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October 24, 2001 Severe Weather Outbreak
Severe thunderstorms and tornadoes are relatively rare during October in the Midwest. In Illinois, for example, only January and February have recorded fewer tornadoes than October. So the magnitude, intensity, and extent of the severe weather on this day were even more remarkable.
The surface weather map on the morning of October 24 depicted an intensifying low pressure center at the western tip of Lake Superior, with one cold front trailing south through Wisconsin, Mis souri, and into northern Texas (Figure 1). A second cold front extended from the low through northern South Dakota and back northwest through Montana. The 500 mb map that morning had a closed low centered over western Minnesota with strong troughing through the Central Plains. (Figure 2).
The Storm Prediction Center (SPC) Severe Weather Outlook issued shortly after midnight CDT placed the southern half of Illinois, all of Indiana, extreme northern Kentucky, and western Ohio in a high risk area for severe weather (Figure 3).
The SPC defines a high risk area as one that “almost always means a major severe weather outbreak is expected, with great coverage of severe weather and enhanced likelihood of extreme severe (i.e., violent tornadoes or extreme convective wind events over a large area). Within a high risk area, expect at least 20 tornadoes with at least 2 of them rated F3+, or an extreme derecho causing 50+ widespread wind events (50+) with numerous higher end wind (80+ mph) and structural damage reports.”
The line of storms intensified in eastern Illinois as it approached the home town of the MRCC, Champaign, IL (Figure 5).
A tornado was reported south of Decatur by the tower at the airport. At 1:35 p.m.CDT, 5 minutes before this radar image, a tornado was reported south of Monticello. An F2 tornado struck Monticello, IL shortly thereafter. The map below, prepared by the NWS, shows the location of the damage. Photos show some of the damage in Monticello (National Weather Service, Lincoln, IL), and F1 tornado damage on the north side of Champaign (MRCC, Steve Hilberg).
20 tornado, 72 severe hail, and 285 severe wind preliminary storm reports
were reported by the National Weather Service in the MRCC state coverage
region. and they were largely centered on the predicted area of highest
risk (figure 10). One
person was killed as a tornado collapsed her home near LaPorte, IN,
and another was killed in Michigan by straight-line winds toppling
a tree on his truck. At least another 20 were injured in Missouri,
Indiana, Michigan, and Kentucky. This was the strongest October
tornado outbreak in the Midwest since the famous outbreak of October
14, 1966, which formed 26 tornadoes predominantly in the western Midwest,
including an F5 in Wright County in north-central Iowa that killed
6, injured 172, and caused $25 million in damage.
Upper Midwest Hit by Snowstorm
The low pressure center associated with the strong cold front slowly moved north and rapidily intensified on October 24th. This low pressure center was named Al by the National Weather Service, becoming the first named winter storm of the season in the north-central U.S. As the low entered northern Minnesota, it was quite strong. The storm center intensified greatly overnight, creating tremendous pressure gradients over the northern Midwest (figure 11).
Due to high winds, blizzard conditions were common during the storm, and transportation was disrupted. Snowfall totals exceeded 6 inches generally in northern Minnesota, Wisconsin, and Michigan. The highest totals were measured at Hallock, (11 inches), Thief River Falls (11 inches), and Argyle (14 inches) in northwestern Minnesota, and in northern Wisconsin at Hurley and Mercer (10 inches). Lake effect snows occurred in northern Michigan as the storm pulled away, with Marquette, MI, setting new daily snowfall records on October 26 with 4.5 inches of snow and October 27 with 2.1 inches.