July is off to cool start, averaging more than 5 degrees below normal. The month's first six days have come in at just 67.3 degrees, well short of the 50 year average of 71.6 at O'Hare International Airport. This makes the opening six days of July 2009 one of the eight coolest July openings since weather observations began on the Northwest Side in 1959. Monday's high of 86 degrees and the 81-degree high on Sunday provided quite a contrast to July's cool trend. Monday was the warmest day of the month to date.
But 80s aren't likely to be repeated Tuesday. The re-emergence of northeast winds off Lake Michigan brought on by Canadian high ridges southward into the Chicago area, pressure will slash Tuesday afternoon's highs by at least 12 degrees even as blistering heat expands into the Plains. The developing clash in coming days between the two widely varied air masses will promote the formation of thunderstorm clusters--expected to initially track to the west and south of Chicago, brushing the area with several showers Tuesday and Wednesday. But by Thursday, the growing dome of heat threatens to nudge storms farther north, potentially affecting Chicago.
Latest stats confirm summer among the coolest/wettest on the books here
The three month meteorological summer period, which gets underway June 1, has averaged 67.5-degrees--more than degree below normal and ranks among the coolest third of all summers on the books here since 1871. The 7.43 inches of rain nearly twice the 4.34 long term average and places the period since June 1 among the wettest 9% on the books.
