South faces outbreak of tornadoes and severe storms for second straight Sunday

Multiple waves of severe thunderstorms are expected Sunday and Sunday night from Texas and Louisiana to the Atlantic coast of the Carolinas as a strong storm system rolls across the area. Accompanying the potentially vigorous storms is the expectation for flash flooding in some areas.

The anticipated outbreak comes exactly a week after more than 130 tornadoes tore up much of the South and Southeast amid a deadly severe weather event. With a preliminary tally of 69 deaths, 2020 has already been the nation's deadliest year for tornadoes since 2012 - and it's only mid April.

Another round of storminess is possible from Wednesday into Friday from the Southern Plains into the Southeast, though details remain uncertain at this time.

The repeated threat of dangerous storms underscores the challenge of living in storm-prone areas during the springtime, and also the importance of having a severe weather plan in place and knowing what to do when the time comes.

"I think Alabamians are tired of dealing with COVID-19, and after last Sunday, tired of dealing with severe weather," wrote James Spann, the chief meteorologist for the ABC affiliate Birmingham in a Facebook post outlining Sunday's severe weather threat. "We don't do this to scare anyone, or make them more anxious, but at the same time we have to let you know there is a risk of severe thunderstorms ... We will get through the day together." 

Spann and other meteorologists having emphasized the importance of having a way to get notified of any warnings issued. A battery-backup NOAA weather radio is ideal while you ensure wireless emergency alerts are activated on your phone, and that "do not disturb" mode is disabled.

- Hazard breakdown

Areas at risk: A large level 4 out of 5 "moderate risk" stretches across the National Weather Service Storm Prediction Center's latest severe weather map. That's where meteorologists anticipate a "regional outbreak of tornadoes and damaging wind," the red zone encompassing a large swath of Louisiana, Mississippi, Alabama, and western/central Georgia.

Included within the moderate risk area are more than 5 million people, including the cities of Jackson, Mississippi; Alexandria, Louisiana; Columbus, Georgia, and Montgomery, Alabama. In addition, the same parts of rural southeastern Mississippi that bore witness to an extreme 2.25-mile-wide EF4 tornado last week are once again in Sunday's highest tier of risk.

Surrounding the moderate risk zone is a blanket of level 3 out of 5 "enhanced" risk, up for cities like Mobile, Alabama; Shreveport, Louisiana; Charleston, South Carolina, and Savannah, Georgia.

A level 2 out of 5 "slight risk" has been drawn on from Houston and Dallas to Birmingham to Atlanta, because confidence in higher-end storms is less there. That's because those areas may lie near where the warm front stalls, preventing them from fully breaking into the explosive air mass that lurks to the south.

Threats: While damaging winds is likely to be the most widespread hazard, the threat of tornadoes will also be noteworthy. Two areas right now have the greatest risk for strong tornadoes:

The first is across central Mississippi and west central Alabama, where a number of downpours and thunderstorms were rumbling through Sunday morning along the cold front. As daytime heating commences and surface temperatures warm, thunderstorm activity in this vicinity will become more vigorous. If, and that's an if, a couple lone rotate supercell thunderstorms can develop near or just south of this warm and remain uninhibited by neighboring storms, the threat for a couple tornadoes, perhaps strong, would manifest itself by early Sunday afternoon.

A second corridor of enhanced tornado activity could exist in southern Mississippi, especially east of Interstate 55, and extend into southwestern and south central Alabama. That's where a pocket of a few supercells, rotating thunderstorms, could develop Sunday afternoon ahead of an approaching line of storms. Any of those supercells will be able to produce damaging wind, large hail, and perhaps strong tornadoes. That again includes the Jackson to Hattiesburg, Mississippi, area, which was struck by violent tornadoes last Sunday.

A hail threat will also accompany clusters of storms, especially in East Texas, southern Arkansas, Louisiana, and Mississippi. A few instances of hail greater than two inches in diameter can be expected there.

Eventually, storms will merge into a line that will produce widespread damaging wind gusts, in some locales topping 70 mph. Southern Alabama and Georgia are particularly vulnerable to that line of storms, which could impact Columbus - including Fort Benning, the Heart of Georgia, Dothan, Alabama, and Montgomery, Alabama. Erratic tornadoes may form along the leading edge of any line of storms.

That line will likely make it to the Atlantic coastline late in the overnight into very early Monday morning, bringing at least widely scattered damaging wind gusts to the Midlands and Beaches of South Carolina, also hit hard by storms last week.

- Flooding concerns

This event also features a substantial risk for flash flooding across central Mississippi, and especially Alabama and western Georgia. Up to 2.5 inches of rain was expected to have already fall by late morning across many of these areas; that could saturate soils and prime the ground for flash flooding if thunderstorms "train" and pass over the same areas during the afternoon and evening. A few areas may wind up with 6 inches or more of rainfall.

- Timing

Heavy rain and a couple strong storms covered the weather map in Alabama and eastern Mississippi early Sunday. The axis of heaviest storm activity will be shunted north a bit by lunchtime, allowing warm, humid air to surge in across areas to the south. That will allow additional storms to develop, and increase in both areal coverage and intensity.

The greatest chance for supercell thunderstorms will come between 2 p.m. and 8 p.m. Central. Thereafter, storms will likely merge into one or more lines, with Georgia coming into play by late day and South Carolina by the overnight into early Monday morning.

- Meteorological setup

The storms stem from a pocket of spinning upper-level cold that was digging south off the California coast as late as Saturday morning. It then swung across the Four Corners region toward the Texas and Oklahoma Panhandles, where it started the day early Sunday. Ahead of this axis of "vorticity," or spinning air, an influx of Gulf of Mexico air will overspread much of the South.

That approaching area of spin will foster rising motion ahead of it, kindling the development of strong to severe thunderstorms. Meanwhile, a surface stationary front draped essentially parallel and just to the north of Interstate 20 between East Texas and South Carolina will serve as a focal mechanism for storms. To the north, a chillier air mass will lend itself to nonsevere storms and heavy rain, while severe weather will flourish in the milder air to the south.

That upper-level pocket of cold and spin is cradled in a dip of the jet stream; ahead of it, a zone of fast-moving air will surge northward. That will help boost the amount of "wind shear" present, or a change in wind speed/direction with height. That increases the chance of rotating storms.