A significant severe weather and tornado outbreak affected the Southern United States between December 16–17, 2019. Discrete supercells developed in the early morning on December 16 and moved northeast, spawning multiple strong, long-tracked tornadoes in cities such as Alexandria and in Laurel before congealing into an eastward-moving squall line. During the outbreak, the National Weather Service issued several PDS tornado warnings as well as a rare tornado emergency for Alexandria. In addition to this, the Storm Prediction Center issued six tornado watches for the outbreak. The event happened to take place on the same date of another outbreak in a similar area 19 years earlier. It also occurred in a similar area later impacted by the December 28–29, 2024 tornado outbreak.
Meteorological synopsis
The first signs of organized severe weather came on December 12, when the Storm Prediction Center (SPC) outlined a day 5 risk area across portions of the Mid-South and lower Ohio River Valley. This 15% delineation area was shifted southwestward the following day and translated to a broad Slight risk for severe weather on December 14. In their first day 2 outlook, the SPC introduced an Enhanced risk across portions of Louisiana, Mississippi, and Alabama. By the late morning of December 16, a Moderate risk area was introduced from eastern Louisiana through central Mississippi.
Expectations of a tornado outbreak arose on December 16 as a well-defined, positively tilted trough existed across the central United States and very strong cyclonic flow developed southeast of this feature. At the surface, a cold front was expected to progress across the Southeast United States while an intensifying area of low pressure propagated northeast along the boundary. The environment along and ahead of this front was anticipated to be favorable for severe weather, featuring dewpoints as high as the low 70s Fahrenheit, mid-level Convective Available Potential Energy on the order of 1,000–2,000 J/kg, and a contributing to large hodographs and strong cyclonic updraft potential. In addition, advection of drier air aloft was predicted to inhibit convective development until later in the day. Given the general alignment of the cold front and wind shear aloft, the SPC was uncertain early on December 16 over whether numerous discrete supercells would exist in the highest threat area. By later in the day, however, a consistent signal for sustained warm-sector supercells from available model guidance lent credibility to the potential for multiple significant tornadoes. At 16:40 UTC, the SPC issued their first tornado watch, the first of four during the day as the severe weather threat spread eastward. Discrete supercells soon developed within the warm sector across Louisiana, while a line of thunderstorms congealed along the encroaching cold front. Numerous tornadoes, some strong to intense, were observed across Louisiana and Mississippi throughout the afternoon hours. By late evening, isolated supercells were overtaken by the squall line, reducing the significant tornado threat. The following morning, the storms propagated eastward into Georgia, where a few additional tornadoes occurred before the outbreak came to an end.
Confirmed tornadoes
December 16 event