Friday, September 25, 2020

November-like chill to overtake the Midwest and begin its trek through
the northeast for early October

By Alex Sosnowski, AccuWeather senior meteorologist

Autumn officially began on Sept. 22, but it certainly hasn't felt like it across the Midwest as unusually warm weather has been gripping the region this week. Forecasters say big changes are on the way, and the places like Minneapolis, Chicago and Detroit and many others may seemingly skip over the first part of fall and could be plunged into a November-like pattern next week.

The main culprit behind the dramatic weather changes will be the jet stream, which AccuWeather meteorologists expect to take a big southward dip over the central United States. That will send waves of chilly air more typical of November diving south from Canada. Some cooler air will eventually reach the Eastern Seaboard too, but it may be delayed and have much less punch when compared to blasts of crisp air headed straight for the Midwest. 

A more typical pattern for the jet stream during late September and early October would be more of a straight line, or west-to-east flow, that keeps weak storms moving along at a fast pace and brief alternating surges of warmth and doses of cool air. When the jet stream bulges more dramatically southward and northward like the setup predicted across the United States next week, cold air can advance well to the south in the lunges and surge well to the north in the bulges.

Thus, the clock is ticking on the latest surge of warmth over the Plains and Midwest that has brought widespread highs ranging from the middle 70s F to the middle 80s, averaging 5-10 degrees Fahrenheit above normal. The leading edge of the first push of cooler air in a series will sweep from the northern Plains on Saturday to the central Plains and part of the Great Lakes region during Sunday and Monday.

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