August 1-7, 2003
Midwest Weekly Highlights - August 1-7, 2003
The cool, stormy weather of July continued into the first week of August.
Average temperatures during the week ranged from 3 degrees above normal in western Missouri and north central Wisconsin to 1.5-2.0F below normal in a northwest to southeast band from southern Minnesota to southern Indiana and northern Kentucky (Figure 1). This band coincided with the western edge of a strong upper trough of low pressure that remained anchored over the eastern United States. Rainfall this week was heavy in the eastern half of the region, exceeding 300 percent of normal from northeastern Ohio through much of Kentucky. (Figure 2). Only scattered thunderstorms occurred throughout much of Minnesota, Iowa, and the northern half of Missouri. Much of northwestern Missouri remains in moderate to severe drought (Figure 3).
An active week began finding low pressure centered over southern Wisconsin on the morning of August 1 with a weak and slow-moving cold front trailing through Iowa, northwestern Missouri, and into Kansas. This cold front was the focus of heavy thunderstorms By late afternoon strong to severe thunderstorms had developed in northeastern Illinois, southern Michigan, northeastern Indiana and northwestern Ohio (Figure 4). The storms spawned one tornado in northern Illinois and four in northern Indiana. The main threat from the storms, however, was large hail and damaging winds, with many reports of hail one inch or larger (Figure 5). The storms were also heavy rain producers and urban street flooding added to rush hour woes. In the Chicago area about 65,000 Commonwealth Edison customers lost power due to the evening's storms. The storms also knocked out power to 20,000 Detroit Edison customers and 15,000 Consumers Energy customers in south central and southeastern Michigan. Severe thunderstorms also developed across southwestern Missouri during the afternoon and evening.
A cold trough of low pressure aloft drifted over the Great Lakes on August 2nd and 3rd. The cold air aloft combined with warm, unstable air near the surface was favorable for the development of thunderstorms during the afternoon and evenings. A line of storms developed just ahead of the cold front from Missouri through Illinois and into Indiana, and severe thunderstorm watches were issued for southern portions of the Midwest. Large hail and high winds were again the main threat. The storms were slow-moving resulting in heavy rain along their paths. On Sunday, August 3rd, thunderstorm began forming along the southern shore of Lake Michigan from >Chicago all the way around to >Muskegon, MI. Surface winds were very light across the region during the afternoon allowing a lake breeze to set up. The storms developed where the cooler air flowing in from the lake met the warmer, more humid air over the land. The result was a “ring of fire” around the southern tip of Lake Michigan, readily seen in both satellite (Figure 6) and radar images (Figure 7). The storms moved very slowly because of light wind speeds up through the mid levels of the atmosphere, and thus many areas received several inches of rain as the storms rained themselves out.By the time the weekend was over much of northern Illinois, eastern Indiana, southern Michigan, and northwestern Ohio had received two to four inches of rain, with some radar estimated amounts of 8 to 10 inches (Figure 8). The heavy rain was responsible for the collapse of a roof in Chicago, and storms left 32,000 Commonwealth Edison customers without power.
The cool, wet weather this summer is thought to have contributed to unusual swarms of gnats in the Chicago and Milwuakee lakefront areas early this week. The clouds of gnats bugged residents throughout the weekend getting into people's eyes, noses, and mouths. Entomologists at the Field Museum in Chicago suspected the annoying insects were various species of gnats and midges, which start their life cycle in water.
Meanwhile, there was little rain in western Missouri through southwestern Iowa. The heat from Texas through the central plains nosed into western Missouri where high temperatures reached the mid 90s for much of the week. Crop conditions have continued to decline especially in the western half of Missouri where precipitation since June 1 has been less than 75 percent of normal.
The Midwest enjoyed generally tranquil conditions on August 5-7, with temperatures near to below normal and scattered showers and thunderstorms throughout most of the region as a series of weak upper level waves rotated across the Midwest through the eastern trough. A few of the thunderstorms reached severe levels in Iowa, Missouri, and Wisconsin, causing some minor damage. Heavy downpours causing minor street flooding were not uncommon with many of the storms.