. Meanwhile, this week the stagnant weather pattern will prolong the siege of severe weather over the southern and central Plains.
--By Paul Dailey, WGN Weather Center Meteorologist

A strong blocking pattern aloft will hold low pressure systems to the west; and when they move, is expected to steer showers and thunderstorms well to the south of Chicago during the week ahead. With persistent high pressure centered just to the east, surface winds will have an easterly component much of the time. The off-Lake Michigan flow will be light; muting the extent of the normal cooling impact. As a result daily high temperatures away from the lake should reach well into the 80s with 70° highs for the most part restricted to areas in the vicinity of the shoreline. Indications are the strong blocking pattern aloft will persist through next weekend, finally giving way to a cold front early the following week.
Saturday there were numerous severe t-storm reports,most occurring in New Mexico, Texas and Oklahoma. Three tornadoes were reported in the northern New Mexico counties of Sandoval and Santa Fe.
--By Paul Dailey, WGN Weather Center Meteorologist

Anson Mount shares this view of damage from Thursday night/Friday morning's storm complex taken at a hangar entrance at Waukegan Airport. The Airport measured well over 2" from the storms and wind gusts topped 45 m.p.h. Thanks for sharing this with us, Anson!
--Tom Skilling, WGN-TV Chief Meteorologist

Photo courtesy: Anson Mount

The 13th weekend here since meteorological spring began March 14 opens Saturday with Chicago at the calm heart of a high pressure predicted to begin warming Sunday—the first stage of a transition to a warmer, more humid weather regime next week. Much of the air movement at the heart of a high pressure system takes place vertically. Air sinks rather than moves horizontally as wind—and what wind blows tends to be disorganized (of varying directions) and will likely fade away in the coolness of night. Seasonable temperatures result—though more southerly winds will take hold Sunday afternoon.
In a final assault before lifting north and away from the U.S., the huge storm responsible for unleashing a 4-5 hour wind-driven, lightning-punctuated deluge Thursday across north suburban Lake and McHenry counties, spawned thunderstorms to Chicago’s east across 18 states Friday. Hail up to 4.25” in diameter crashed earthward from thunderstorms as they raced across Ohio. By late Friday evening, NOAA tallied 292 reports of severe weather.
--By Tom Skilling, WGN-TV Chief Meteorologist

Powerful non-thunderstorm winds gusted past 50 m.p.h. Thursday propelling temps to the highest levels in 10 months and laying the atmospheric groundwork for severe overnight storms. The area’s highest gusts included 60 m.p.h. three miles off Chicago’s lakefront at the Harrison-Dever crib, and 53 m.p.h. in downtown Chicago.
Readings topped out at 92° at Midway and 91° at O’Hare—at a time of the year when 77° is considered normal. Gary’s high of 93° was the metro area’s highest. The heat came on the heels of the city’s largest two day June temp increase in 21 years. T-storms, featuring dramatic cloud to ground lightning displays (up to 1,500 of them within a 225 mile radius of Chicago in a single ten minute period just after 9 p.m. Thursday evening), erupted suddenly late Thursday evening to Chicago’s west. Reports of funnel clouds and wind damage were widespread from the Quad Cities to Rockford.
--By Tom Skilling, WGN-TV Chief Meteorologist

Wall clouds, like the one picture here near Rockford late Thursday, are low hanging cloud formations often near the southwest quadrant of powerful thunderstorms beneath which tornadoes often spring to life. These photos, taken just before sunset and relayed to us by Scott Lasker and Brad Bartley, accompanied a powerful northeastbound cluster of thunderstorm—one of several which flared in north-central Illinois Thursday and proceeded quickly into Wisconsin.

Far more numerous thunderstorms flared later Thursday evening knocking out power around 9 p.m. on the west side of Davenport Iowa, and shortly afterward prompting reports of funnel clouds near Rock Falls, Morrison and Tampico, Illinois in Whiteside County.

Explosions of power transformers were so numerous, a National Weather Service-trained spotter reported they appeared to "light up the sky" east of Dixon, Illinois. Trees and power lines were reported down in storm gusts which raked Sterling. Gusts reached 60 m.p.h. at Mt. Morris. The late night storm eruption prompted the issuance of a tornado watch which included a large swath of the Chicago area through 5 a.m. Friday morning.

