July 15-23, 2002: Heat and Dryness Impact Crops; Some Local Relief.

A mixed bag of searing hot days, heavy rain, and persistent dryness impacted various locations in the Midwest during July 15-23. The nine day precipitation total indicates some of the locations that received heavy rain, including parts of Minnesota, Wisconsin, Michigan, southern Missouri, and the Illinois/Indiana and Illinois/Iowa border regions (Figure 17). More than 1 inch of rain fell broadly in these areas, while some narrow zones experienced flash flooding and 3-6 inches of rain. Other areas of the Midwest missed out on the rain, especially southwestern Iowa and northwestern Missouri, northern and southern Illinois, southern Wisconsin and Michigan, and most of Ohio (Figure 18). These locations received less than 50% of normal rain in the middle of corn fertilization season, in addition to experiencing the cumulative effects of earlier dryness. The period temperatures were near normal in the southern Midwest and 2-7°F above normal in the northern Midwest (Figure 19). However, there were days with extreme heat at the beginning of the period on July 15-16 and another round of intense heat July 20-22 (Figure 20). A temperature of 104°F was recorded at Glenwood, IA, on the 22nd, and the summer heat-related death statistics increased by 4 to 24 in Chicago. The combination of heat and spotty rain resulted in most of the central and eastern Midwest continuing to deteriorate in terms of soil moisture and agriculture conditions, leading to an abnormal dryness designation in much of the region and worsening drought status in the western Midwest (Figure 21, NDMC).

Weather was more active during the 9 day period than in previous weeks, but the organization of convective systems was not uniform across that region. For example, a mesoscale convective system moved north to south along the Mississippi River on July 18, dropping 1-4 inches of rain along its path (Figure 22, National Weather Service - NWS). Even when lines of storms formed along a very slow moving cold front on the 21st (Figure 23, U of Illinois Dept. Of Atmospheric Science - UIUC DAS) and 22nd (Figure 24, UIUC DAS), some locations received torrential rains from training storms, while nearby places received brief periods of rain or none at all. The precipitation distribution depended on mesoscale features and the timing of the frontal passage at a particular location. For example, the Chicago area was missed entirely as the front passed on the 22nd before storm development took place. Some of the more significant frontal rainfall events with flash flooding and severe storms occurred in the northern Midwest from July 20-22 (Figure 25, NWS) and in central Illinois and Indiana on July 22-23 (Figure 26, NWS). The storms on the 22nd caused a nationwide back-up of air traffic traveling east-west through the Midwest, delaying some flights for many hours as air traffic controllers rerouted planes. Severe wind reports were especially concentrated in southeastern Michigan (Figure 27, Storm Prediction Center - SPC), where more than 40,000 electrical utility customers lost power.