The Midwest will experience a substantial change in the airmass over the next two days. Gone will be the hot humid airmass that has tied or set numerous records over the past two days, to be replaced with a much more seasonal Canadian airmass. The graphic from the Chicago Tribune shows just how extensive the heat has been, and how hot the temperatures. Readings that are expected in mid July, not mid September. The hot dry weather has aggravated the rapidly developing drought over the western 1/2 of the Midwest.
As the graphic shows in the upper right, the change in weather is a product of a change in the direction of the jet stream. The upper level ridge that had been over the area is breaking down and moving west. This will allow the jet stream to come in from the northwest, bringing down the much cooler Canadian air. Hopefully, some storms will form along the front to provide much needed rainfall as the drought expands.
For the Chicago metro area, we are looking at 25-30 degree temperature drop from the Tuesday highs to the Friday highs. The official high the past two days for Chicago has been 95. This tied the record high for Tuesday, Rockford tied their record with a 96. We also set a new warm overnight low record. By Friday afternoon highs are only expected in the 65-70 degree range. Some storms are expected along the front late this afternoon and early tonight, but unfortunately no large or widespread rain amounts are expected.
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