Our thanks to Scott Lasker and Brad Bartley for sharing the amazing wall cloud photos with us!

-Tom Skilling

Photos courtesy: Scott Lasker and Brad Bartley

A tornado watch has been issued for an area just west of the city of Chicago—including Lee, DeKalb, Ogle, Kane and McHenry Counties----until 12 midnight. The weather situation unfolding Thursday in the Chicago area and across a wide swath of the Midwest is a potentially dangerous one and threatens a powerful one-two meteorological punch---powerhouse 50+ mph non-thunderstorm wind gusts this afternoon and evening followed by strong, possibly severe thunderstorms, which could include scattered tornadoes, over at least sections of the metro area Thursday night. Non-thunderstorm straightline winds have been raking the area for hours and have already downed tree limbs and created damage. Peak velocities as recorded at 47 of the 153 Chicago metro area WeatherBug wind sensors have already exceeded 45 mph—including a gust of 51 mph at the LaSalle Bank building in downtown Chicago, 48 mph East Chicago and a number of sites within the Chicago city limits proper, and 45 mph Buffalo Grove, 44 mph at Gary and Hammond, IN, Kankkee and Oak Lawn, Il. The Harrison-Dever Crib three miles off Chicago Lake Michigan shoreline has been hit with 60 mph gusts. The winds sweeping the Chicago are projected to grow stronger this afternoon by a series of computer models, gusting to 50+ mph in additional areas before the afternoon and evening conclude.

Of equal and perhaps greater concern is the potential for damaging—in some cases possibly tornadic----thunderstorms Thursday night. As always, these storms may hit one area harder than another. But powerful thunderstorms may sweep at least sections of the greater Chicago metro area---which we are defining quite broadly as the the area extending from DeKalb and Rockford on the west to LaPorte and Rensselaer, IN to the east and south between 7 p.m. and 3 a.m.---arriving earliest at the western end of the metro area first then reaching eastern sections of that area late in the 7p.m. to 3 a.m. time frame. It’s possible few blustery t-storms may pop up in later this afternoon or early evening in advance of the primary severe weather period. But, a “cap’---a warm air layer aloft which interferes with updrafts of air which would otherwise produce t-storms in the hot 90-degree ground-level air mass currently in place---is likely to initially quell a large number of storms from forming in the afternoon and early evening period.

Wind advisories cover the entire Chicago metro area through midnight and the Storm Prediction Center has issued a rare “moderate” to “high” risk assessment as wekll. Sections of 25 states are under one form of weather advisory or another related to a mammoth storm draped across the Nation’s Heartland and centered in North Dakota.

Driving all features of Thursday’s wild weather is what amounts to a winter-intensity storm with a 978 mb (28.88”) central pressure superimposed of a hot, humid and therefore energy-rich summerlike air mass. The two don’t mix well and can encourage explosive severe weather development. The heat and humidity provide the fuel for thunderstorms at the same time increasing the rate at which temperatures decline with height. The heated air grows buoyant in this environment and rises forming towering cumulonimbus clouds (thunderheads) capable of gushing powerful straightline winds down to the surface and spinning up potent twisters. Meantime, the shear (wind speed and directional changes) created by powerful jet stream winds end up rotating the storms, creating supercells (rotating thunderstorms) in the process.

By definition, a “moderate” risk assessment from the Storm Prediction Center, in place across an area from eastern Oklahoma north across all of Wisconsin and the U.P. and extending into western sections of Lower Michigan—the entire Chicago area is included----Thursday night, suggests the threat of at least 30 reports of 1+” diameter hail and the potential for 6 to 19 reports of tornadoes somewhere in the outlooked area. The high risk area from north-central and northwest Illinois (including an area from Rockford west to Galena and Dubuque) and much of the eastern three quarters of Wisconsin is threatened with at least 20 tornadoes—including two of potential Enhanced Fujita Scale ratings of 3 or greater (indicating vortex winds of 136-165 mph).

The one wildcard in this severe weather situation—and it’s not insignificant—is the warm air aloft—the so-called “cap”. Computer models break this down, allowing severe storms to develop. Should the cap prove stronger than currently predicted, storms wouldn’t occur in the numbers of intensities feared in a worst-case scenario. Future weather statements should be monitored carefully. As of the 3p.m. posting of this update, intense t-storms are developing in a series of lines across Iowa, Missouri, northeast Iowa and western Wisconsin Doppler Scanned to heights of 60,000 ft.

