By Tom Skilling
The transition to the markedly cooler air predicted to dominate Midwest weather Friday and Saturday was a stormy one late Thursday.
Driving downpours cascaded from powerful thunderstorms responsible for spawning some damaging wind gusts exceeding 60 mph at harder hit locations, downing trees in the Elgin and Carpentersville areas and in some cases taking power lines down with them.
Geneva in the Fox Valley recorded 0.8 inches in just 20 minutes while 0.61 inches fell in a half hour at Northbrook near I-94 and Dundee Roads.
Those downpours marked the third wave of rainfall to sweep sections of the Chicago area in the past two days, collectively producing the most significant rain to occur in parts of the area in more than a month. Unofficial 2-day rainfall measurements at various WeatherBug stations by late Thursday topped 2 inches at Wilmette and Flossmoor (2.62), Winfield (2.18), Niles (2.16), Palatine (2.16), Glenview (2.05), Schaumburg (2.04) and Naperville (2.02).
Temps to stage strong rebound Labor Day, Tuesday
Despite the day's cooler temperatures, daytime heating will destabilize the atmosphere Friday. This will encourage cottony cumulus clouds to bubble up and ultimately produce a few comparatively brief, light rain showers in the afternoon and evening. Clouds fade Friday night and Saturday will remain cool under the day's all but cloud-free skies.
But warming isn't far off. Temperatures rebound to the mid 70s Sunday and to the low or mid 80s by Labor Day Monday.
Warmer than normal temperatures are likely to dominate next week and there is potential for an isolated warm frontal thunderstorm in a spot or two Sunday night/Monday morning. A more vigorous system with showers and thunderstorms is possible late Tuesday and again later in the week.
Wisconsin, Central Illinois walloped by thunderstorms
Afternoon storms, some with cloud tops 57,000 feet above local terrain, drenched sections of central Illinois and at the same time others pounded southern Wisconsin. All this took place before the Chicago-area's drenching evening cloudbursts arrived. The strongest of the storms produced formidable wind gusts. Jefferson, Wis., reported 60 mph thunderstorm winds while Sullivan, home base for the Milwaukee National Weather Service Forecast Office, was whipped by 46 mph gusts.
In downstate Illinois, a 2.5-inch downpour drenched Philadelphia near Springfield. The state capital proper logged 1.67 inches of rain, flooding sections of the city.
Elsewhere, numerous power lines were reported down across Bloomington and thunderstorm rains submerged some streets under as much as 2 feet of standing water late Thursday. Hailstones 1 inch in diameter pelted the area.
Hurricane Earl rakes North Carolina's Outer Banks
Weather of a more tropical nature made news on the East Coast late Thursday. Hurricane Earl's sustained winds trended lower all day as the northbound storm accelerated into cooler coastal waters, exposing itself to increasing wind shear as upper winds around it strengthened.
Earl's peak winds hit 145 mph early Thursday but lowered to 115 mph by late evening. A NOAA buoy measured formidable 35-foot wind-tossed seas offshore in the Atlantic 150 miles east of Cape Hatteras, N.C. Hurricane warnings remained in effect over eastern North Carolina and farther north near Cape Cod, Martha's Vineyard and Nantucket in eastern New England.
Air venting out the top of Earl migrated away from the hurricane and sank well to the north inducing "compressional warming" -- a process which led to record heat in Maine. There, Portland recorded a 93-degree high Thursday, the fifth consecutive daytime temperature of 90 or higher. The string ties Portland's record for the most consecutive days 90 degrees or warmer.
Earl will undergo further weakening as it races north along the coast, a region that will be battered by the storm's waves until it hits landfall as a non-tropical system in Canada's Maritime Provinces early Saturday.
