Severe storms roll across South, Southeast before sparking on Plains

WEATHER NEWS: Severe storms roll across South, Southeast before sparking on Plains

Tornado watches blanketed much of the Gulf Coast from southeastern Louisiana to the Florida Panhandle on Tuesday morning into the afternoon. Through late morning, the National Weather Service had received five reports of tornadoes in Mississippi and Alabama, with numerous trees and power lines down as well as some structural damage near Newton, Miss., which is between Jackson and Meridian.

“A swath of damaging wind gusts and several tornadoes are possible across the region, including the risk of a strong tornado,” the Weather Service’s Storm Prediction Center wrote.

Warnings for radar-confirmed tornadoes were in effect east of Montgomery, Ala., around 11:15 a.m. local time through around midday.

Thunderstorms will continue rolling all the way to the coastal Carolinas by late Tuesday. Severe storms will be most numerous in the Southeast on Wednesday, while another round from a second system is possible in the southern and eastern Mid-Atlantic on Thursday.

There already are signs that a robust severe weather event may occur early next week, with the first potentially large-scale classic spring event striking the Plains. Conditions look broadly supportive for tornadoes, and it’s probably just a taste of what’s ahead in the second half of April and much of May as severe-weather season enters its prime.

Storms roll through Texas, enter South

Thunderstorms first formed in north-central Texas on Monday evening, bringing reports of damaging straight-line winds and hail around the Dallas-Fort Worth area. Half-dollar-size hail was reported a mile north of Propwash Airport in Denton, and parts of the area around Dallas were placed under a tornado warning around 11:15 p.m. Monday.

A tornado was confirmed by radar at 10:55 p.m. in northern Johnson County, due south of Fort Worth. The circulation crossed Interstate 35W shortly after that. Radar also indicated straight-line winds near 80 mph were contained in the storm as it barreled through northwest Ellis County.

The storms that hit Texas have since merged into an MCS, a mesoscale convective system. That’s a large complex of thunderstorms that takes the shape of an arcing squall line, propelled forward by strong winds aloft and the outward surge of cool air descending in its wake.

A number of tornado warnings were in effect in southern Alabama on Tuesday morning as the complex continued to sag south and east.

Afternoon storms are likely to be further invigorated by multiple factors. Heat from the sun will help warm the ground just enough to fuel intensifying storms. Simultaneously, a warm front will lift northward during the day.

North of the warm front, storms are “elevated,” rooted within a layer of warmth resting atop cool surface air. That leads to mainly heavy rain producers with sporadic hail. The risk of damaging winds and tornadoes will blossom in the “warm sector” later on as warm, moist air occupies more real estate.

Tuesday’s storm risk at a glance

  • Areas affected: The Storm Prediction Center had drawn a Level 3 (out of 5) “enhanced risk” of severe weather on its outlook map for much of southern Alabama, Georgia and South Carolina. Cities such as Montgomery, Mobile and Dothan, Ala.; Columbus and Savannah, Ga.; and Charleston, S.C., were included in that risk tier. A marginal to slight risk of severe weather wraps around it from North Carolina’s Outer Banks to near Lake Okeechobee in Florida.
  • Timing: Ongoing thunderstorms Tuesday will strengthen as a warm front lifts north during the afternoon and evening. Thunderstorms may reach the coast of Georgia and South Carolina by 9 or 10 p.m.
  • Hazards: Damaging straight-line winds gusting up to 60 mph are the primary hazard, with scattered quarter-size hail and isolated tornado activity. A few instances of large hail are possible with the elevated storms north of the warm front; egg-size hail smashed through windshields in Linden, Ala., before sunrise Tuesday.
  • Areas impacted: A Level 3 enhanced risk is up for northern Alabama, northern Georgia and southeastern Tennessee, including Birmingham, Atlanta and Chattanooga. A more expansive Level 2 slight risk stretches from southern Kentucky through the remainder of Alabama, Georgia and South Carolina and dips into the Florida Panhandle.
  • Timing: The specific timing and evolution of storms will hinge on what transpires with Tuesday’s storms and how the atmosphere recovers. That said, thunderstorms are more probable in the afternoon and evening.
  • Hazards: Rotating thunderstorms or supercells aren’t generally expected, but lines or bowing segments capable of producing damaging straight-line winds or an isolated tornado are possible.
  • Areas affected: Thunderstorms on Thursday will probably be confined to extreme eastern parts of North Carolina and perhaps southeastern Virginia. That’s where a Level 2 slight risk has been drawn. Norfolk, Virginia Beach and Wilmington, N.C., are affected.
  • Timing: Timing is critical. Morning storms to the north might “work over” the air and sap much of the juice from it, but if the front slows down just a tad or the “warm sector” can become better established, severe-weather chances would climb. Any severe weather should probably hold until 3 p.m.
  • Hazards: Storms are likely to be structured as a broken line, but a seasonably strong jet stream aloft, with air racing northward at highway speeds barely a mile above the ground, will be present. Any thunderstorm that taps into that momentum aloft will be able to transfer it to the surface in the form of strong to locally damaging wind gusts.

Another round of strong to severe thunderstorms will commence Monday. The jury is out on the specifics, but a few ingredients appear to portend storms on the Plains.

A dry line, or the leading edge of arid air from the Southwest desert, will sharpen along the I-35 corridor in south-central Kansas, Oklahoma and northern Texas on Monday. Ahead of it, moisture-rich air from the Gulf of Mexico will be in place. Strong upper-level winds from a dip in the jet stream will accompany an upper-air disturbance, setting the stage for storms.

It remains to be seen whether wind shear, or a change in wind speed or direction with height, is adequate to support tornadoes. Regardless, expect an uptick in severe weather over the Lower 48 toward the start of the next workweek.

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