Temperatures across the region were incredibly warm over the period. Almost the entire region had average temperatures over 10°F above normal, while a majority of the region was more than 15°F above normal (Figure 1). Many areas were even warmer, with airports at cities such as Chicago, IL, Cedar Rapids, IA, Evansville, IN, and Green Bay, WI all having average temperatures more than 20°F above normal for the period. Maximum (Figure 2) and minimum (Figure 3) temperatures of 10-20°F above normal were also common.
Daily maximum temperatures felt more like October than December during an incredibly warm three-day period from December 12-14. Maximum temperatures were in the upper 60s across most of Kentucky and southern Missouri through the morning of December 12, with parts of the Upper Ohio River Valley in the lower 60s (Figure 4). By the next day, 60s were common across Illinois, Missouri, Indiana, Ohio and Kentucky, with parts of southeast Iowa and southern Michigan also in the 60s (Figure 5). Low 70s were common across southern Missouri, southern Illinois, Kentucky and southeastern Ohio. Maximum temperatures continued to stay in the 60s or warmer across the southern half of the region through the morning of December 14, with 50s common across most of northern Lower Michigan and the eastern U.P. (Figure 6).
Record daily high maximum temperatures were set at many stations across the region during this three-day period. Many of these maximum temperature records occurred at major Midwest cities. St. Louis, Detroit and Cincinnati broke records on December 12 (Figure 7). Green Bay, Milwaukee and Toledo set records on December 13 (Figure 8). Cleveland, Madison and the Quad Cities had records on December 14 (Figure 9). Many record high minimum temperatures were also set during the three-day period.
With the month of December near the half-way point, the Midwest experienced one of its warmest starts to winter. A majority of the region was over 10°F above normal, while most of Wisconsin and Minnesota were 15°F or more above normal (Figure 10). The probability of above normal temperatures remained high through the end of December
(Figure 11), increasing the chances that December 2015 may be one of the warmest Decembers on record for the Midwest.
Abnormally Wet Weather
A strong storm system brought abnormally high amounts of precipitation to the region (Figure 12). Over an inch of precipitation fell across areas of Missouri, Iowa, northern Illinois, southern Wisconsin and northwest Michigan on December 12-14. Higher amounts were found in central Iowa and in the Minnesota-Iowa-Wisconsin tristate area, where more than two inches of precipitation fell through the morning of December 14 alone (Figure 13). Daily precipitation records were set on December 13 in Des Moines (1.79 in.) and Moline, IL (1.23 in.), while Dubuque set its December record for one day precipitation at 2.08 inches.
Most of this precipitation came in the form of rain, which stressed creeks and rivers. Flood advisories and warnings were seen across Iowa as well as in Wisconsin and Illinois. Minor to moderate flooding was recorded in these areas (Figure 14). Many of these river gauges were forecast to quickly recede.
Most of Iowa had more than five times the normal amount of precipitation for the period, and more than the normal amount for the entire month of December (Figure 15). An estimated 2.88 inches of precipitation has fallen across Iowa so far in December 2015, which would already rank as the second wettest December on record for the state.
While most of the precipitation was concentrated from December 12-14, moderate amounts of snow also fell across northern Minnesota, northern Wisconsin and the U.P. of Michigan during the period
(Figure 16). Light snowfall also occurred in southwest Iowa. Snowfall remained below normal for the period in most of these areas (Figure 17).
Drought Improves in the U.P.
Wetter weather in the U.P. of Michigan eliminated drought in the latest Drought Monitor from the National Drought Mitigation Center (Figure 18). Abnormally dry conditions also improved across the peninsula. Minor drought improvements were also seen in Indiana. Less than two-and-a-half percent of the region was considered to still be in moderate drought.