Fierce 70+ mph storm gusts down trees, knock out power to 250,000

Fast moving thunderstorms, some racing along at speeds up to 55 mph, swept the Chicago area in three distinct waves Friday. The second and third, which hit in the afternoon and late evening, were far and away the most formidable, producing spectacular lightning counts, damaging wind gusts topping 70 mph and downpours of more than an inch. While the first of the three waves passed in the early morning hours with just a few claps of thunder and spotty half-inch rain tallies, the afternoon and evening storms emanated from thunderstorms with Doppler radar-scanned tops more than 10 miles high.

The t-storms associated with Friday's first wave were the dying remnants of powerful storms, which only the day before (on Thursday), had produced more than six dozen reports of twisters to Chicago's west across sections of Iowa, Minnesota and North Dakota.

The storms which followed them in Chicago Friday afternoon and night were in an entirely different meteorological league--far more intense and damaging. The stronger late-day storm eruption was the product of 90-degree heat and a surge of stifling Gulf-level humidities which combined to fuel thunderstorm growth.

Storms intensify Friday afternoon
What happened in terms of storm intensification Friday afternoon was stunning. Cloud tops grew from just under 30,000 feet Friday morning across Iowa to nearly 60,000 feet with the addition of daytime heating as the storm complex moved into northern Illinois.

Lightning counts more than quadrupled between midday and the evening rush hour, exploding from 1,800 cloud-to-ground strokes in the hour leading up to noon to more than 7,500 discharges between 5 and 6 p.m.

The day's third wave of storms, which swept into the Chicago area late Friday evening, generated nearly 10,000 cloud-to-ground strokes during its peak hour around 10 p.m. as the late evening storm coverage expanded to include much of northern and central Illinois.

Damage reports surge as 70+ mph gusts blast many areas
By late evening, power was out to a quarter of a million Chicago area residents. Trees and tree limbs which had fallen across some area roads disrupted traffic flow while new waves of thundery downpours prompted flood warnings into the early morning hours Saturday.

In Chicago alone, the Department of Streets and Sanitation reported 1,100 trees down--some on top of cars. Sections of roofs were blown off several buildings in far west surburban Rochelle while powerful gusts flipped camper trailers in Belvidere at Outdoor World. Sections of Midwest Road in Oak Brook were blocked for a time by downed tree limbs, and trees were reported to be blocking some roads in the Algonquin and Barrington areas. 1 ft. diameter trees were reported down in sections of Franklin Grove while 6" diameter trees were on the ground near North Avenue and I-290 in Elmhurst.

The day's strongest storm gusts clocked at the Crib and Three Rivers, Michigan
While gusts hit 60 mph at O'Hare and 58 mph at Midway, Friday's strongest gusts were recorded at the Harrison-Dever Crib (77 mph) and at Three Rivers, Michigan (79 mph).

2010 Growing season jumps to third wettest in 82 years
The 2010 growing season--the period which began April 1--jumped to 3rd wettest of the past 82 years at Midway Airport late Friday when the rain tally reached 15.63". The 82-year average growing season rainfall to date (the period from April 1 to June 18) has been 9.71".