A temporary lull in the action-more storms building across northwest Illinois

One of the strongest thunderstorms to hit the Chicago area in recent years has moved out into Lake Michigan, but more storms are on the way and a currently firing up in northeast Iowa and northwest Illinois. The storms are forming along a strong warm front separating warm and humid air across the southern Midwest from cooler dry air to the north.

 

New severe thunderstorm watch being issued for all of northern Illinois

A new severe thunderstorm watch is being issued by the Storm Prediction Center in Norman, Oklahoma for much of extreme northern Illinois including the Chicago area. It will be in effect until 6a.m. Tuesday morning. the area of the watch extends from eastern iowa into northern Indiana and covers an area from I-80 north into extreme southern Wisconsin.

 

Thunderstorms tap energy of 100 mph jet stream, mixing damaging winds down to the ground

Thunderstorms erupting along a northbound warm front turned violent over sections of northern Monday evening. Damage was so extensive in Oregon, the Ogle County community was described as “looking like a war zone” in a storm report filed just after 9 p.m. with the National Weather Service. Semis were blown over near Rochelle close to the intersection of I-88 and I-39 while gusts at Maple Park in Kane County hit 70 mph.  Wind gusts hit 68 mph at O’Hare at 10:47 pm and reached 60 mph a bit earlier at Franklin Grove, between Rochelle and Dixon. Gusts of 50 mph swept DeKalb.

Truly rare 2.75-inch diameter (baseball ball size) hail lambasted Des Plaines just before 11 p.m. Breaking windows—while other thunderstorms peppered Batavia, Mt. Morris, Forreston and Morton Grove with hail—ranging from marble size to 1-inch or more in diameter.  Hailstones 1.5-inches in diameter (ping-pong size) pounded Streamwood around 10:30 p.m. and Skokie at 10:55 p.m. while 1-inch hail (quarter-size) was reported in South Elgin.

Doppler radar scans indicated the storms responsible towered 50,000 ft. into the atmosphere—-tall enough to tap the powerful jet stream winds and divert wind energy to the ground. The fast high speed winds also push storms along at a good clip which

Lightning was prolific. Up to 1,100 cloud to ground lightning strokes occurred in a single ten minute period at one point Monday evening.

Ferocious storms produced serious damage in sections of northwest Illinois as well. Large trees 3 feet in diameter were uprooted and toppled, taking down power lines as they fell in Milledgeville, south of Galena in Carroll County. The winds there also damaged out buildings. The downpours accompanying the storms prompted flash flood watches were issued from Freeport west into Iowa. 

Thunderstorms earlier in the day produced the brief touchdown of a small tornado downstate 2 miles southwest of Hillsboro, Illinois south of Springfield. No damage was reported.
    
A warm front and the northward flood of the season’s most humid air behind storm re-eruption-and it’s not over
 
Warm, humid winds, responsible for 80+-degree warmth across the southern Midwest Monday, ran head-long into cooler easterly winds across northern Illinois and southern Wisconsin setting the stage for the evening storm outbreak. When winds converge at ground level, the resulting pile-up of air encourages air to rise and cool in the atmosphere. A faster than usual decline in temperature with height further encouraged the process, resulting in the formation of towering thunderheads—referred to as cumulonimbus clouds by meteorologists.

An additional cluster of storms may traverse the area Tuesday morning, becoming less numerous and more sporadic as summerlike warmth reaches into all but far northern sections of the metro area by afternoon.  There southeast winds off chilly Lake Michigan may limit warming in areas from Waukegan and Kenosha and north—and still more storms may flare later Tuesday night into Wednesday morning.

Warmest April open on record
 
April has averaged 62.2-degrees to date–the warmest April 1-5 period in 140 years of official weather records. It’s a reading 19-degrees above normal and 22-degree warmer than the comparable period a year ago.

Severe thunderstorm now over Lake Michigan, hail and wind threat from this cell has ended, but more storms on the way

At 11:05PM, doppler radar indicates that the thunderstorm that produced damaging winds and large hail over Chicago’s northern suburbs has moved out over Lake Michigan.

The immediate threat from this particular cell has ended for northeast Illinois.

The atmosphere over the area remains rather volatile, and additional severe storms may develop over the next hour or two. 

In fact a new Severe Thunderstorm Watch has been issued for most of the Chicago area until 6AM Tuesday morning.

Below:  Severe Thunderstorm Watch for Northern Illinois, Northern Indiana and Southern Michigan until 6AM

    

Large hail threat until 11:15PM from the north side of Chicago, north to Highland Park

At 10:55PM, radar continues to show a dangerous and severe thunderstorm over northern Cook County and eastern Lake County.

This storm should move out over Lake Michigan by 11:15PM.

Tennis Ball (2.50″) sized hail and baseball sized hail was reported in Des Plaines between 10:45PM and 10:55PM.