April 1-10, 2002: Winter Gives Way Only Slowly.

An April's Fool snowstorm ushered in the new month with substantial snow and cold air in the upper Midwest. Total precipitation for the April 1-10 period exceeded 2 inches in a storm track from southeastern Iowa to central Michigan (Figure 6), while most of western Iowa missed the precipitation again, receiving less than 0.5 inches for the period. Much of the Midwest was at or slightly below normal in precipitation, except for the band described previously and snowy areas to its north (Figure 7). The snowfall for the period fell in the first 5 days of April, following the track of the April 1-2 snowstorm through the Upper Midwest or falling in the lake-effect belts in northern Wisconsin and Michigan (Figure 8) . The entire region was below normal in temperature for the period (Figure 9). However, record cold at Ottumwa and Lamoni, IA, Quincy, IL, and Grand Rapids, MI, on the morning of the 4th gradually gave way to above normal temperatures later in the period. The dryness of western Iowa was reflected in an increase in drought status to D1, moderate drought, in the U.S. Drought Monitor (Figure 10).

After the cold start to the period, the high pressure center from Canada moved to the east, allowing a flow of warm moist air to arrive in the Midwest. A low pressure center moving northward from the Texas Panhandle joined an advancing cold front and brought copious rain to the central Midwest on April 7-8 (Figure 11, NWS). Dubuque, IA, set a daily precipitation record on the 7th, Rockford, IL, and Grand Rapids, MI, set records on the 8th, and Moline, IL, set calendar day precipitation records on both the 7th and 8th. The cold front accompanying the low kept temperatures near normal for a day, but the high pressure center quickly passed by, and warm southerly flow returned on the 9th and 10th. Overrunning warm, humid air resulted in copious rain in the northern Midwest on the 10th, setting records for precipitation that day in Duluth, MN, and Marquette, MI (Figure 12, NWS).