December’s Deadly Tornado Outbreak

 

December 10, 2021 Storm Reports  (Source: NOAA)

Severe weather in December is rare in the United States.  Severe weather refers to a thunderstorm that contains any of the following; wind gusts of at least 58 mph; hail 1”/+ in diameter; or a tornado.  The month of December averages the fewest number of tornadoes of any month with 24 according to NOAA’s National Center for Environmental Information.

A devastating severe weather outbreak occurred on December 10, with dozens of confirmed tornadoes.  The majority of them occurred late in the evening and overnight when a lot of people didn’t get the warnings in time to take appropriate safety precautions.  However, the watches and warnings were in place since it was a well forecast severe weather event by NOAA’s Storm Prediction Center.  Due to the powerful nature of many of the tornadoes, there have been dozens of reported fatalities.  By the time the final number of casualties is known, this could finish as the deadliest December tornado outbreak on record for the United States.

Tornadoes were reported from Arkansas to Ohio, with a few particularly intense EF-3 or stronger tornadoes.  NOAA crews have been busy surveying the damage and rescue teams have been searching for survivors.  Given the scope of the outbreak the final tornado count and intensity of the tornadoes may not be known for some time.  Meanwhile, it’s likely that the destructive tornado that occurred in Mayfield, Kentucky reached EF-5 intensity.

Although not an EF-5 intensity for its entire duration, the Mayfield tornado had a long track across four states and was dubbed the “Quad State Tornado” with a track of more than 200 miles.  Subject to final verification from NOAA, this could break the existing record for longest lasting tornado on record.  Tornadoes are ranked on the Enhanced Fujita Scale, with weak tornadoes being an EF-0 and the highest ranking an EF-5 with winds of greater than 200 mph. 

Several factors contributed to this tornado outbreak.  There was record warmth in the southern Plains states and Tennessee Valley.  Memphis, Tennessee, for example, had a record high of 79° this past Friday.  A powerful area of low pressure also helped create the “lift” in the unstable atmosphere that allowed for the intense, supercell thunderstorms to develop.  A “supercell” thunderstorm is large, long-lasting thunderstorm that rotates.

If the Mayfield tornado is confirmed as an EF-5, it will the first since May 20, 2013 in Moore, Oklahoma.  That would end the longest stretch in U.S. history no F5/EF-5 tornado has occurred.  It would also be the first December EF-5 tornado, and third overall, since December 18, 1957 when one was observed in Sunfield, Illinois.  Accurate tornado records date back to 1953.   Fortunately, as rescue operations continue, NOAA’s Storm Prediction Center doesn’t expect any severe weather in impacted areas during the next few days.