SEVERE WEATHER UPDATES: July 2007 Archives

As of 4:55 pm, severe thunderstorms have hit hard across the west and northwest suburbs. At west suburban Sugar Grove, winds were clocked at 60 mph along with torrential downpours. In McHenry county's Marengo, lightning struck a 4 foot diameter tree, knocking it onto the road at U.S.-20 and IL-23. More storms are possible as the most of the Chicagoland area is under a severe thunderstorm watch until 9pm. In addition, Dekalb county remains under a flash flood warning until 7:45 pm. due to 3-4" rains which fell yestersday along with new heavy rainfall today.

Bill Snyder
WGN-TV Weather Producer

Powerful eastbound thunderstorms are pounding the same areas west and north of Chicago Tuesday hit hard by thundery rains yesterday. The storms are headed toward Chicago. Powerful wind gusts accompany the 55,000 ft. tall thunderstorms and are sending temperatures plummeting. Readings beneath these storms have dropped nearly 20-degrees--from pre-storm mid 80s to mid to upper 60s once the rains commence and strong winds hit. Gusts of 43 mph have swept Waukegan as of 4:10 pm and 39 mph gusts have been clocked by WeatherBug sensors in DeKalb where another 0.65". Our live cameras there indicate visibility has dropped to zero in the downpours. The same is true near the Illinois/Wisconsin border at Algonquin.
The humid atmosphere is in an explosive state again as a cold front races across the area. Dangerous lightning accompanies the storms. Nearly 1900 cloud to ground strokes have been recorded in just the past 10 minutes (as of 4:15 pm) within a 225 mile radius of Chicago.
The latest squall line is much narrower than Monday's suggesting the storms will hit hard, last an hour then depart. A severe thunderstorm watch is in effect until 9pm this evening and indications are the last of these storms will depart Chicago's northwest Indiana suburbs before midnight. The cold front behind these storms promises relief from the heat and humidity the remainder of the week--though a few thunderstorms can't be ruled out later Thursday and later Saturday.
Of great interest here are continuing indications a lobe of hot air of the vast western hot air mass is headed toward the Midwest next week. We plan more coverage of that on our television weather programs and here on our weather blog later this evening and on our Chicago Tribune weather page at the back of the Metro Section Wednesday.

Tom Skilling
Chief Meteorologist
WGN-TV

Thunderstorms are drenching the DeKalb area this afternoon with 3.02" of rain down so far just before 5:00 p.m. Most of this rain has fallen in just a one hour time frame. A flash flood warning remains in effect for DeKalb county until 8:30 p.m. this evening. As much as four feet of water is reported on area roadways stranding many motorists.

Latest reports from the automatic surface weather observation station (ASOS) located at the Taylor Municipal Airport in DeKalb County
3.02” from KDKB ASOS in a little over 1 hour

2.94” in one hour 3:45p until 4:45p

Other information from the National Weather Service
City of De Kalb: Numerous roads closed due to high water
NIU Campus: Cars stalled in high water
City of De Kalb: Unofficial reports of 4 feet of standing water
Co-op Observer ESTIMATES 3.50” in a little over 80 minutes

Mike Hamernik and Steve Kahn WGN-TV Weather Center Meteorologists

Monday afternoon's thunderstorms brought an abrupt end to a hot, steamy day here. Outflow from the thunderstorms brought a rush of dense cold air to the surface dropping temperatures nearly 30º in less than an hour's time. The heat relief is only temporary, however, with heat and humidity expected to return Tuesday, along with more thunderstorms.

Here are some of the largest temperature drops as recorded on our WeatherBug network.
Hoffman Estates 93º down to 64º a drop of 29º
Wilmette 94º down to 66º a drop of 28º
Algonquin 92º down to 67º a drop of 25º
Chicago Lincoln Park 96º down to 72º a drop of 24º
South Elgin 92º down to 69º a dop of 23º

Steve Kahn WGN-TV Weather Center Meteorologist

The National Weather Service office in Lockport reported that the tornado sirens were sounded in Belvidere, Illinois earlier this afternoon based upon a funnel cloud sighting by a police officer. The funnel cloud quickly dissipated after the sirens sounded and no tornado warning was issued.

Mike Hamernik and Steve Kahn WGN-TV Weather Center

Heat/humidity provoking severe weather outbreak Monday afternoon; severe thunderstorm watch covers Chicago

A significant outbreak of downpour and lightning-generating severe weather is to sweep much of northern Illinois and Indiana Monday afternoon and evening and has already hammered much of southern Wisconsin and Illinois counties adjacent to the border. A severe t-storm watch covers the Chicago metro area until 8 pm. Our WeatherBug sensors have indicated 57 mph wind gusts have just hit Kenosha, Wisconsin (at 2:55 PM) and 40 mph gusts have raked Burlington, Wisconsin in the past half hour. Rainfall there has totaled 0.90" while 1.04" is down in Kenosha. Sirens are reported sounding in Belvidere based upon an unofficial tornado sighting in the area according to WREX in Rockford. Based on the moisture saturated atmosphere (there's 1.76" evaporated in the air over Chicago) fueling the storm outbreak, there's every reason to believe significantly more rain than that will fall in storms now sweeping a wide swath of northern Illinois and that flooding may become an issue in parts of the area.
Radar is scanning cloud tops at 50,000+ ft.--an indication of these storms' power---- and our lightning detection system has just indicated an amazing 1,900 cloud to ground strokes have occurred in the past 10 minutes. (This update is being placed on our blog at 2:55 pm). The storms are dramatically altering temperatures. Readings have plunged into the 60s under the heavy storms after hovering in the low 90s.
The atmosphere is in an explosive, energetic state, more than capable of supporting storms into the evening. Converging winds along a southbound cold front at the surface produce upwelling of the hot, humid air into lift-inducing jet stream winds overhead. Monday's storms are the result and threaten to be severe in some sections. The downpours come in the midst of this area's 4th month of below normal rainfall in Chicago. Northern sections of the metro area have fared better in the rain department but may be overburdened by Monday's heavier storms.
The gusty, rain-cooled storm outflow from Monday's storm outbreak is likely to initiate new storm development and impact Chicago proper as the afternoon and evening proceed. And, though dramatic heat relief is occuring with these storms--cooling likely to hold into tonight---it's temporary. The cold front responsible is to head back north and put the area back in unstable warm, humid air again Tuesday---a development likely to support new storms tomorrow.

UPDATE

McHenry County flash flood warning, Doppler rain estimate: 3"

Storms sweeping northwest suburban McHenry County have deposited an estimated 3" of rain in a very short time period prompting a flash flood warning.

Tom Skilling WGN-TV Chief Meteorologist,
Steve Kahn and Mike Hamernik WGN-TV Weather Center