Severe weather to sweep through Plains, South, Mid-Atlantic midweek

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As the storm system sweeps across the country, Wednesday is predicted to be the nastiest day for thunderstorms and could feature a squall line with damaging winds and embedded tornadoes that blows through Mississippi and Alabama. An isolated strong tornado is possible if additional rotating thunderstorms develop ahead of the main line, though there is high uncertainty.

The severe thunderstorm risk commences on Tuesday in the Plains, and should end Thursday evening in the Mid-Atlantic.

March often kicks off a three-month stretch punctuated by seemingly ceaseless barrages of severe thunderstorms and tornadoes across the Lower 48. April marks the start of peak tornado season, when a seasonal clash — characterized by warm air from the Gulf of Mexico waging war with chilly lingering wintertime air — brews violent storms.

There are already signs that April and May could be more active than average, meaning severe thunderstorm and tornado chances aren’t likely to flatline any time soon.

Setting the stage for storms

On Monday morning, a counterclockwise swirl could be seen on water vapor satellite imagery moving ashore in Southern California. It was bringing heavy rain and mountain snow.

That marks a shortwave — a lobe of high altitude cold air, low pressure and spin. It will shift east with time and help energize a surface low dropping from the Intermountain West into the central Plains.

On Tuesday, southerly and south-southeasterly winds will be on the increase. That’ll bring in warm air loaded with Gulf of Mexico moisture into the eastern Plains. As temperatures at high-altitudes cool, parcels of air at ground level will begin to rise and form strong to severe thunderstorms.

Meanwhile, the shortwave is nestled within a dip in the jet stream, a river of swiftly-moving air in the upper atmosphere. That wind at upper levels will help amplify wind shear, or a change in wind speed and/or direction with height. That means any thunderstorms that tower through multiple levels of atmosphere will derive a twisting force that will foster rotation.

Dry air brings ‘critical’ fire weather and triggers storms

Storms will form along a dryline Tuesday afternoon, a nose of arid air ahead of the storm system ejecting from the Southwest into the western Plains. The dryline will serve as a triggering mechanism, the impetus for surface air to rise. It will be integral in popping storms Tuesday.

At the same time, the bone-dry air mass in advance of the storm is responsible for bringing “critical” fire weather to the Plains, particularly on Tuesday. The Storm Prediction Center is warning that “a significant fire weather episode is anticipated,” with southwest Kansas, western Oklahoma, western Texas and eastern New Mexico most affected.

The overhead jet stream will help mix down strong winds of 30 to 35 mph with gusts to 60 mph as humidity plummets.

Severe storm risk Tuesday

On Tuesday, severe thunderstorms will form in Oklahoma and north central Texas during the late afternoon or evening. Some may get going a bit earlier in Kansas.

A broad level 2 out of 5 “slight risk” for severe weather has been drawn from near Austin to northeast Kansas, and includes cities like Dallas, Fort Worth, Waco, Oklahoma City, Tulsa, Wichita Falls and Kansas City.

In northern parts of the risk area, dry air aloft might limit storm longevity, meaning shorter-lived “pulse” thunderstorms would be probable with gusty to damaging straight-line winds. Across the Plains, straight-line winds are the main concern, with a sporadic shower of quarter-sized hail possible, too.

Storms may congeal into a line along the Intestate 35 corridor from roughly Dallas to Stillwater, Okla., during the evening and overnight, with a low-end risk for a tornado or two.

Storms move into Deep South on Wednesday

Wednesday’s storms will roll through Mississippi, Alabama and Louisiana, where a level 3 out of 5 “enhanced risk” for severe weather is up. The bull’s eye encompasses Alexandria and Monroe, La., Jackson and Hattiesburg, Miss., and most of Alabama, including Tuscaloosa and much of the Birmingham metro area.

It’s not yet clear how much cloud cover from Tuesday’s storms will be draped across the Deep South on Wednesday, and how much sunlight will be available to fuel storms.

It looks likely that storms will acquire the form of a QLCS, or quasi-linear convective system. That’s a squall line with embedded circulations within it. Damaging winds are likely along the entire length of the line (perhaps in excess of 70 mph), along with some tornadoes.

Only if rotating thunderstorms or supercells blossom in the “warm sector” ahead of the QLCS will there be a formidable hail and significant (EF2+) tornado risk. This depends somewhat on how much sunlight is available before storms develop.

A widespread 1 to 2 inches of rainfall is also possible.

Storminess in Mid-Atlantic on Thursday

By Thursday, the storm system will move into the Mid-Atlantic. While there won’t be a ton of “juice,” or heating for thunderstorms to grow tall, shear will be plentiful. Subsequently, we’re expecting mainly low-topped storms capable of producing isolated to widely scattered damaging straight-line winds.

There’s a level 2 out of 5 slight risk of severe weather in effect for the Interstate 95 corridor that includes Philadelphia, Baltimore, D.C., Richmond, Virginia Beach and Raleigh, N.C.

There’s a chance thunderstorms will be devoid of lightning given how shallow they’ll be.

Cooler air will build in behind the front for the upcoming weekend.

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