By Tom Skilling
Powerful thunderstorms bypassed Chicago Monday -- and so did 90-degree heat. It marked the first time in six days the mercury failed to reach 90 degrees here and ended the area's longest string of consecutive 90-degree days in four years. Not since July 28 through Aug. 2, 2006 had the Chicago area logged more 90-degree temperatures than in the five days leading up to Monday.
Incredibly, July 2010, with an average temperature of 78.1 degrees on the books to date, is running 10 degrees warmer than the same period a year ago and nearly 5 degrees above the long-term average. Using temperature data as a guide, it appears air conditioner use for the month may be outpacing last year's usage by a whopping three and a half times!
The twelve 90-degree temperatures on the books this year is four times as many as had occurred by this time a year ago.
The more seasonable brand of warmth is to continue its dominance in the area Tuesday and Wednesday. Both days are likely to see highs in the mid 80s over the vast majority of the Chicago area. But a new round of 90-degree heat -- including the possibility of 2010's hottest temperature to date -- is in sight.
Just how hot late-week temperatures ultimately become will depend in large measure on the extent and timing of what are sure to be active late week thunderstorms. The timing of these thunderstorms later this week will be critical to warming. It's no accident that thunderstorms have been referred to as nature's great air conditioners. The unique height of thunderstorm clouds enables them to tap cold air aloft and carry it earthward in their rains.
Storms in Iowa, downstate Illinois; induce flooding, down trees, powerlines
Chicago's official July rainfall has slipped modestly behind normal for the first time this growing season. This is a frequent development at this time of the year in light of July's strong sunlight. It doesn't take long for lawns or plants to begin browning because July boasts the year's highest evaporation rates. More than 6 inches of moisture per month -- 1.5 inches per week -- returns to the atmosphere this month through evaporation. This makes regular rainfall critical, especially as the region's crops enter their critical pollinating stage.
What happened Monday south and west to Chicago's is illustrative of what may be on the way in coming days. Waves of southeast-bound thunderstorms erupted Monday from northwest Iowa to central Illinois subjecting that corridor to waves of torrential downpours which exceeded 4 inches at some locations.
As the dome of blisteringly hot air around which those storms flared expands farther north, thunderstorms like those observed Downstate Monday, are likely to expand farther and farther north.
While U.S. broils, deadly Antarctic chill grips southern and central South America
While heat advisories are out for sections of seven states in the U.S. and temperatures head to triple digit levels again in coming days, a blast of cold Antarctic air has turned deadly in south and central South America where the southern hemispheric winter is in full swing. Hardest hit has been Argentina where nine deaths are being reported because of the unusual chill. But sections of Brazil, Uruguay, Bolivia, Paraguay, Chile and southern Peru have also been affected. The chill sent temperatures in the Patagonia region of Argentina tumbling to just 7 degrees. Some locations in the region have recorded the coldest temperatures on record. Especially cold weather gripped parts of South America several years ago during the onset of a La Nina (a cooling of the equatorial Pacific which is also underway this year as well).
