An Active Start to 2024

2023 was an unusual year for severe weather across the Columbia, SC forecast area, with significant breaks in the action in our normal active season (Spring and early Summer). However, 2024 has rocketed off to a very fast start.

A remarkably well forecast and intense, large scale system developed across the eastern CONUS in the days leading up to January 9th. Ensemble guidance as early as a week in advance began to hint at a series of systems developing and impacting us during the second week of January. This was expected to culminate in a more significant system on January 9th across the eastern US.

Given the well-forecast nature of the system, the national and local centers all began to message the system days in advance. This was a multi-hazard system, with intense non-thunderstorm winds expected, along with a strong line of severe thunderstorms pushing through with the front. Ensembles were consistently signaling one of the most intense wind events we have seen locally in years, which added confidence to the system occurring.

The meteorology behind this system was fascinating as an intense upper level trough dug into the western US, taking on a negative tilt as it approached the eastern 1/3rd of the CONUS.

This overspread the OH and TN Valleys with intense upper level divergence, which caused rapid lift across a large area of the country. When divergence aloft develops, it creates a deficit in air where it overspreads. This causes winds at lower levels in the atmosphere to fill the void, lowering pressure more and causing stronger winds as a result.

This is certainly reflected when looking at mid-level and low-level heights and winds, where we had 500 mb winds over 100 mph and 850 mb winds over 90 mph. This created an extremely favorable wind shear environment across the area, fostering a potential line of strong to severe storms. Additionally, an intense low-pressure system developed in the Mid-Mississippi Valley and pushed into the Great Lakes Region by the overnight hours. A secondary low developed along the lee side of the Appalachians through the day. The combination of rapid surface pressure falls across our area led to intense non-thunderstorm wind gusts that approached 60 mph.

The big question with this event was not whether or not we would have non-thunderstorm wind gusts. It was really whether we would get just enough instability to foster severe thunderstorms. There was significant forcing for lift from the large scale system, which likely offset the need for significant CAPE. The uncertainty didn't preclude the SPC from having an excellent forecast several days in advance.

As the day approached, hi-res guidance showed increasing chances that we would destabilize enough to support severe convection given the wind fields and lift along the front. The intense wind fields allowed moisture to advect into the region, creating enough destabilization to yield strong wind gusts and isolated tornadoes within the squall line. The line pushed through the area beginning late morning and cleared the eastern part of the forecast area by mid-afternoon. This produced widespread wind damage across the area, in addition to two tornadoes.

This event was impactful and interesting from a meteorological perspective. For starters, we had multiple tornadoes produced by this line, in addition to strong wind gusts with the line. More unusual than that is the constant wind gusts near or above 50 mph preceding the line due to the strong pressure gradient. Even more unusual than that? CAE saw its 3rd largest drop in surface pressure over a 24h period, only behind The "Storm of the Century" in 1993 and Hurricane Hugo.

The Bamberg tornado was brief and strong, striking downtown Bamberg directly during the early afternoon hours. Rated EF2, it quickly pushed through the city and caused significant damage to the downtown areas. Thankfully, there were no injuries!

All in all, this was a really impactful way to begin the new year.

We will go from one of the better forecasts by models in recent memory to one that was a real struggle for forecast guidance to pick up on until right before the event itself. The January 27 severe weather event was unique, including the development of multiple classic supercells that pushed across the region.

The setup was a weaker version of one we have seen multiple times this winter already, with a 500 mb shortwave trough pushing into the Mid-MS Valley and OH Valley through the day, gradually taking on a negative tilt. Wind fields were not nearly as impressive as they were with the January 9th system, which will play a role in the kind of storms and severe weather we had this day.

The lack of strong upper-level winds did lead to weaker winds as a whole in the lower portion of the atmosphere, with 850 mb flow generally 15-30 knots during the day, which is much weaker than we see with typical winter time severe weather systems.

