Severe storms, tornadoes, threaten Texas, Louisiana, Southeast

WEATHER NEWS: Severe storms, tornadoes, threaten Texas, Louisiana, Southeast

The storm system first affects the Lone Star State on Monday, then expands into Alabama, Georgia and perhaps even South Carolina on Tuesday. By Wednesday, more severe weather eyes parts of Alabama, Georgia and Tennessee before a threat shifts into the southern Mid-Atlantic on Thursday.

Thereafter, the upcoming weekend appears quiet with regard to severe weather potential across the Lower 48, but signs point to a reinvigoration of active weather come Monday or Tuesday of next week.

The months of April, May and June tend to be the most active for tornadoes in the United States; it’s quite typical for hundreds to spin up during that three-month span. A seasonal clash of air masses — the building warmth of summer juxtaposed against the leftover bitterness of winter’s chill — wages war over the Plains and the Gulf Coast states.

Current outlooks indicate this year’s meteorological caprice, and resultant ferocity, may be bolstered by mild Gulf of Mexico water temperatures and a lingering La Niña pattern. The latter frequently alters the position and strength of the jet stream into a favorable setup for severe thunderstorms in the south-central and southern United States.

Broad flow from the south will allow warmth and moisture to become established over the southern and south-central United States during the first several days of the workweek. At high altitudes, however, a pair of disturbances known as shortwaves will approach from the west. Shortwaves are lobes of high-altitude cold air, low pressure and spin.

The first is a relatively weak, decaying one that is pivoting around a larger bowling-ball-shaped zone of low pressure over the Pacific Northwest. It will touch off thunderstorms along a Texas dryline, or the boundary between arid air encroaching from the Desert Southwest and humid air wafting in from the Gulf.

Thunderstorms will probably merge into a larger “mesoscale convective system” (MCS), or a complex of thunderstorms with strong winds, that will roll across the South on Tuesday. Additional MCS activity will occur Wednesday into Thursday over the Southeast, the Carolinas and parts of southern Virginia.

  • Areas impacted: A level 3 out of 5 “enhanced risk” of severe weather is up Monday for much of northeast Texas, northern Louisiana and extreme western Mississippi. Dallas; Fort Worth; Jackson, Miss.; Shreveport, La.; and a broad stretch of Interstate 20 are included in the zone of greatest concern.
  • Summary: Thunderstorms will fire first along the dryline in north Central Texas before quickly merging into a cluster. A few of the initial cells southwest of Abilene toward San Angelo might develop as isolated rotating thunderstorms or supercells, but the majority of thunderstorms will clump together quickly. Then they’ll push southeast overnight with a continued threat of damaging wind.
  • Timing: Most of the storms won’t crop up until around the evening commute. From there, they’ll hit Dallas-Fort Worth around nightfall and enter northwest Louisiana overnight.
  • Hazards: Damaging straight-line winds gusting to 60 mph are the main hazard, but an isolated short-lived tornado can’t be ruled out within “kinks in the line,” or embedded circulations.
  • Areas impacted: A level 3 out of 5 “enhanced risk” of severe weather has been drawn by the National Weather Service Storm Prediction Center for a lengthy swath of the South. It stretches from southeast Mississippi through southern Alabama and Georgia and into South Carolina. Montgomery, Ala.; Columbus, Macon and Savannah, Ga.; and Charleston, S.C., are all included.
  • Summary: Uncertainty is high with regard to the evolution of remnant morning storminess over Louisiana stemming from Monday’s storms. When the sun rises, it may rejuvenate the first line of storms, or if sunshine breaks out behind the thunderstorms, the ground may become heated enough to support a second round.
  • Timing: Storms will be ongoing in the morning in western regions of the risk area, moving east with time. It’s unclear whether a second line of storms will develop.
  • Hazards: Damaging straight-line gusts to 65 mph, along with a couple of tornadoes. These would be of the QLCS, or quasi-linear convective system, variety. QLCSs are squall lines that can have embedded areas of spin that can produce tornadoes; QLCS tornadoes are usually, but not always, short-lived and of the weaker variety.
  • Areas impacted: Birmingham, Atlanta and Chattanooga, Tenn., are in a level 3 out of 5 enhanced risk for severe weather. A larger level 2 out of 5 slight risk stretches from southern Kentucky and the Appalachians to the Gulf Coast.
  • Summary: A warm front will lift north, allowing mild and humid air to spread over areas as far north as the North Carolina-Virginia border by evening. That will offer ample fuel for thunderstorms that form along a cold front sagging in from the northwest. Once again, thunderstorms will probably take the form of a QLCS.
  • Hazards: Damaging straight-line winds and a few tornadoes, as well as isolated flooding in parts of northern and central Alabama that see multiple days of storms in a row.

On Thursday, thunderstorms will probably continue in parts of eastern North Carolina and Virginia, with an attendant risk of damaging winds. An exceptionally strong jet stream will be racing overhead, and thunderstorms could mix some of that momentum to the surface.

Looking ahead, the next widespread chance of severe weather in the central United States is slated for Monday, when a classic Plains dryline setup looks to materialize. A robust shortwave will energize a fledgling surface system, priming the atmosphere for severe thunderstorms in Oklahoma and Texas with a risk of tornadoes too. Thereafter, the risk will probably translate east with time.

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