Midwest Overview - May 22-31, 2003

The Midwest was cool and mostly dry during the last ten days of May 2003. Large parts of Minnesota and Iowa received less than 0.5 inches of rain for the period (Figure 1), with central Iowa precipitation values less than 25% of normal (Figure 2). Only parts of Illinois and locations on the northeastern and southeastern rim of the region were above normal in precipitation total. The dryness was somewhat welcome by farmers, allowing them to get into the fields and catch-up on delayed planting activities. In addition, temperatures were considerably cooler than normal (Figure 3), especially in the central Midwest, slowing plant development and reducing evapotranspiration. Therefore, the drought status of the region largely held steady with the previous week despite the lack of rain (Figure 4, National Drought Mitigation Center).

Even though precipitation was fairly sparse, two significant outbreaks of severe weather did occur in the central Midwest on May 28th and May 30th. During the initial event, a weak cold front evolved to form a trough line with little temperature change but some humidity change across its boundary. Even though moisture was not abundant, there was enough instability and directional shear with height to form supercell thunderstorms in Illinois. Numerous tornado observations were reported (Figure 5, Storm Prediction Center). One of the large supercells southeast of Peoria in central Illinois displayed a classic hook echo (Figure 6, National Weather Service). Numerous severe event reports were collected by the NWS during the afternoon and early evening on the 28th, but there were no reported injuries and damage was light. The outbreak on the 30th covered a similar area, but was much more intense (Figure 7, SPC). A strong low pressure system and cold front swept through the region, triggering many severe thunderstorms. Of the approximately 30 tornado reports in the Midwest that day, several were F1 tornadoes and two were F2 tornadoes. A pair of two F2 tornadoes spawned by the same storm stayed on the ground for 14 miles and 10 miles, according to NWS surveys conducted after the storm. The second F2 tornado was very strong when it destroyed seven businesses and damaged many other buildings on the south edge of Clinton, IL. The radar image of this storm displayed a hook echo as it reached Clinton (the southernmost cell in (Figure 8, College of DuPage), and a very distinct wind shift was seen at that location indicating rotation on the storm relative velocity image (Figure 9, COD). Damage in Logan County, IL, was estimated as at least $2M, and more damage than that occurred in Dewitt County, where Clinton is located. Golf ball and even baseball sized hail impacted Tazewell and Woodford nearby; State Farm sent a catastrophe team to handle the hail damage claims, expected to number more than 1,000. The Chicago area also had widespread but light severe weather damage and power outages.

Behind the storms, a very cold and windy air mass entered most of the Midwest. Numerous reports of wind gusts greater than 50 mph occurred in Minnesota, Wisconsin, and Iowa. At the end of this most violent May, large sections of Missouri (Figure 10, FEMA) and Illinois (Figure 11, FEMA) had been declared federal disaster areas in response to the massive outbreak of tornadoes earlier in the month. More than $13.6 M of public assistance in Missouri and $2 M of public assistance in Illinois had already been dispersed by the end of the month. About 5,500 individuals in Missouri and 600 individuals in Illinois have applied for relief. While no cost estimates were available for the tornado damage for the month, the damage due to dam collapse near Marquette, MI, reported last week has reached $102 M in losses to date. This was a dangerous and expensive May in the Midwest this year.