Midwest Overview - December 2006

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Not Your Typical December

Despite a cold and snowy start to the month, December 2006 ended as a very warm and wet month across much of the Midwest. Temperatures the first ten days of December were below normal across the entire region, ranging from only 2°F below normal in western Minnesota to 12°F to 14°F below normal from southwestern Missouri into central Illinois (Figure 1). The large below-normal departures in this region were due to a deep snow cover resulting from a storm which moved through the Midwest on November 30-December 1. Temperatures the last 21 days of the month ranged from 8°F above normal in southeastern Kentucky to 18°F above normal in northwestern Minnesota (Figure 2). The effect of the deep snow cover on temperatures was still evident on the map of temperature departures for the month, with a narrow band of departures of only 3°F to 6°F above normal from southwestern Missouri to southern Lake Michigan (Figure 3). Temperatures for December 2006 ranged from 9°F to 10°F above normal in Minnesota to 2°F to 3°F above normal across far southern portions of the Midwest. Preliminary data indicate that December 2006 is tied as the fifth warmest December in the 9-state Midwest region in the past 112 years (tied with 1965 and 1982). In Minnesota, were the largest temperature departures were observed, preliminary data ranks December 2006 as the third warmest on record.
 

Rain Falls in Ohio Valley

A southern storm track during December brought a series of low pressure systems through the southern Midwest, and this resulted in much above normal precipitation through the Ohio Valley (Figure 4). Most of the region received normal to much above normal precipitation with the exception of Kentucky and southeastern Ohio, where precipitation ranged from less than 50 to 75 percent of normal. Actual precipitation amounts ranged from more than 6 inches in southern Indiana to less than an inch in northern Minnesota (near normal for that region)(Figure 5). The series of heavy precipitation events in the southern half of the region caused a number of smaller rivers to reach or exceed flood stage in Illinois, Indiana, and western Ohio, resulting in minor flooding of mostly agricultural lowlands. Snow melt from from the storm at the beginning of the month, combined with above normal rainfall the remainder of December kept the Illinois River near or above flood stage at a number of locations through the end of the month.
 

Where's the Snow?

Snowfall was generally well below normal across the Midwest in December, with the exception of the areas in the path of the December 1 storm (Figure 6). Up to 12 to18 inches of snow lie on the ground from Missouri through north central Illinois into southeastern Wisconsin on December 1. Heavy snow also piled up on the western shores of Lake Michigan as lake-effect snow occurred behind the system (Figure 7). However, by December 13 only a few patches of snow remained as the unseasonably warm weather took hold. Snow the remainder of the month was largely limited to northern Minnesota and Wisconsin (Figure 8). At the end of December snow cover across the Midwest was well below normal, with the exception of a small part of central Wisconsin which received heavy snow from a storm just prior to Christmas (Figure 9).

SDH