Southern Wisconsin and Northern Illinois
4:00 PM CST, April 2, 2003
A classic early spring weather pattern developed across the Great Lakes region
on Tuesday April 2, 2003. A "flat" ridge of high pressure settled across the upper
Great Lakes region, in an east to west orientation. A developing low pressure system was
gathering strength across the middle of the United States. |
Strong southerly winds ahead of the low were pumping warm air north (yellow arrows). Meanwhile, northeast winds circulating around the high (white arrows) were cooled considerably by the cold waters of both Lake Michigan and Lake Superior. Lake water temperatures were in the lower to mid 30s. It was a classic battle between the cold dense air trying to move south, as the warm air was flowing north ahead of the low.
The airmasses essentially reached a balance and resulted in a nearly stalled frontal boundry depicted in the image above in the zone of tightest temperature contrast.
Some notable temperature contrasts near the front:
Chicago, IL Lakeshore 450 while 40 miles inland Joliet, IL was 790