Above Normal Temperatures Continue

Above normal temperatures continued through the second week of December throughout most of the Midwest, except for parts of northern Wisconsin and Michigan’s Upper Peninsula (Figure 1). Large portions of Illinois, Iowa, and Missouri exceeded 8°F above normal for the week. Lincoln County, located in eastern Missouri, reported an average temperature of 46.5°F. This was 12.5°F above normal. Northern Minnesota’s average temperature ranged from 3°F to nearly 9°F above normal. In Koochiching County, Minnesota (north), average maximum temperature was 21.9°F (8.5°F above normal). Average temperatures were near normal to over 5°F below normal in Wisconsin. Rusk County, located in north central Wisconsin, recorded an average temperature of 16°F, which was 5.2°F below normal for the week. Both average maximum and minimum temperatures were above normal for most of the Midwest, but the most extreme departures were observed in maximum temperatures (Figure 2). The largest departures occurred from Missouri extending into the Ohio River Valley where average maximum temperatures ranged from 5°F to almost 17°F above normal.

Near Normal to Above Normal Precipitation Recorded

Frontal systems coupled with precipitation resulted in normal to above normal precipitation across the region for the week (Figure 3). Southern Minnesota, northern Iowa, Wisconsin, Illinois, Indiana, Michigan, Ohio, and Kentucky recorded 0.5 inches to 2 inches above normal. Heaviest precipitation amounts occurred within more intense storms. Widespread precipitation amounts ranged from 0.01 to 1 inch. Isolated areas in northern Illinois extending into Indiana, southern Indiana into Ohio, and Kentucky received more than 1 inch of precipitation (Figure 4). Most of the heaviest precipitation bands followed storm tracks that occurred on December 10th. Bowling Green, in western Kentucky, measured 3.08” of precipitation. This was 1.84” above normal for the week. Northwest Missouri into southwest Iowa, and north central Minnesota, missed out on any precipitation.

Complex Storm System Wreaks Havoc on Midwest

A strong low-pressure system impacted much of the Midwest December 10th into December 11th delivering snow to southwestern Minnesota, Wisconsin, and northern Michigan and severe storms to Missouri, Illinois, Indiana, Kentucky, and Ohio (Figure 5 from NWS Twin Cities). This storm system resulted in 81 fatalities and over 100 injuries in the Midwest alone, and initial estimates of up $4 billion in total damage.

Dew Point Temperatures - Surging moisture from the Gulf of Mexico allowed for maximum dew point temperatures to exceed 50°F in many locations across the central and lower Midwest, which is rare for December. Davies County Airport, in southwest Indiana, recorded a maximum dew point of 65°F (Figure 6). Since 2014, this station has only recorded December maximum dew point temperatures greater than 60°F on eleven days.

Tornadoes – There were 61 tornadoes across the 9-state Midwest region on December 10-11. Mayfield and Dawson Springs, located near Bowling Green in western Kentucky, were victims of the most devastating tornadoes. The NWS Paducah, Kentucky office did an extensive analysis of the tornadoes through this area. NWS storm surveys concluded an EF-4 tornado began in northwest Tennessee and traveled through western Kentucky. The total path length was 165.7 miles, estimated peak winds of 190 mph, maximum width of greater than a mile, and greater than 55 deaths in the NWS Paducah area. An additional EF-3 tornado traveled 122.7 miles through northwest Tennessee into western Kentucky. The estimated peak winds were 160 mph and an estimated maximum width of 1038 yards. There were 13 deaths associated with this tornado. Full analysis of additional tornadoes can be found here. There were 5 additional EF-3, 9 EF-2, 9 EF-1, and 3 EF-0 tornadoes in the Midwest region.

Winds – Windy conditions were widespread with much of the Midwest recording average wind speeds in excess of 16-25 mph on December 11 (Figure 7). Widespread sustained, maximum wind speeds ranged from 21-45 mph (Figure 8), with higher gusts. In Kentucky, two mesonet stations are being investigated for having potentially measured a record setting wind gust on December 10th (Graves County, 107.1 mph; Caldwell County, 120.1 mph). Jasper County Airport, located in northwest Indiana, clocked in a maximum wind speed of 40 mph. NWS Detroit reported a high wind gust at the Detroit Wayne Airport of 64 mph. Tazewell and Macon Counties, located in central Illinois recorded 85 and 80 mph wind speeds. There were reports of significant structural damage, trees uprooted, widespread power outages, and unharvested corn fields being flattened as a result of the storm winds across the region. In total, 234 severe wind reports were recorded across the region from December 10-11.

Hail – There were 6 hail reports across the Midwest. Two storm spotters reported quarter sized hail near Marthasville and Ballwin Missouri (both western suburbs of St. Louis).

Snow - Total snowfall for the week was heavily influenced by this storm system. Through December 10-11, snowfall totals ranged from 1 to 15 inches, with the largest accumulations in southern Minnesota northeastward into the Upper Peninsula of Michigan (Figure 9). By the end of the week, widespread snowfall totals were 1-15", with isolated spots receiving up to two feet of snow (Figure 10). Along the central axis of the snowfall, totals ranged 175 percent to over 750 percent of normal for the week (Figure 11).

Drought Lingers

There were slight expansions and intensifications of abnormally dry and drought conditions in the Midwest this week (Figure 12). A westward expansion of the D0 (Abnormally Dry) was observed in western Missouri. Intensification of D1 (Moderate Drought) to D2 (Severe Drought) in central Wisconsin was reported. Total percent land area in the region in D1-D4 (Moderate, Severe, Extreme, and Exceptional) was 17.97%, a 0.53% increase from the previous week. It is important to note that 0% of the land reported D4 (Exceptional Drought). Indiana, Ohio, and Kentucky continued to not report any abnormally dry or drought conditions given adequate rainfall amounts.