Midwest Overview - September 1-7, 2002

The first week of September was generally dry and sunny in most of the Midwest, but was marked by two serious convective outbreaks in the northern Midwest. The first event, on the 2nd, produced a squall line with an F-3 tornado in Wisconsin, while the second event, on the 5th and 6th, brought flooding rains to the same vicinity. The total precipitation map for September 1-7 (Figure 1) shows a wide areas of east-central Minnesota and west-central Wisconsin received 3-6 inches of rain, areas around this received 0.5-1.5 inches, and the rest of the Midwest received little rain. The majority of the Midwest received less than 25% of normal rainfall for the week, while parts of Wisconsin received more than 500% (Figure 2). Temperatures were very warm in the northwestern Midwest, with Minnesota being 5-10°F above normal (Figure 3). The Ohio Valley was also quite warm, 4-6°F above normal. However, most of the central Midwest was closer to normal, only 2-4°F, due to cool evenings under very dry conditions. The drought severity in the Ohio Valley increased to severe levels along the Ohio River and in eastern Ohio (Figure 4, National Drought Mitigation Center). Corn crops are past the point of needing moisture now, but the soybeans have been hurt by recent dryness.

The town of Ladysmith, WI, was struck by a tornado at about 4:30 PM on September 2. A supercell storm formed at the end of a line of storms (Figure 5, U of Illinois Dept. Of Atmospheric Science); the rotation signature on the NWS Minneapolis radar showed winds greater than 50 knots in opposite directions at a high level in the storm (Figure 6, University Corporation for Atmospheric Research). During the 30-minute period that the tornado was on the ground, it traveled around 15 miles. The path reached a width of one-quarter mile at its widest point, and an F3 intensity right in Ladysmith. The central business district and at least 60 homes were destroyed, leading to an initial damage estimate of $20 M. Fortunately, no one was killed, but more than 60 people were treated for injuries at the hospital. The governor of Wisconsin has issued a state disaster declaration to allow the used of National Guard troops and equipment and free-up other resources for the effort. A federal disaster declaration has been requested. The clean-up efforts were hampered on the 5th and 6th when extremely heavy rains fell in the same area, as the jet stream continued to ride over the northwestern Midwest. The radar estimates for rain totals in some places exceeded 15 inches (Figure 7, National Weather Service), as storms trained over the area for more than 24 hours. The rain totals reported by the real time observers on the ground were only 4-5 inches in places, very significant but not quite to the level of the radar estimates. Flash flooding occurred in some rural areas, but receded quickly. However, the combination of storms and rain was not good for the crops, encouraging lodging in corn and various fungal diseases in soybean.