Temperature and Precipitation Anomalies.

The Midwest was extremely wet in October, with the regional precipitation total ranking as the 4th wettest in 107 years. For the month, Michigan set a new record for state average precipitation total, and precipitation ranked 2nd wettest in Indiana, 3rd wettest in Illinois, 7th wettest in Kentucky, and 8th wettest in Ohio. Up to 9 inches of rain fell along the axis of several storms that traveled through Illinois, Indiana, and Michigan (Figure 1). The entire states of Indiana received 5 inches of rain more than normal for October (Figure 2). The west-central Midwest missed most of the storm systems and moisture, and southwestern Minnesota received less than 50% of normal precipitation (Figure 3). October temperatures averaged 1-3°F below normal in all Midwestern states except for Ohio, but the departures were not large, leading the Midwest to a ranking of 34th coldest (Figure 4). Temperatures were closer to normal in the eastern Midwest due to the warm advection ahead of several storm systems. The harvest was slowed by rain in much of the Midwest, except for the western and northwestern portions, where abnormally dry conditions developed towards the end of the month (Figure 5, National Drought Mitigation Center). The first major snow storm of the year also hit the northern Midwest on October 23-24, with light snow continuing for several days near the Great Lakes. The October snow total was more than 10 inches in a number of places (Figure 6).

Extreme Events and Impacts.

Some severe weather was embedded in both the October 9-10 and 13-14 systems. A tornado rated at between F0 and F1 struck the Southwest Missouri State University in Springfield, MO, on the 10th. An area 100 yards wide and a mile long lost many trees, experienced roof and building damage, and also lost utilities. The roof of a shopping center was also severely damaged, causing several hundred thousand dollars in damage at that location alone. The rotating elements of the mesocyclone that spawned the tornado were clearly seen on radar (Figure 31, NWS). About five inches of rain fell in the area, complicating clean-up (Figure 32, NWS). On the 14th, strong storms passed west of Chicago, dumping 2-4 inches of rain on the area (Figure 33, NWS). Hundreds of homes were flooded in Lombard, Naperville, and Wheaton, many cars were covered with water, and some streets were converted to streams running 3-4 feet deep. The Golf Mill Shopping center in Niles had its skylights blown out by high wind, injuring 6, damaging 9 stores, and requiring the mall to be evacuated. About 18,000 customers lost electrical service in the southern suburbs of Chicago. O'Hare Airport on Chicago's west side set a new daily rainfall record for October 14 of 3.79 inches, and reached 40.83 inches of rain for the year-to-date, 11.72 inches more than normal for the time of year, and 5.01 inches more than the normal annual total.

An intense low pressure center passed through the northern Great Plains into the Midwest on October 24. A powerful cold front with strong upper air support moved rapidly from west to east across the Midwest, traveling through central Iowa early in the morning (Figure 34a, UIUC Dept. of Atmospheric Science), hitting eastern Illinois by early afternoon (Figure 34b, UIUC DAS), proceeding rapidly east through eastern Indiana by early evening (Figure 34c, UIUC DAS), and exiting the eastern Ohio boundary of the Midwest at midnight (Figure 34d, UIUC DAS). During its progressive movement, intense squall line development took place, propagating bow echoes, damaging winds, hail, and tornadoes. The intensity of the line reached a high level in eastern Illinois as it approached the home town of the MRCC, Champaign, IL (Figure 35, NWS), with an F2 tornado forming just upstream at Monticello, IL. The line was particularly intense during the afternoon of the 24th, with small bow echos in the squall line corresponding to locations with straight-line winds exceeding 80 mph and including embedded tornadoes (Figure 36, NWS). The severe weather outbreak was very well predicted by the Storm Prediction Center (Figure 37, SPC). Approximately 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 oval of highest risk (Figure 38, SPC). 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 M in damage. Due to both the excellent predictions and timely warnings, and also the somewhat weaker tornadoes, there were fewer casualties in the 2001 outbreak than during the 1966 October outbreak. 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.

At the same time the cold front was moving through the central Midwest, the low pressure center was dragging to the north and intensifying rapidly. The 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 (Figure 39a, UIUC DAS). The storm center intensified greatly overnight, creating tremendous pressure gradients over the northern Midwest (Figure 39b, UIUC DAS). 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) (Figure 40). 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. Warmer conditions melted the snow pack by the end of the month in all but the most shady forested areas, leaving November to start with a fresh slate.