The CIPS Analog product highlights where similar past setups have produced severe weather during events like this. (CIPS/Saint Louis University)

The odds of a significant severe weather episode are increasing across portions of the Southern Plains, Deep South and Southeast late this week into Easter weekend as a potent storm system treks across the country.

The threats include damaging winds, large hail and tornadoes. This storm would arrive as many areas mark the beginning of what’s historically the most active time for tornado activity across the southern United States.

Despite considerable uncertainty days before an event, the Storm Prediction Center is already noting “a substantial severe episode appears possible this weekend, from Texas into portions of the lower Mississippi Valley on Saturday, and especially from the lower Mississippi Valley into portions of the Southeast on Sunday.”

There is also the potential for the Carolinas and Mid-Atlantic region to be affected on Monday, depending on the storm’s exact track.


The American GFS model shows strong winds diving south at the mid levels of the atmosphere, probably enhancing severe weather this weekend. (WeatherBell)

The threat comes at a challenging time, when stay-at-home orders are the norm and social distancing to halt the spread of the novel coronavirus poses a challenge for those forced to rely on community shelters. A number of states have grappled with whether to open community storm shelters amid fears of covid-19.

The setup

Instigating the potentially dangerous weather will be a low pressure system ejecting out of the Intermountain West early Friday, moving southeast and emerging over the High Plains toward eastern Colorado, western Kansas and western Nebraska overnight Friday into Saturday.

To the east of the low, southerly winds will transport a warm, humid air mass northward over Texas, Oklahoma, Arkansas and Louisiana.

Trailing the low will be a “dry line” stretching down to the Rio Grande Valley in Texas. That’s the boundary between moisture-rich air to the east and encroaching dry, desert air from the west. That boundary will serve as a focal mechanism for shower and thunderstorm growth, and ultimately be one of the triggers for potential severe weather at the start of the event.

Saturday

Strong to severe thunderstorms will be possible across much of Texas, including the Dallas-Fort Worth Metroplex, on Saturday. The risk could extend as far north as the Red River that separates the Lone Star State from Oklahoma. By late Saturday, storms could reach into southwestern Arkansas and western Louisiana.

There is uncertainty Saturday regarding how far north the severe thunderstorm risk will extend.

Sunday

Sunday looks to feature an even greater probability of severe weather, especially from southern Arkansas and Louisiana into most of Mississippi and Alabama. Western Georgia could come into play late in the day.


The American GFS model shows dry air (brown) shunting moisture (green) eastward this weekend. The clashing air masses could generate severe weather along and ahead of the boundary. (WeatherBell)

The atmosphere will also be more conducive to tornadoes forming on Easter. Just a few thousand feet above the ground, a strong southerly low level jet stream will transport an uninterrupted moisture supply from the Gulf of Mexico, while at the mid-levels winds will be more southwesterly or westerly.

That change of wind speed and direction with height, known as “wind shear,” is one of the key ingredients necessary for tornadoes to form.

Flooding over Mississippi, Tennessee Valleys

Also of note with the system is the flood risk that exists over portions of the central Mississippi and Tennessee Valleys. A stalled stationary front separating warm air to the south and cooler air to the north could help to focus heavy downpours wherever it becomes established, likely in Tennessee, northeastern Mississippi, northern Alabama, and northwest Georgia. It’s already been a very wet start to the year for many of these areas, and additional flood concerns may come into play on Sunday.

Risk on Monday is highly uncertain

Monday is a major wild card regarding the storm threat. An earlier frontal passage would result in a few showers or lower-end thunderstorms for some in the Southeast and southern Mid-Atlantic, but without daytime heating to foster rising motion in the atmosphere, the risk of severe weather would be low.

However, if the storm system lags behind a few hours later and approaches the Mid-Atlantic in the afternoon, another wave of strong to severe thunderstorms could be possible over the coastal Southeast, Carolinas and possibly into the Mid-Atlantic.

“The first option is that the system tracks to our south, but we are solidly within the heavy rain threat, so flooding concerns could arise,” wrote the National Weather Service office in Washington, D.C. “The other possibility is for the system to track into the Ohio Valley, and bring a cold front through late Sunday or Monday … which would result in the potential for some severe weather.”

Action items

The bottom line remains that a significant severe weather event appears to be growing in likelihood for many. It’s imperative to have a severe weather plan in advance, and know where you will seek shelter if a particular weather warning is issued.

In light of recent events, it’s also important to check beforehand to ensure your shelter of choice, such as a community shelter, will be open. Some shelters have been shuttered for fears of spreading the coronavirus, while officials in other states — including Alabama — have listed tornadoes as a more “immediate” threat.

Following the storms, a brief cool-down is expected, but it’s worth noting that April and May have climatologically proved some of the most active months for severe weather.