Severe Weather: A Rarity in December

 

December 2021 Severe Weather  (Source: NOAA)

Severe weather in December is relatively rare in the United States.  The month of December averages the fewest number of tornadoes of any month with 24, according to NOAA’s National Center for Environmental Information.  Despite this fact, there have been several deadly December severe weather outbreaks in recent years.  “Severe weather” is defined as a thunderstorm that contains any of the following: wind gusts of at least 58 mph, hail 1”/+ in diameter, or a tornado.

2021: A year has passed since December’s deadliest tornado outbreak on record in the United States.  A total of 66 tornadoes touched down on December 10-11, 2021, from Arkansas to Ohio.  This was an especially deadly outbreak since most of the tornadoes occurred at night, including an EF-4 tornado that devastated the town of Dawson Springs, Kentucky.  The state of Kentucky had 80 tornado-related fatalities.  According to NOAA, there were two EF-4 tornadoes and another six EF-3 tornadoes.  Tornado intensity is ranked on the Enhanced Fujita Scale from minimal EF-0 tornadoes with winds of up to 85 mph to an EF-5 with winds over 200 mph.

Several factors contributed to this tornado outbreak.  There was record warmth in the southern Plains states and Tennessee Valley.  That was followed by a powerful area of low pressure which helped create the "lift" in the unstable atmosphere that allowed for the intense, supercell thunderstorms to develop.  A "supercell" thunderstorm is a large, long-lasting thunderstorm that rotates.  A "derecho" brought another 513 severe weather reports across the Upper Midwest on December 15.

2020: A two-day severe weather outbreak on December 23-24 covered a large geographic area with confirmed tornadoes from southeastern Texas to southern Virginia.  Aside from the unusually wide area impacted by this outbreak, several of the tornadoes were quite damaging.  It’s also unusual for the state of Virginia to see tornadic thunderstorms in December.  Fortunately, no fatalities were reported.

2019: Another severe weather outbreak that spanned two days, December 16-17, saw confirmed tornadoes from Louisiana to Georgia.  A total of three fatalities were reported along with several injuries.  Hail 1” – 2” in diameter was also reported in several locations across the Deep South on December 16.    

2018: Over three dozen tornadoes developed and caused extensive damage across the state of Illinois on December 1.  According to the U.S. Storm Prediction Center, the strongest tornado was an EF-3 tornado with winds of 155 mph in Christian County, IL.  Fortunately, there weren’t any reported fatalities during this rare December tornado outbreak.  Based on NOAA data, this was the largest December tornado outbreak in Illinois state history.