Breaking Down the Historic WABBLES Tornadoes

Pierce Larkin is an alumni of WKU’s Meteorology Program, and a former moderator of WxornotBG. He’s now a bonafide NWS Meteorologist, working & forecasting out of the Columbia, South Carolina office. We greatly appreciate his expertise in breaking down this significant event with a guest post. Thanks so much, Pierce!

The radar of the supercell as it was pushing through Bowling Green. h/t GRLevelX

During the early morning hours of December 11th, a prolific supercell moved out of western Tennessee and into southern Kentucky. This devastating storm had already produced one long very long track tornado before moving into our area. Then, it produced 4 tornadoes across WABBLES, including the devastating Bowling Green 165mph strong EF3. Just over a week removed from the event, and all of the surveying done, we’ll do a quick recap of the atmosphere behind this event.

The general set up featured a strengthening surface low that moved from southeastern Colorado on Friday morning to the Great Lakes by Saturday morning. The wind field with this system was quite impressive, and with a slowish moving cold front, a large area of warm, moist air developed across the OH and MS Valleys. By Midnight, Bowling Green’s surface observation revealed a startling number, especially in December – 70F temperature, with a 65F dewpoint.

The midnight surface analysis on December 11th. Bowling Green is well within the warm sector ahead of the cold front. This allowed favorable instability and wind shear to combine. h/t WPC

Given upstream sounding (a look at temp, moisture, pressure and wind in the atmosphere) observations at 6pm that evening, this suggested that the instability had been realized. Looking at a proximity sounding from a high resolution model that evening, the atmosphere was primed in a way not seen in the lower OH Valley in a long time. 1300 j/kg of MLCAPE (thunderstorm energy) combined with an immense amount of wind shear in the lower 1km of the atmosphere is a bad combination. This usually yields high end severe weather, and unfortunately, that occurred.

The HRRR proxy sounding ahead of the supercells. This level of instability is rarely realized during Spring afternoons, let alone December! The combination of this and the intense wind shear allowed strong tornadoes to develop. h/t SHARPpy

For some context, let’s look at the Nashville sounding climatology. That amount of MLCAPE would easily exceed the record for Dec 10th or 11th (previous record was 526 j/kg). 1300 j/kg is much more common in May and June, let alone December in the middle of the night! The shear profile is easily with in the 90th percentile for the time of year, and approaching max observed values. This was a unique environment primed for supercells and tornadoes.

This unique environment actually promoted a unique morphology of the storm itself. It grew out of a line of storms with embedded supercells, became a dominant supercell, and then became a prolific tornado producer within a line. This is unusual, and is a testament to how intense the environment was.

The evolution of the Bowling Green supercell. It produced 13 tornadoes by itself, spanning from western Tennessee to the heart of central Kentucky. Visualization via Pierce Larkin

Ultimately, the storm produced a strong EF3 tornado as it pushed through Bowling Green. The winds were estimated to have been around 165 mph, changing Warren County forever. There were actually two tornadoes near Bowling Green, with a weaker tornado developing south of the primary one and interacting with the stronger one. Once the storm pushed out of WABBLES, it went on to impact Boyle, Green, Hart, Marion, and Boyle counties in Kentucky. One EF3, three EF2s, and multiple EF1s in this area of the state.

The tornado tracks and details across the WABBLES area. Data from the NWS.

I’d like to thank Landon for letting me come back to do this quick recap. I dearly love the state of Kentucky, and Bowling Green. I grew up in Kentucky, met my wife & got engaged at WKU, learned my craft & met some of my best friends there. Even though I live and work in South Carolina now, I feel the pain of the tornadoes across the state. My prayers are with Bowling Green and the rest of the state as the long process of recovery begins. 💚BG