The dramatic upper level pattern change that was advertised a week ago is here. The below normal temperatures of roughly the past 45 days are being replaced by above normal temperatures. The graphic from UCAR shows a plot of the 500mb level data Sunday morning. Notice the broad closed contour over the center of the nation. This represents a broad high pressure area aloft with sinking air, which warms as it gets compressed during the sinking motion.
For the Midwest and the Chicago metro area, this late push of summer warmth will stick around for a while. The broad upper level high pressure or "ridge" is forecast to continue into next weekend. The center of the ridge is forecast to slowly move west by mid week but then back eastward into next weekend. The bottom line is continued above normal temperatures into next weekend. Quite a change from only two weeks ago when everything was below normal.
For the metro area is particular, rising temperatures through Tuesday. Highs today, Sunday, will be around 90 and then into the 90s Monday and Tuesday. The humidity will gradally rise, most noticeable on Tuesday. A weak cold front will move through Tuesday night with the chance of some storms, then a little cooler, 85-90 for the rest of the week. With light winds there will be some lakeside cooling. The normal high is now down to 82.
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