April 18-24, 2002: Severe Weather and a Temperature Roller Coaster.

The unusually warm weather of mid-April continued into the beginning of the week of April 18-24 across the southeastern half of the Midwest. However, by April 18 cooler air was already penetrating northwestern sections of the region, and the leading cold front triggered severe thunderstorms in Minnesota and Iowa. The intrusion of the cooler air is evident in the temperature departure map for the week, where temperatures ranged from 8°F below average in Minnesota to 6 to 8°F above average along the Ohio River (Figure 18). On April 18 temperatures topped 90°F as far north as the southern Wisconsin town of Beloit. Among the locations setting records for the date was Moline, IL, with a high of 91°F; Moline also tied its record for the most number of days in April 90°F or higher, a total of 2. Peoria and Rockford, IL, also reached 91°F, setting new records for the date. Chicago's O'Hare Airport set a new record of 89°F. The warm weather also spread into Michigan, where Saginaw reached 87°F. The heaviest rainfall during the week occurred in a band centered on a line from Kansas City, MO, to Columbus, OH (Figure 19); most of the band of precipitation in the southern Midwest exceeded 200% of normal precipitation (Figure 20). After enjoying summer-like temperatures earlier in the period, residents of southern Minnesota and central Wisconsin were jolted back to the reality of spring on April 21-22 when a blanket of heavy, wet snow was deposited as a strong low pressure moved through the Midwest (Figure 21). Four to seven inches of snow was reported on the ground in central Wisconsin on the 22nd.