Issued 3p.m. Thursday afternoon
Tom Skilling
WGN-TV Chief Meteorologist

A weather report from WGN Weather Center graphic artist Nelson Taruc:

About noon today, I heard a strong cracking sound in front of my house in northeast Oak Park. At first, I thought it was the high winds damaging a gutter. However, when I went to the front of the house to investigate, I saw that a tree had been blown over onto two houses across the street.

Given the notable strength of today's winds, I suspect that this will be just one of numerous examples of wind damage reported across the Chicago area.

Due to a very intense low pressure center in northern Minnesota, the National Weather Service Storm Prediction Center has forecast a moderate risk for severe storms today and tonight over much of the western Great Lakes and Midwest. High Wind Advisories have been posted for that same area today. Chicago’s greatest risk for severe storms will be between 6 p.m. and midnight. The cold front associated with this strong low center will move east of Chicago Friday morning followed by much cooler, less humid high pressure. At press time Wednesday evening, a total of four tornadoes had been reported in South Dakota, and Wyoming. A good portion of Wednesday evening’s severe weather centered over South Dakota with several large hail reports and a severe t-storm in White River that sustained 70 m.p.h. winds for 20 minutes. Earlier Wednesday, 92 m.p.h. wind gusts were recorded in Eagle, Colo.
-By Paul Dailey, WGN Weather Center Meteorologist

Furnaces will be firing up on Wednesday morning as temperatures bottom out in the chilly middle 40s, but in a little more than 24 hours the hum of air conditioners will be heard.
After Tuesday’s 64° high, the coolest here in nearly three weeks, readings will soar into the lower and middle 90s Thursday as strong south winds in advance of a “winter-strength” storm system, propel heat and humidity into the area.
This hot air blast will set the stage for a round of severe thunderstorms Thursday night into Friday morning before cooler and less humid conditions arrive.
Tuesday’s cool, showery weather was triggered by a sluggish upper-level low parked above the Midwest that has produced rain here every day so far this month. This system has produced numerous cold air funnels the past few days, and another one was sighted in Ogle County near Rochelle Tuesday.

--By Steve Kahn, WGN Weather Center Meteorologist

Summer rains are never evenly distributed, varying widely from spot to spot. But the downpours which walloped sections of northeast Illinois and northwest Indiana Monday deposited more than an inch of much needed rainfall at several locations while pushing O’Hare’s June rain tally to 0.63”. Mundelein was hit by 1.43” and Waukegan 1.34” Monday. June’s opening four days now rank 30th wettest of the past 137 years—a welcome development after May’s critical rainfall finished half (53%) normal. At Midway Airport, the June 1-4 period has generated 0.94” making it the wettest June open here in 8 years and the 13th wettest at the South Side site since measurements began there in 1928.
Cold air aloft encouraged air to rise and led to several reports of cold air funnels, principally south of the city near Kankakee, Illinois and Highland, Indiana. None touched down nor was there any damage reported.
---By Tom Skilling, WGN-TV Chief Meteorologist

Tribune photographer John Smierciak shares these shots of Monday's drenching downpours in the south suburbs and northwest Indiana. Real time WeatherBug network rainfall measurments indicates rainfalls in the day's downpours have exceeded 1" at a number of locations. Among the heavier reports through 3pm: 1.94" fell in Vernon Hills, 1.40" Mundelein, 1,21" Waukegan, 1.17" Libertyville 0.93" Lake Zurich and 0.78" at Griffith, Indiana. National Weather Service Doppler radar scans of cloud tops indicate some cells which towered to 43,000 ft. Little wonder such heavy rain fell and that lightning accompanied some of Monday's storms! Thanks for the great shots, John!

