Midwest Overview - December 2015

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Warmest December on Record for the Midwest

December 2015 was unseasonably warm across the Midwest and ranked as the warmest December on record. All nine Midwest states also experienced their warmest December on record (1895-2015). All areas across the Midwest were at least 6°F above normal, with some portions of Wisconsin, eastern Ohio, and eastern Kentucky up to 12°F above normal (Figure 1). The preliminary region wide December temperature was 36.7°F, which was 10.7°F above normal and broke the previous record set in 1923 by 2.6°F. The state with the greatest departure from normal was Wisconsin, where the preliminary statewide temperature of 31.7°F was 12.3°F above normal and 3.6°F above the previous December record set in 1923. Details about the record-breaking warmth in the other eight states are listed in the table below.

	December 2015 Temperature (Rank)	Difference from 1981-2010 Normal	Previous Record (Year)
Illinois	41°F (1)	+11.1°F	38.9°F (1923)
Indiana	42.4°F (1)	+11.5°F	39.9°F (1982)
Iowa	32.9°F (1)	+9.9°F	32.2°F (1931)
Kentucky	48.5°F (1)	+11.9°F	45.1°F (1923)
Michigan	35.5°F (1)	+10.6°F	31.9°F (2001)
Minnesota	24.9°F (1)	+10.4°F	24.1°F (1939)
Missouri	42.1°F (1)	+9°F	41.6°F (1931)
Ohio	43.4°F (1)	+11.9°F	39.4°F (1982)
Wisconsin	31.7°F (1)	+12.3°F	28.1°F (1923)
MIDWEST	36.7°F (1)	+10.7°F	34.1°F (1923)

Several record daily high temperatures were broken throughout the month. A slew of records were broken across the region between December 12-14, with some locations recording 70°F or higher during this time (Figure 2) (Figure 3) (Figure 4). The end of the month also saw significantly above normal temperatures, with the majority of Kentucky and southeast Ohio recording temperatures between 65°F to 77°F on December 27 (Figure 5).

Wettest December on Record for the Midwest

Not only was it the warmest December on record for the region, but it was also the wettest December. Monthly precipitation totals ranged from 0.5" in northwest Minnesota to 10" to 12.5" across portions of Missouri (Figure 6). With the exception of northwest Minnesota, monthly totals were above normal for the region (Figure 7). Precipitation was twice the normal amount across much of Illinois, Wisconsin, Iowa, and Missouri with some locations in Iowa receiving four to five times the normal December precipitation.

The preliminary region wide December precipitation was 5.01", which was 2.8" above normal and well above the previous record of 4.42" set in 1982. For individual states, Iowa and Wisconsin experienced their wettest December on record. Illinois, Missouri, and Minnesota experienced their second wettest December on record, while all other Midwest states ranked among the top eight wettest (details below).

	December 2015 Precipitation (Rank)	Difference from 1981-2010 Normal	Previous Record (Year)
Illinois	6.64" (2)	+3.95"	7.17" (1982)
Indiana	5.55" (5)	+2.42"	7.02" (1990)
Iowa	5.01" (1)	+3.72"	3.4" (1982)
Kentucky	6.68" (8)	+2.38"	10.67" (1990)
Michigan	3.89" (3)	+1.73"	4.23" (2008)
Minnesota	2.04" (2)	+1.15"	2.06" (1968)
Missouri	7.86" (2)	+5.13"	7.99" (1982)
Ohio	4.28" (8)	+1.35"	7.53" (1990)
Wisconsin	4.47" (1)	+3.07"	2.98" (1968)
MIDWEST	5.01" (1)	+2.8"	4.42" (1982)

After a wet December, drought concerns remain minimal across the Midwest (Figure 8). At the beginning of December, only 3.16% of the region was in drought and by the end of the month, this reduced to 2.35%. The main area of improvement was in the Upper Peninsula of Michigan. On the other hand, a small portion of northeast Ohio is now considered to be in moderate drought. Other drought areas that did not see much improvement in December were portions of central Indiana, northern Indiana, and southern Michigan.

December Snowfall was Below Normal across Majority of Midwest

The well-above-normal precipitation resulted mainly from rainfall and not snowfall, since snowfall across much of the region was below normal for December (Figure 9). Snowfall in portions of Upper Michigan was as much as 20" to 40" below normal. On the other hand, southwest Minnesota, northwest Minnesota, and northwest Iowa received snowfall that was 5" to 15" above normal. Monthly snowfall totals ranged from 0.1" across much of the central and southern portions of the Midwest to 20" to 25" in southwest Minnesota (Figure 10). There were two events that produced the majority of snowfall throughout the month - one at the very beginning of the month November 30-December 2 and the other at the end December 28-29.

Flooding, Severe Weather, and Other Significant Impacts

The wet conditions resulted in flooding across the region at times throughout the month. A strong storm system brought abnormally high precipitation to the region on December 12-14(Figure 11), which resulted in flood advisories and warnings across Iowa, Wisconsin, and Illinois. In Iowa, a statewide precipitation average of 2.8" of rain fall during this event. Only three winter months (Dec. 1982, Feb. 1881, and Feb. 1915) have brought more precipitation to Iowa than this one storm system. Minor to moderate flooding was recorded by river gauges across these states as well.

On December 23, a storm system caused heavy rain, strong winds, and tornadoes across Illinois, Indiana, Kentucky, and southeast Missouri (Figure 12). The strongest tornadoes were EF-1 tornadoes in Chilton, MO; Pickneyville, IL; and Falmouth, KY. Winds reaching 90-100 mph were reported in Black Gnat, KY, which caused damage to barns in the region. Fortunately, no fatalities were reported from these storms.

The most notable event of the month occurred from December 26-29. This storm system brought heavy snowfall to Iowa, Minnesota, Wisconsin, and northern Michigan (Figure 13) while at the same time, torrential rainfall to areas further south in Missouri, Illinois, and western Kentucky (Figure 14). The torrential rainfall brought moderate to major flooding to parts of Illinois and Missouri, and moderate flooding to parts of Kentucky and Indiana. Some of the worst flooding occurred in Missouri, where local rainfall amounts for the 3-day period reached 9" to 11" in St. Louis and St. Charles counties in Missouri. Flash flooding was widespread in Missouri, resulting in hundreds of water rescues and major transportation impacts as portions of major interstates were closed for a period of time. Unfortunately, the historic flood claimed the lives of at least fifteen people in Missouri and nine in Illinois.

2015 Year in Review

Temperatures fluctuated from below-normal to above-normal throughout the year, resulting in average annual temperatures that were near- to slightly above-normal across a majority of the region (Figure 15). Below-normal temperatures were prevalent throughout the winter and summer, while the spring and fall seasons tended to run warmer-than-normal. The average annual temperature was above normal by 1°F to 3°F across much of Minnesota. The region wide annual temperature is 49.6°F, which is 0.9°F above normal.

2015 was the 2nd wettest year on record for the Midwest, with a region-wide precipitation total of 42.59" (the record is 42.73" set in 1993). Across the region, annual precipitation totals ranged from only 10" in northwest Minnesota to 60" to 70" in southern Missouri and southern Kentucky (Figure 16). A majority of the region received above-normal annual precipitation, with the exception of northwestern Minnesota where areas received as little as three-quarters of normal annual precipitation (Figure 17). The wettest months of the year were May, June, and December.

-MW-
Extension Climate Specialist for Illinois-Indiana Sea Grant and the MRCC.

The Iowa Climatology Bureau also contributed to this report.
The Missouri Climate Center also contributed to this report.