Temperature and Precipitation Anomalies.

The Midwest was on course to experience record warmth for a second month in a row when the highly above normal temperatures of the first 21 days of December finally gave way to a blast of colder than normal conditions in the last 10 days of the month. Despite the cold ending to the month, the Midwest still had its 6th warmest December on record, Michigan its 2nd warmest, Minnesota and Wisconsin their 7th warmest, Ohio its 8th warmest, and Iowa and Kentucky their 9th warmest. Temperatures were 7-9°F above normal in the northern Midwest, and 3-5°F above normal in the southern Midwest (Figure 1).

A persistent storm track through the Ohio Valley during the warm part of the month combined with heavy lake effect snows at the end of the month to allow the Midwest to register its 36th wettest December, despite widespread dryness in the western Midwest and many fair days throughout (Figure 2). The lower Ohio Valley received up to 200% of the normal December precipitation, resulting in some river flooding in southern Indiana especially (Figure 3). The arrival of the cold air above warm and ice free Great Lakes waters spawned very heavy lake-effect snowfall along the southern shores of Lake Superior and Lake Erie, and the eastern shore of Lake Michigan, including several record daily snowfall totals in Grand Rapids and Marquette. Besides the usual lake effect belts, though, the snowfall for the month was considerably less than normal away from the lakes (Figure 4).

Extreme Events and Impacts.

December 5th was a very unusual day for the Midwest. A strong cold front was at the peak of its energy in the afternoon, forming a squall line hundreds of miles long across Iowa and adjacent states (Figure 22, NWS). There were even some severe hail and wind reports noted that caused damage to structures in Iowa (Figure 23, Storm Prediction Center). Ahead of the front, a strong southerly wind brought record warmth to cities throughout the region, including: Chicago, Rockford, and Peoria, IL; Lamoni, Mason City, Ottumwa, Waterloo, Dubuque, Moline, and Burlington, IA; Indianapolis, South Bend, Evansville, and Fort Wayne, IN; Cleveland, Akron, Mansfield, Columbus, Dayton, Toledo, and Youngstown, OH; Detroit, Sault Ste. Marie, Alpena, Houghton Lake, Traverse City, Marquette, Grand Rapids, Lansing, and Muskegon, MI; Minneapolis and Eau Claire, MN; Wausau, Oshkosh, Appleton, Green Bay, Madison, and Milwaukee, WI; Kansas City, St. Louis, and St. Joseph, MO; and Lexington, Louisville, and Bowling Green, KY. This day was extraordinary in terms of the overall temperature field, which looked like a day in early September rather than early December (Figure 24, the number of first order stations reporting records (more than 40), and the extent to which some of the previous maximum temperature records were shattered (by 5 to 9°F in a number of cases). The excessive warmth did have some negative impacts. Fruit trees and ornamental plants prematurely activated, cold weather recreation was shut down, and agricultural pests become more likely to winter-over. However, the positive economic impact of low heating costs was likely to be of tremendous benefit to all, and the transportation safety and human health impacts of a typical winter were reduced considerably.

The most significant weather event later in the month occurred on December 16-18, when a low pressure area from Texas moved into southern Missouri, then slowly transited up the Ohio Valley through the Midwest. Heavy rain amounting to 2-4 inches fell near the meeting place of Missouri, Illinois, Kentucky, and Indiana (Figure 25 and Figure 26, NWS). This area suffered from both flash flooding and substantial river flooding. The East Fork of the White River near Bedford, IN, reached more than 10 feet above flood stage (Figure 27, USGS), while the Big Muddy River in Murphysboro, IL, was more than 12 feet above flood stage (Figure 28, USGS). A woman driving a car in southeastern Indiana entered a flooded road, and was drowned after exiting her car in the rushing water; fortunately, rescue workers were able to save her two children still in the car. Rescuers also saved a couple that was swept away nearby in a similar incident, though they suffered severe hypothermia.