Tom Skilling

Photos: Courtesy John Smierciak, Chicago Tribune, South suburban/northwest Indiana shots

Monday promises to be damp and rather cool in Chicago with frequent showers and a few thunderstorms, compliments of a sluggish upper-level low pressure system meandering over the Midwest. This system produced scattered showers and thunderstorms across the region Sunday, bringing a brief but heavy downpour to Midway Airport in the predawn hours where 0.51” fell in just 15 minutes. More thunderstorms erupted Sunday afternoon with 0.41” falling at Waukegan accompanied by wind gusts to 41 m.p.h., while more than an inch of rain soaked portions of Kenosha.
With the upper low stalled over the area, more inclement weather appears on tap for Monday, but precipitation coverage and amounts could increase here as moisture from once-Tropical Storm Barry feeds into the system. Barry has been a prolific rain producer since it moved inland in Florida’s Tampa Bay region Saturday, bringing up to 6 inches to areas from Florida to Virginia.
--By Steve Kahn, WGN Weather Center Meteorologist

For the most part showers bypassed the Chicago area Saturday, but are expected to return on Sunday and Monday as an upper air disturbance drifts across the Midwest. Showers and thunderstorms are again forecast later in the week heralding both the arrival and the departure of a blast of hot and humid air that should send temperatures surging into the lower 90s here on Thursday.
Rain did not bypass Florida Saturday as Tropical Storm Barry moved onshore in the Tampa Bay area. The infant hurricane season’s second named storm, now downgraded to a tropical depression, brought wind gusts to 55 m.p.h. to the Clearwater Beach area Saturday, while bringing welcome heavy rainfall. Since Friday more than 6” of rain fell at nearby Largo while Dunedin measured 4.63”. In less than 24 hours, the soaking rains cut the area’s substantial year-to-date rainfall deficits in half.
-By Steve Kahn, WGN Weather Center Meteorologist

Friday afternoon and evening’s lightning-packed, wind-gushing thunderstorms raced across the Chicago area at 45 miles per hour after a vicious 800-mile 24-hour-plus trek out of the western Plains. Rare is the squall line able to survive over such a long period of time. After unleashing a swarm of as many as 13 twisters around midday Friday—tornadoes which hit areas just west of the Quad Cities with building-flattening force—the squall line took nine hours to cross northern Illinois, where its clouds towered to 52,000 feet, and 40+ m.p.h. gusts blasted Chicago’s west/northwest suburbs. Gusts to 60 m.p.h. were clocked at Kane County’s Maple Park, 54 m.p.h. at Naperville, and 44 m.p.h. at Lombard. Over a single hour Friday afternoon, cloud-to-ground lightning flashed more than 3,000 times. Rainfall fell so heavily in the Sterling/Rock Falls area of northwest Illinois—1.67” in just 30 minutes—serious flooding resulted. The Rockford area was drenched by 1” of rain.
--By Tom Skilling, WGN-TV Chief Meteorologist

Thanks to Kim and Bill Toth who captured these dramatic pictures of this evening's squall line as it raced through far northwest suburban Hampshire in northern Kane County around 6:45 p.m. Nearby WeatherBug wind sensors at Union and Burlington, Illinois both reported wind gusts to 45 m.p.h.
--By Steve Kahn, WGN Weather Center Meteorologist

Tornado watch issued for Chicago’s western suburbs, powerful storms may ultimately sweep into city toward Friday evening and night

A tornado watch has been issued for north-central and northwest Illinois—including western counties of the greater Chicago metropolitan area----until 7 pm this evening. Other sections of the Chicago area—including the city itself—could be at risk for active and possibly severe thunderstorms later this evening until around midnight Friday night if these storms hold together. Issuance of this watch by the National Weather Service’s Storm Prediction Center indicates developing atmospheric conditions support severe thunderstorms and possible tornadoes in AND NEAR the watch area. Humid air heated by Friday afternoon’s sunlight and twisted as it ascends into rotating supercell thunderstorms by powerful jet stream winds aloft are the driving forces behind a powerful eastbound squall line churning as of mid Friday afternoon across western Illinois. Radar scans of cloud top heights indicate the strongest these storms tower to heights of 47,000 ft.. Only the most vigorous thunderstorms grow to such heights. Several computer models, among them our in-house RPM (Rapid Process Mesoscale model) suggest these storms could hold together as they sweep into at least sections of extreme northeast Illinois between 7 and 10 p.m. Thunderstorms could last until midnight or shortly after.

Chicago area counties currently under a tornado watch until 7 pm include;

Boone, DeKalb, Kane, LaSalle, Livingston, Winnebago, Ogle, Lee, Kendall Grundy and McHenry.

Tom Skilling