With strong low pressure to the northeast of Lake Huron and cold high pressure
sinking south out of Canada into Minnesota, north to northwest flow brings
unseasonably cool air into northern Illinois today. Very cold air aloft makes the air
mass unstable, with only a small amount of solar heating possibly triggering widely
scattered brief showers this afternoon. The most unstable conditions that produced
some 31 severe weather reports in Minnesota, Wisconsin and Michigan Saturday is
positioned farther north and east today.
BLOCKING PATTERN ALOFT CHANGES LATER THIS WEEK
The strong high pressure ridge that has brought record warmth to the west coast —
dozens of record highs were set from California to Washington Saturday—and the
large low pressure trough that has guided a cool northerly flow aloft over the Great
Lakes and Midwest will modify as it slowly drifts east in the coming days. By Thursday
a strong low pressure center is forecast to develop over the Southwest and the upper
Great Lakes low will be centered over the northeast U.S. This should bring significant
cooling to the west coast and allow a warm-up in Chicago by the end of the
workweek.
