Midwest Weekly Highlights - December 11-17, 2006

Winter Takes a Holiday

The temperature moderation that began near the end of the first ten days of the month continued full throttle into this week. Temperatures ranged from 18°F above normal in northwestern Minnesota to "only" 6°F above normal over southeastern Kentucky (Figure 1). The largest departures (+15°F to +18°F) were found from south-central Missouri northward to the Canadian border. The much warmer weather made quick work of the snowfall from the December 1 storm, and by December 13 the snow was gone except for a few patches in north-central Illinois (Figure 2, NOHRSC). Runoff from the snowmelt produced minor flooding along the lower Illinois River during the entire period, and the river was expected to remain at or above flood stage into the third week of December.

Precipitation this week was near to above normal from north-central Iowa into the Michigan UP, and from southeastern Missouri northeastward into southern lower Michigan (Figure 3). In between these two bands, precipitation ranged from next to nothing in southwestern Missouri to 25 percent of normal in western Minnesota and eastern Ohio. Snowfall this week was limited to northern Minnesota, Wisconsin, and the Michigan UP (Figure 4), and the few inches of snow that fell was well below normal for this time of December. Extreme drought still holds fast over northern Minnesota and Wisconsin, and an area of Moderate drought exists over a small part of southwestern Missouri (Figure 5).

Showers and Thunderstorms

Most of the rain that fell in the Midwest this week was associated with one frontal system that moved through the region at the beginning of the period. The front entered the Midwest on December 11 and pushed through the region on December 12 and 13 (Figure 6). During the afternoon of December 12 a line of showers thunderstorms developed over Illinois and moved eastward, at one point extending from southern Lake Michigan to south of the Ohio River. Some small hail occurred with some of the storms during the late afternoon. One-half inch or more of rain fell from Indiana into southern lower Michigan, with some locations receiving almost two inches over a two-day period. The heavy rain caused some minor flooding along the Little Wabash River in southeastern Illinois and southwestern Indiana.

The week ended with the passage of another cold front on December 17. This produced light showers from eastern Illinois through the northern half of Indiana and Ohio, and brought only slightly cooler weather.

SDH