Overall, Below-Normal Temperatures; Unseasonable Warm and Cold

Looking at the last week of December, temperatures were below normal throughout the entire Midwest, excluding Michigan where temperatures were at or above normal (Figure 1). Iowa’s mean temperature was 13.9°F (7.1°F below normal), making that the largest statewide temperature departure. Vernon County, Wisconsin, was 12.2°F below normal earning the title of the largest temperature departure in the Midwest. Below-normal max temperatures were widespread, with scattered pockets of near-normal temperatures in Michigan (Figure 2). Minimum temperatures were also below normal everywhere, except Michigan. Temperatures reached 11°F below normal in southeastern Kentucky (Figure 3). Despite an overall pattern of below-normal temperatures, the Midwest experienced a rollercoaster of temperatures this week. To start the week (12/22-12/26), most of the Midwest recorded mean temperatures up to 15°F below normal (Figure 4). As a result of this, 83 low minimum records were broken or tied and 215 low maximum records were broken or tied (Figure 5). On the other hand, a warm up occurred 12/27-12/31 leading to temperatures that were at least when 7°F above normal across the Midwest (Figure 6). There were 195 high maximum and 206 high minimum records broken or tied this week (Figure 7). This table from NWS Chicago shows historic 6-day warmups in Chicago and Rockford; from this event, Chicago warmed up to 67°F and Rockford warmed up 71°F.

Below-Normal Precipitation Pattern

This week, precipitation was generally below normal, besides scattered areas in Minnesota, Wisconsin, Michigan, Indiana, and Ohio that received 150-400 percent of normal precipitation (Figure 8). Michigan’s Upper Peninsula received the most precipitation this week, where Chippewa County received the highest total (4.05 inches). Dodge County, Wisconsin, recorded the highest one-day maximum of 2.25 inches on December 22. This week, 52 precipitation records were set (Figure 9). Streamflow conditions in the Central Midwest moved closer to normal conditions, but worsened in Missouri and the Ohio River Valley (Figure 10).

Pockets of Above-Normal Snowfall

Scattered parts of the region received 200 percent or more of normal snowfall and the Ohio River Valley saw up to 750 percent of normal snowfall (Figure 11). Michigan’s Upper Peninsula received totals upwards of 50 inches of snow (Figure 12). The highest total recorded this week was 49.3 inches in Chippewa County, Michigan, and the highest one-day maximum was 26.5 inches of snowfall on December 24 in Antrim County, Michigan. This week, 123 snowfall records were broken or tied (Figure 13).

Winter Storm

An intense Arctic cold front traversed the central US December 22-25 blanketing the region with frigid temperatures, high winds, and snow. Air temperatures plunged sharply and rapidly, with one-day temperature changes of 20-40°F across the lower Midwest. NWS Green Bay highlights the widespread cold temperatures throughout the US in this map. Dangerous wind chills from -20 to -40°F gripped the Midwest as winds gusted 30-50 mph and higher. Chicago and Des Moines clocked over 80 consecutive hours with subzero wind chills. In northwest Minnesota, wind gusts approached hurricane strength with a 74 mph gust recorded in Grand Marais. While snowfall across the lower Midwest was a modest 1-5 inches, high winds caused extensive blowing and drifting that halted ground and air transportation for days. Whiteout conditions caused a 50-vehicle crash on the Ohio Turnpike on December 23 that killed four people. Ten additional weather-related fatalities across four Midwestern states have been reported by media. Localized power outages, broken water mains, and frozen pipes were reported across the region. Across the upper Midwest, snow totals ranged from 3-10 inches, with 20-30 inches in lake-effected areas of northern Michigan.