Will 2024 Go Out With a Bang? Severe Weather Outbreak Possible for Southeast Saturday and Sunday

*Update 12/28: On Saturday, The SPC has upgraded parts of the risk area to a MODERATE Risk and has introduced a 15% hatched strong tornado risk. This post has been updated accordingly* 

TLDR (Updated):

        It looks Mother Nature isn't ready to let the ball drop just yet as a potential severe weather outbreak looks possible for Saturday and Sunday. The Storm Prediction Center (SPC) has issued an MODERATE Risk (Level 4/5) for severe weather on Saturday (12/28) across Louisiana and the lower Mississippi Valley for damaging winds, large hail, and tornadoes (a few strong). Timing of the greatest threats looks to be during the afternoon and evening hours. For Sunday, we turn our attention to Georgia, the Carolinas, and Virginia where a SLIGHT and MARGINAL Risk has been issued by the SPC with the primary concern being damaging wind gusts. 

The SPC Day 1 Categorical Outlook. On Saturday morning, the SPC upgraded the area from Louisiana and the mid-lower Mississippi Valley into a MODERATE Risk category, which is a level 4/5. This risk level indicates the potential for widespread and potentially intense/long lived severe weather across the region 

Saturday 12/28 (Updated): 

A potent mid-level shortwave trough is expected to eject from the southern plains, triggering the development of a surface low. In response, a strengthening low-level jet combined with a lifting east-west oriented warm front will advect a warm, moist airmass characterized by mid to upper 60s dewpoints into eastern Texas and the Mississippi Valley. The strengthening wind field, cooling temperatures aloft, atop a warm and moist airmass will promote the potential for a severe weather outbreak capable of all hazards. 

The HRRR Modeled 500 MB (Mid-Level) Winds During Saturday Evening. This shows the strong, mid-level trough (dip or wave in the mid-level winds) ejecting from the southern plains, providing strong winds aloft and creating the development of a surface low. 

Saturday's event is expected to bring a mix of storm modes, including the potential for both supercells, semi-discrete supercells, and linear bowing segments. As such, all hazards appear possible with the tornado threat ramping up by the late afternoon and evening hours. With such a dynamic wind field with plenty of directional change atop a moderately unstable airmass, the potential is there for a few strong tornadoes (EF2+). 

A Modeled Skew-T or "Sounding" of the Atmosphere of The Lower Mississippi Valley for Sunday Afternoon/Evening. This sounding shows a robust environment for severe weather potential, including a warm and saturated airmass (red and green lines), sufficient buoyancy and potential for the airmass to rise (CAPE or MLCAPE),  a strong, curved hodograph showing a dynamic wind field (top right graph), and sufficient lapse rates (lower left corner). This sounding should not be taken literally but is an example of the atmospheric conditions that may lead to the severe weather potential 

*Saturday Strong Tornado Potential Update*

On Saturday morning, the SPC upgraded portions of Louisiana and Mississippi from a 10% tornado risk to a 15% risk. In addition, the SPC has maintained the "hatched" area, indicating the potential for strong to intense tornadoes (EF2+). Subsequently, the tornado risk has increased and there is a higher likelihood for a few strong to intense tornadoes than indicated yesterday.   

SPC Day 1 Tornado Outlook. This shows the forecasted probability of a tornado occurring within 25 miles of a point. On Saturday morning, the SPC upgraded the tornado risk across Louisiana and Mississippi into a higher 15% tornado risk. The SPC also included a "hatched" area, which indicates a 10% or greater for strong tornadoes (EF2+) 

Boom or Bust Potential?

There are a few things, however, that could limit the severe weather potential. A few early morning shows and storm were ongoing in the risk area prior to the event, which could limit destabilization and dampen the instability of the atmosphere. In addition, weaker low-level lapse rates (temperature change with height) could also dampen the "willingness" for the airmass to rise. Other potential issues include timing issues with the low-level jet strengthening and the mid-level trough ejection as well as too much congestion or "clustering" of storms. 

Sunday 12/29 (Updated):

For Sunday, our attention turns to the eastern seaboard, mainly Georgia, the Carolinas, and parts of the Mid-Atlantic (including Virginia). As this system pushes east, there might be enough instability to maintain a severe weather threat across the eastern seaboard. This primary threat will be damaging wind potential along a line of storms ahead of the incoming cold front, though a tornado or two is not out of the question. Timing of the threat is still getting fine tuned but expect the threat to be highest for us here in Central VA anytime between 3 PM through 11 PM 

SPC Day 2 Categorical Outlook. No changes were made regarding the risk level from Friday evening, however, the SLIGHT Rick area has been expanded somewhat further into Western and Central VA.