Midwest Weekly Highlights - December 25-31, 2019

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Exceptional Warmth

Temperatures 10°F or more above normal were widespread across the Midwest during the final week of December (Figure 1).  Parts of Illinois, Indiana, Ohio and Kentucky were 12-15°F above normal, with some areas of northern Ohio more than 16°F above normal.  Temperatures in the 50s and 60s were common across the southern two-thirds of the region, with some areas reaching the 70s in Missouri and Kentucky on Christmas Day (Figure 2).  Minimum temperatures were even more above normal in eastern Minnesota and northern Wisconsin (Figure 3).  Values 16-19°F above normal were observed in these areas.  A combined more than 825 daily high maximum and minimum temperature records were broken across the region (Figure 4).
 

Extreme Precipitation

A week of extremes in the Midwest included very heavy precipitation across the region, especially in the Upper Midwest (Figure 5).  More than an inch of rain fell in most areas except central Iowa and northeastern Ohio.  Amounts over 1.5 inches were recorded across Kentucky, Michigan and northern Wisconsin.  In the Upper Midwest, these amounts translated to 4-5 times the normal amount (Figure 6).  Most of Iowa, northern Illinois, northern Indiana, western Missouri and Kentucky had 2-3 times the normal amount.  More than 400 daily precipitation records were broken during the period (Figure 7).  Heavy snow also impacted the Upper Midwest (Figure 8).  Areas in northwestern Minnesota had more than five times the normal amount as a system stalled over the region (Figure 9).
 

December 28-31 Winter Storm

A slow-moving winter storm stalled in the eastern High Plains and led to heavy snowfall and precipitation across the region.  Rain began across most of the region on December 28 through the morning of December 29 (Figure 10), while temperatures remained above freezing except in northwestern Minnesota.  Amounts of over 0.75 inches were common across Missouri, Illinois, Iowa, Wisconsin and eastern Minnesota.  Meanwhile, snowfall amounts of 4-6 inches were common in northern Minnesota, with locally heavier amounts over 8 inches (Figure 11).  Heavy rainfall moved east across the Ohio River Valley on December 29 through the morning of December 30 (Figure 12).  Amounts over 1.5 inches were widespread in Kentucky, while most of Indiana, Ohio and Lower Michigan had more than 0.75 inches.  Heavy snow was once again recorded across northwestern Minnesota, northern Wisconsin and the U.P. of Michigan (Figure 13).  While heavy precipitation subsided in the southern Midwest (Figure 14), colder temperatures and a second burst of energy led to heavy snow from eastern Minnesota through Michigan on December 30 through the morning of December 31 (Figure 15).  Snowfall amounts of 3-5 inches were common, with lake-effect snowfall amounts over 8 inches in the U.P. of Michigan. The heavy snowfall from this event led to more than 60 daily snowfall records across the Upper Midwest (Figure 16).
 

-BJP-