Thunderstorms

Deadly Tornadoes Strike The Southeast

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Storm Reports by Location

A catastrophic EF-3 tornado tore parts of Alabama and Georgia today, leaving at least 23 people dead and many others injured. This tornado was part of a larger early-season outbreak that brought at least a dozen tornadoes to Alabama, Georgia, Florida, and South Carolina.

These tornadoes were formed when an intensifying low-pressure-system over the Southeast pulled warm, moist, southerly winds from the Gulf of Mexico while a strong, westerly jet stream moved over the same region, creating mild instability and strong wind shear. Once the relatively high March sun angles warmed the surface and destabilized the atmosphere, it didn’t take long for thunderstorms to form. And with so much wind shear in the lower and mid-levels of the atmosphere, it wasn’t long before these thunderstorms evolved into rotating, tornadic supercells.

Dixie Alley:

In contrast to well-known “Tornado Alley” over the Plains, the deep Southeast is known as “Dixie Alley” and is also a tornado hot-spot in the U.S. While Dixie Alley sees fewer tornadoes than Tornado Alley, Dixie Alley has a higher proportion of violent, long-lived tornadoes than Tornado Alley. And because the Southeast has a higher population density and higher percentage of mobile/manufactured homes than the Great Plains, Dixie Alley states tend to see more tornado fatalities than the Plains states, with the exception of Texas.

Dixie Alley Map
Credit: Wikimedia contributor Bhockey10

In doing some research for this blog, I was somewhat surprised to find that that Alabama was tied with Oklahoma for the highest number of F5 or EF-5 tornadoes since 19501. While the Southeast generally does not have the amount of instability (as evidenced by the relative lack of large hail) that the Plains have and does not have the regular occurrence of a “dryline” along which tornadoes commonly spin up, it is a favored formation region for strong mid-latitude cyclones, and the combination of strong, low-level, southerly flow from the Gulf of Mexico and cold, westerly flow aloft provides enough instability and, more importantly, tons of lower-level wind shear and helicity (the tendency for air to spiral upward in a helical manner) to support supercell thunderstorms with long-lived, violent tornadoes.

The 3/3/2019 Outbreak

Like many Dixie Alley outbreaks, the Sunday 3/3/2019 tornado outbreak was associated with a deep upper-level trough and a developing surface low over the Southeastern US. This upper-level trough provided the surface convergence/upper-level divergence (something I won’t get into here!) to spur the formation of this low-pressure system, and the combination of low-level, mild and moist southerlies in response to the developing low and the cold, strong westerlies aloft created an unstable atmosphere with lots of wind shear.

GOEDS-16 water vapor
GOES-16 lower-level water vapor image at 2:57 pm EST. The EF-3 Beauregard supercell/tornado is the southeastern-most green blob over extreme eastern Alabama.
Credit: CIRA

Strong thunderstorms began to form in the late morning, and several of these quickly turned into tornadic supercells by the early afternoon. The strongest storm by far was a high-end EF-3 storm that hit the community of Beauregard in Lee County, Alabama and continued tracking towards northern portions of Columbus, Georgia. This tornado alone killed 23 people, more than double the death toll of all of 2018’s tornadoes combined. And with others still missing, the death toll may rise in the days to come.

The radar image below shows the well-defined “hook echo” with this storm as it tracked over Lee County. Hook echos are formed when the thunderstorm’s updraft is rotating so violently that it partially wraps the precipitation-laded downdraft around the updraft, creating a “hook.” Tornadoes are generally found at the very tip of the hook, and there is often an area of increased reflectivities on radar due to the debris cloud associated with the twister.

Beauregard Hook Echo
Hook echo from the supercell as it passes near Beauregard, Alabama (not labeled on the map)
Created with NOAA Weather and Climate Toolkit

Well over a dozen other tornadoes were recorded throughout Alabama, Georgia, Florida, and South Carolina. There have been 38 storm reports thus far today from the National Weather Service, though I’m not sure how many of these reports are of the same tornado.

Storm Reports by Location
3/3/2019 Storm Reports by location
Credit: Storm Prediction Center
Storm Reports Graph
3/3/2019 Storm Reports by time
Credit: Storm Prediction Center

Finally, here are some pictures/damage reports on Twitter. It’s heartbreaking to see all the devastation there… I am frankly at a loss for words.

Emergency Preparedness and Forecast Communication:

One of the reasons why scenes like these are so troubling is that there is so much low-hanging fruit when it comes to giving more precise and accurate tornado warnings. Many towns in Dixie Alley do not even have tornado sirens, leaving the public unaware of a tornado warning in their area. Additionally, the Southeast has some of the worst radar coverage east of the Continental Divide. Poorer radar coverage means that meteorologists have (1) less visibility of the lower atmosphere (the lowest radar beams are generally angled at 0.5 degrees, meaning the beam travels upward the further distance it is from the radar) and (2) less spatial resolution and therefore less insight into the structure of potentially tornadic thunderstorms. This results in a false alarm rate for approximately 85% of tornado warnings, resulting in a desensitized populace that may be slow to take action when a life-threatening tornado is on the ground.

Even worse, these radars fail all too often. In fact, the Macon, GA radar failed today during this tornado outbreak.

By simply having more tornado sirens and better and more reliable radar coverage, we would be able more effectively communicate tornado warnings and have fewer false alarms, hopefully saving lives in the process.

I know that’s a somber note to begin your week, but I hope you found the analysis interesting, and I promise my next post will be a little more upbeat!

Charlie

  1. https://weather.com/storms/tornado/news/2018-05-01-violent-tornado-states

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