We had been very warm in the days preceding this, and with few fronts pushing through, rich moisture was able to build in advance of this system.

The combination of anomalously high 850 hPa dewpoints, surface dewpoints in the low to mid-60s, and some breaks in the clouds allowing temps to rise to near 70F led to fairly significant instability being realized south of the front. This is especially true when you put it in the context of this being a January event!

As unusual as this is, the biggest question was the quality of the wind shear present. The day saw multiple supercells at different parts of the day, with the earlier storms being well ahead of the best deep layer shear and forcing. And this bears itself out when you look at the RAP analysis that day, or even the sounding above! Wind shear profiles were very poor anywhere not right next to the warm front. And luckily for us, the warm front was sitting directly over or near the radar that day. This gave us a good look into what the vertical wind profile looked like in the vicinity of the front.

This wind profile is much different than the wind profile in the RAP sounding (taken in the warm sector) above, revealing the impact that the warm front had on the storm intensity and organization. This also explains why these storms didn't do anything other than produce tornadoes (3 weak, brief tornadoes each in the vicinity of the warm front) - deep layer shear was weak, with almost all of it confined to the lowest 1km.

The first tornado of the day was associated with a supercell that slowly organized over an hour before interacting with the warm front. It began to ingest much better low-level shear as it approached the Columbia Metro area, organizing into a supercell in central Lexington County. About 1 hour later, it produced a brief, EF1 tornado near Elgin SC.

This supercell was the first of several to develop and move across the forecast area on January 27th, and produced one of 3 brief tornadoes from this day.

While this storm followed quickly behind the Elgin storm, it did not produce a tornado. However, that doesn't mean it wasn't a strong storm in its own right. The storm was on the southern end of a cluster of storms that began to intensify once interacting with the warm front draped across the central Midlands. ZDR (differential reflectivity - helps differentiate between precipitation particle size and shape) is a very useful radar parameter and can reveal where very intense updrafts are before reflections of high radar reflectivity materialize. In this storm, a ZDR column had formed and extended above the -20C line in the atmosphere - indicating a very strong updraft, even while reflectivity was only high below 20,000 feet.

The updraft acquired extra low-level shear and became a mesocyclone as it pushed into the greater Lexington area. This storm was so close to the radar, that it proved pretty difficult to get good radar scans on it at lower elevations. We normally like to look at much lower scans like 0.5 degrees and 0.9 degrees for these storms, but because of the proximity to the radar, looking higher up in the storm was the best way to see its true structure. The radar loop on the right is from radar scans at the 3.1-degree tilt, meaning the storm was being sampled between 1800' and 3600', losing some of the clutter that the lowest scans are impacted by. As it moved over the populated areas of Lexington and Richland counties, it yielded some incredible pictures.

So...why did this storm have similar characteristics to the Elgin storm but not produce a tornado? Well, as we found out after the event, the low-level air was way too stable due to widespread rain that had preceded this and pushed the warm front just a bit too far south. This stability was marked by reports of ground fog in central Lexington County. What all of this means is that the storm wasn't able to lift enough air in the updraft to successfully yield tornadogenesis, and thus it was just another unusual and pretty storm!

As the parent upper-level trough slowly worked its way toward the forecast area, it brought a bit more forcing toward the area. As an area of decaying prefrontal convection pushed into Georgia, instability developed ahead of it. With an increase in forcing & instability, thunderstorms developed within the previously decaying area of showers. As these storms were closer to the upper level forcing, better deep layer shear allowed for the storms to have consistent mesocyclones even away from the warm front.

But the warm front was critical in both of these storms producing tornadoes, as they only achieved this as they approached the warm front which was still draped across Saluda county. Thankfully the tornadoes were very weak and short-lived. Overall, these two storms and tornadoes capped off an odd event that models did not anticipate well until the day of. It was also odd that the supercells produced no severe weather outside of the three tornadoes that developed on this day.