April 11-17, 2002: Spring Arrives, and then Summer.

The week of April 11-17 marked an abrupt transition from cool spring to warm summer-like conditions. Temperatures for the week were 14-18°F above normal in the northeastern quadrant of the Midwest, and greater than 8°F above normal elsewhere (Figure 13). The hottest days were on April 15-17; maximum temperatures averaged 30°F above normal for the three days in northern Michigan, more than 24°F above normal in all of the northeastern Midwest, and more than 15°F above normal elsewhere (Figure 14). The week started with the entry of a warm front into the Midwest on the 11th, followed by a low pressure center passing trough the upper Midwest on the 12th. The cold front boundary with the low stalled in the Ohio Valley, and provided the focus for more precipitation on the 14th and 15th. The two areas of precipitation exceeding 1.5 inches are easily seen on maps of the weekly precipitation (Figure 15). Precipitation exceeded several hundred percent of normal in the band from north-central Iowa to the UP of Michigan, and was more than 200% of normal in the band between southeastern Michigan and the Ohio Valley (Figure 16). There was no snow to report during the week. Some areas of the Midwest missed out on the substantial precipitation, including most of western and central Iowa, where moderate drought conditions remain (Figure 17, National Drought Mitigation Center).