November 2001
Temperature and Precipitation Anomalies.
The nine-state Midwest region reached an all-time maximum temperature record for the month of November. The monthly average temperature was 46.5°F, which is a full 1.5°F above the previous record set in 1931. Four states individually set records for the highest November temperature in the 107-year record: Iowa, Michigan, Minnesota, and Wisconsin. Iowa smashed its previous record for November by 3.1°F, while Minnesota exceeded its previous record by 2.5°F.
The Midwest was warm throughout its extent, with temperature anomalies ranging from +12°F in Minnesota to +4°F in Kentucky (Figure 1). The first three weeks of the month were also quite lacking in precipitation, causing portions of Minnesota and Iowa to become abnormally dry. However, precipitation levels recovered with a series of storms at the end of the month (Figure 2), and the Midwest had its 45th wettest November on record. Very large positive anomalies occurred in two bands, one from Iowa to northern Michigan, and one through the Ohio Valley (Figure 3). Minnesota had its 16th wettest November due to tremendous snowfall during the 26th through 28th that set some local records there and in Wisconsin and Michigan. Only west-central Missouri received less than 75% of normal precipitation for November 2001 (Figure 4).
On the 24th, an intense low pressure center entered the region from Nebraska, with overrunning precipitation and a cold front bringing significant rain to much of the Midwest through the 25th. Enough cold air was in place in the northwestern Midwest for the next strong low pressure center in the series to whip up a tremendous snowstorm, creating a band of 12 inch or greater snowfall amounts starting in Colorado and extending all the way to northern Michigan (Figure 25), NWS - Central Region Headquarters). Snow continued through the 28th in places, resulting in 30.4 inches of snow in Willmar, MN, and 30.3 inches of snow at the Marquette, MI, office of the National Weather Service. Both locations set new all-time records for snowfall total in any single day of the year. Willmar received 21 inches of snow from 8 AM on the 26th to 8 AM on the 27th, and Marquette collected 19.2 inches of snow on the 27th from midnight to midnight. Many individual stations near these two locations also received more than 20 inches of snow (Figure 26a, NWS - Minneapolis; Figure 26b, NWS - Marquette) . This event was made possible by a strong influx of moist air and temperatures cold enough to preserve heavy snow all the way to the ground.
A final large low pressure center formed as the mid-tropospheric trough above reached its maximum amplitude, steering the jet stream down to Texas before returning northward. The surface low developed on the 28th along the northwestern coast of the Gulf of Mexico, and then proceeded northeastward, carrying enormous amounts of moisture into the south central and eastern Midwest. Rain exceeded 5 inches over much of western Kentucky, with 11.38 inches measured in Murray, KY, during the several days of rain (including rain from the previous low pressure system). Serious flash flooding and stream flooding resulted in warnings being issued in at least 20 Kentucky counties. The Ohio River at Smithland, KY, rose from less than 15 feet to a stage greater than 35 feet by the beginning of December (Figure 27, USGS). Fortunately, damage was isolated, and only one potentially flood-related death was identified in Kentucky.