April 2001
Temperature and Precipitation Anomalies.
April 2001 was an important month in the climate history of the Midwest. A combination of rapid melting of the heavy winter snow pack and tremendous rains in April in parts of Iowa, Minnesota, and Wisconsin resulted in severe flooding along the Mississippi River that in places exceeded the levels of the great flood of summer 1993 (Figure 1). Despite the heavy flooding, however, the Midwest had only its 38th wettest April. This dichotomy is explained by the rapid onset of drought in the southern and southeastern Midwest in April, which missed all but one of the heavy rainstorms that afflicted the northwestern Midwest during the month. While Minnesota had its 2nd wettest and Wisconsin its 3rd wettest April, Kentucky had its 10th driest April on record. Precipitation totals exceeded 200 or even 300% of normal in most of Minnesota and northwest Wisconsin, but remained below 50% of normal in southern Missouri and eastern Kentucky (Figure 2). While the southern Midwest did receive some rain, these 1-2 inch totals were 2-3 inches less than normal, causing serious problems with early season crop germination (Figure 3). Midwest temperatures were also well above normal, resulting in the 14th warmest April and enhanced evapotranspiration in the driest areas. Only the areas frequently visited by storms in the northwestern Midwest were at normal or cooler than normal temperatures for the month (Figure 4).
A large cluster of thunderstorms passed through Missouri, southernmost Illinois, and southwestern Kentucky on April 3, leaving behind substantial rain and some damage (Figure 31, Storm Prediction Center). Hail of up to 2.75 inches in size and winds past 60 mph were reported, along with considerable flash flooding, from Kansas City all the way to Illinois. The storms also disrupted voting in some municipalities having local elections in Missouri, with voters having access problems due to flooded streets, road closed, and some tree falls and electrical outages.
April 10 and 11 were also very busy days for severe weather. On April 10, a series of thunderstorms traveled in almost a straight line parallel to I-70 from western Missouri to eastern Illinois along a stationary frontal boundary (Figure 32, Storm Prediction Center). While a series of weak tornadoes caused some damage, including heavily damaging a 36 unit condominium complex, the biggest impacts were associated with massive hail stones up to 3.0 inches in diameter that struck the northern suburbs of St. Louis. By the next week, 38,000 claims had been filed with the 5 largest auto insurers in the area, representing 56% of the total number of insured vehicles. State Farm, the largest auto and home insurer in the area, reported a preliminary insured loss of $95 M due to auto and home damage only. At Lambert International Airport, 22 TWA passenger jets were damaged to the point of requiring repairs. On the 11th, 36 tornadoes touched down all over Iowa and its boundary regions. The center of the small town of Agency, IA, was destroyed by a significant tornado, resulting in two deaths and several serious injuries. An Odd Fellows Lodge and 50 residences were heavily damaged or destroyed by an F1/F2 tornado. A great deal of damage occurred elsewhere during the outbreak.
A completely different kind of severe event occurred in northern Minnesota and Wisconsin in the Duluth area on April 23, when a severe ice storm stuck the region around Duluth with more than 0.5 inches of ice on trees and power lines. More than $5M damage occurred in Duluth alone, where more than 7,000 customers lost power and almost everyone lost trees. A further complication to the residents were that many who lost power also lost their sump pumps, and suffered basement flooding due to record rains that had fallen in the Duluth area during the month of April.