March 17, 2021

A Rare "High Risk" Severe Weather Outbreak Is Expected In The Southeast On Wednesday


A significant severe weather outbreak will unfold across the southeastern United States on Wednesday and Thursday, bringing the potential for strong, long-lived tornadoes, as well as many instances of large hail and widespread damaging wind gusts. Wednesday is a rare "high risk" day in the Storm Prediction Center's severe weather outlook, highlighting the seriousness of the threat posed by storms in the southeast. If you live anywhere between Texas and Virginia, make sure you have a way to receive severe weather warnings over the next few days.

The Risk


The Storm Prediction Center's update early Wednesday morning paints a rare high risk for severe thunderstorms—a full 5 out of 5 on the categorical scale measuring severe weather risk—across portions of northern Louisiana, north-central Mississippi, and western Alabama. Forecasters at the SPC don't issue high risks lightly. This is an "alarm bells ringing" moment for folks in the south, the kind of severe weather potential that's keeping meteorologists and weather enthusiasts awake tonight with nervous stomachs.

Don't just focus on the high risk area. Moderate risk (4 out of 5) and enhanced risk (3 out of 5) zones extend outward to cover a significant portion of the southeast, each denoting a significant risk for severe weather in their own right. "Moderate" is a bit of a misnomer when it comes to these categorical outlooks. A moderate risk is a 4 out of 5 on the scale measuring severe weather risk. That's a pretty big deal, and it covers a pretty big area!

To highlight the area of concern on Wednesday, here's a look at the tornado risk during the afternoon and evening hours:


These probabilities may seem a little low, but a 2 percent chance means there's a 2 percent chance of seeing a tornado within 25 miles of any location in the highlighted area. That's not nothing you consider we're talking about a tornado. Meteorologists grow concerned when the tornado risk reaches 5 percent, and it's a serious weather day when the probabilities grow to 10 percent or higher in the SPC's outlook.

The shaded hatching indicates the risk for strong, long-lived tornadoes, the type that can stay on the ground for many dozens of miles before finally lifting. The environment is primed for an extremely dangerous severe weather event.

The Setup

Source: NOAA/WPC
A budding low-pressure system over western Texas and Oklahoma will set the stage for the active weather coming up. The low will strengthen as it heads toward the Mid-South during the day on Wednesday. Warm, humid air will race northward from the Gulf of Mexico, providing the instability necessary for thunderstorms to thrive once they bubble up.

Meanwhile, a few thousand feet above the surface, winds will be tearing along out of the west and southwest. The sharp change in the speed and direction of the wind with height will allow thunderstorm updrafts to begin rotating, creating supercell thunderstorms. The rotating updraft in a supercell makes those storms strong and durable, capable of surviving for many hours while they produce large hail, damaging winds, and tornadoes.

The Threat

This won't be a clean severe weather outbreak where one line of storms moves through and it's over. There will be multiple rounds of storms throughout the day and evening hours, and each round will carry its own predominant hazards.

As these events usually go during a classic springtime outbreak in the southeast, the day will start with discrete thunderstorms in the afternoon that could easily develop into supercells capable of producing tornadoes and large hail. Later on in the evening and overnight hours, a squall line will develop ahead of the cold front and pose one final risk for severe weather, with damaging straight-line wind gusts and quick tornadoes the main threat.

These thunderstorms will move quickly. It won't be uncommon for a single thunderstorm to move 45+ MPH, which reduces your reaction time if you find yourself in the path of a storm. That's why it's so important to stay tuned to the weather and get warnings as soon as they're issued.

Many of the storms will occur after sunset on Wednesday, which packs the one-two punch of catching people while they're sleeping and making it hard to spot tornadoes before they arrive. Tornado chasing and tornado gawking in the southeast is a terrible idea to begin with because there are so many trees and tornadoes here are usually obscured by heavy rain. I used to live in Mobile. I know the impulse to look outside to see if you can see the tornado. Don't do that. A tornado warning means that someone already spotted the rotation or the tornado for you. Trust them and do what you need to do to get to safety.


Oh, and don't fret about comparisons to past outbreaks. It's really hard to get all the ingredients to come together just right to create a historic tornado outbreak like we saw in 2011. Every tornado threat is dangerous in its own right, so take every storm and every warning seriously.

Thursday


The threat doesn't end on Wednesday night. Another hallmark of major southeast severe weather outbreaks is that they continue the following day in Georgia and the Carolinas. A moderate risk for severe weather is in place for much of Georgia, South Carolina, and North Carolina in anticipation of strong tornadoes, widespread damaging winds, and large hail during the day on Thursday. It's rare for the SPC to issue a moderate risk for this area so far in advance, so this is also a big deal. Pay attention.

How To Prepare

The best way to prepare for severe weather is to have a way to receive warnings the moment they're issued. No matter where you live, even if you're reading this from some chilly town up in New England, take a second to check your phone and make sure that emergency alerts are activated for tornado warnings.

These are push notifications that pop up and screech at you if you're within a tornado warning issued by the National Weather Service. They only pop up if your location (really, the nearest cell phone tower's location) is within the warning polygon drawn on a map by an NWS forecaster. This means won't get notified for storms on the other side of the county unless they're headed your way in the next few minutes.

Remember that the goal of tornado safety is to protect yourself from flying debris. That's why they urge you to get to the lowest floor and in an interior room, putting as many walls between you and the outside as possible. It doesn't stop there, though. Wear a helmet if you have one. Even a simple bicycle helmet can help protect your head from flying debris. Also, wear jeans and closed-toe shoes in case you have to walk through debris. I've slept in my jeans and socks before in case I had to jump out of bed for a tornado warning. It's uncomfortable, but it's worth it.

*I apologize for any typos or strange errors in the text. I am my own editor, it's the middle of the night, and I haven't slept in six years.

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I graduated from the University of South Alabama in 2014 with a degree in political science and a minor in meteorology. I ran Gawker's The Vane for two years and I've contributed to Mental Floss, Forbes, Popular Science, and the Washington Post's Capital Weather Gang. I also teamed up with Outdoor Life to write a book called The Extreme Weather Survival Manual, which came out in October 2015.

2 comments:

  1. Here's how the watch levels usually shake out in weather warnings:

    NONE - Maybe once a year you will end up in a warning box if the season is right. When this happens, it will not always be preceded by a watch.

    MRGL - You may see yourself in a watch box (about 1/3 of the time)

    SLGT - You can expect to spend some time in the watch box. Warnings are not very likely.

    MDT - You can expect to be under a warning and you may get hit (at least by the associated severe thunderstorm).

    HIGH - You can expect to be under a warning, and you will probably get hit (at least by the associated severe thunderstorm). There are good reason that school districts in the South will close on such days.

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  2. This is my experience in Indiana. "Not very likely" means a 10% - 40% chance.

    ReplyDelete