By Tom Skilling
Thursday morning's showers and embedded thunderstorms are the second of three distinct waves of precipitation crossing the area this week.
The first passed in a weakening phase early Wednesday. After drenching sections of Iowa with more than 3 inches of rain and western Illinois with 1 to 2.4 inch totals, Chicago-area tallies proved far more modest. Though a respectable 0.71 inches fell at Wilmington in Will County -- the first measurable rain there in 17 days -- and 0.56 inches came down in Naperville, other totals were far less impressive. O'Hare tallied just 0.17 inches and an equally unimpressive 0.13 was reported at Midway.
The rains don't appear to be over yet. How much actually occurs, and whether it falls again in active thunderstorms as a cold front swings by later this evening, depends a great deal on how warm it gets Thursday afternoon. That is dependent on how much sun breaks through the clouds in the wake of this morning's rains.
The four most recent "runs" of several key National Weather Service computer forecast models produce a huge spread in predicted rainfall. Projections covering the period which began overnight and continues through Thursday night, range from 0.3 to as much as 3.43 inches -- a large spread but not at all uncommon during the summer because of the role thunderstorms play. These storms can be quite selective in their rain distribution.
An average of the four most recent sets of computer rainfall estimates for the Chicago area comes in at 0.94 inches -- a clear indication there may yet be additional useful rainfall ahead of an unseasonably cool outbreak expected to spread into Chicago late Thursday night and Friday.
Temperature downturn may produce coolest daytime highs since May
Temperatures are likely to struggle just to get close to 70 degrees Friday. That would make it one of the coolest days here in months. If, as now predicted, back-to-back highs Friday and Saturday fail to reach 70, it would mark the first time since May 17-18 that Chicago's high temperatures have failed to break out of the 60s.
It won't just be the cooling predicted to occur Friday which is noticeable. The winds predicted to blow amid the temperature decline will be formidable too. Widely varied barometric pressures between a deep Canadian low pressure and an impressive early-season ridge in the Plains could set up gusts as high as 40 mph at times.
Hurricane Earl threat disrupts Labor Day plans
Hurricane Earl's top sustained winds increased to 135 mph Wednesday, strong enough to return the tropical behemoth to Category 4 status. Hurricane warnings were hoisted long the North Carolina coast while the risk that New England might be dealt a blow by Earl was on the rise prompting the issuance of hurricane watches. U.S. Navy models project towering 25+ ft. waves may flirt with North Carolina's Outer Banks as early as late Thursday night.
An in-house tally of U.S. hurricane landfalls each decade since 1950 indicates 44 have occurred in the 10 years since 2000 -- far and away the greatest number of any decade in the past half century.
