Dangerous storms target South today ahead of severe outbreak Monday

Tornado watches cover southern portions of Mississippi and Alabama and the western Florida Panhandle into the afternoon.

The threat of severe weather will visit the Southeast and Mid-Atlantic on Saturday, with straight-line winds and a tornado or two possible.

Then a more significant severe weather outbreak will loom Monday, Tuesday and Wednesday, the multiday onslaught of storms set to track from Texas to the Southeast. There are signs that the hazardous storms could be widespread. It’s all part of an active pattern that looks to usher in April.

Tornado watches were up overnight in southeastern Louisiana and southern Mississippi from the New Orleans metro area to near Biloxi and Gulfport. A line of thunderstorm clusters and embedded pockets of rotation was shifting to the east toward Alabama and the Florida Panhandle. Those regions will be affected by storms through the early afternoon as a warm front lifts northward.

Thus far, thunderstorms were less intense than originally forecast, for two reasons:

• Low surface temperatures. The warm front was providing laggard in its northward journey, failing to deliver mild, moisture-rich surface air to most of south-central Mississippi or Alabama ahead of a line of encroaching thunderstorms. That will keep thunderstorms “elevated,” or rooted in air above the surface layer, and mitigate a threat of tornado/damaging winds.
• Boundary-parallel flow. Air at the low to mid-levels was largely parallel to the line of thunderstorms, which meant that any new updrafts formed primarily along the line of advancing storms rather than ahead of it. That resulted in a line of thunderstorms rather than more fierce individual storm cells capable of robust rotation.

While it’s unclear whether thunderstorms will evolve in a way to allow them to fully tap into the hostile dynamics of the atmosphere, the greatest threat of severe weather through the early Friday afternoon will remain in southeastern zones near Interstate 10 in southern Alabama and the Florida Panhandle. .

Assuming skies clear and the ground heats up behind morning storms, there could be an afternoon round in central Alabama and perhaps Tennessee. Strong winds, hail and an isolated tornado are possible with any afternoon storms.

Farther north, there will probably be some rotating thunderstorms in Kentucky, southeast Illinois and southern Ohio along the Ohio River. These will be spinning especially since they’ll be near approaching low pressure, but they’ll be low-topped. Subsequently, hail looks like the primary risk (with a few hailstones perhaps approaching lime size), with a secondary risk of damaging winds or an isolated tornado.

On Saturday, the threat will shift toward the East Coast. A level 1 or 2 out of 5 marginal or slight risk of severe weather stretches from the Finger Lakes of New York all the way south to northern Florida. The threat may be maximized in the Mid-Atlantic from the Delmarva Peninsula to the Virginia Tidewater and parts of the North Carolina Coastal Plain.

That’s where there’s an acute risk of a brief tornado with any storms that form there. Otherwise, like locally damaging winds are expected within storms.

While there is plenty of shear, or a change of wind speed/direction with height, for storms to work with, there is also a “cap” of warm air that will be in place several thousand feet above the ground. This will tamp down thunderstorm chances by preventing surface pockets of air from rising. Therefore, storm coverage will be isolated to widely scattered, but that may make for greater intensity within the storms that do form.

The storm risk should tend to focus east and southeast of Richmond, Washington and Baltimore, but these cities should monitor forecasts.

Monday through Wednesday risk next week

The greatest risk of severe weather over the next week comes Monday through Wednesday, when a shortwave — or high altitude lobe of cold air, low pressure and spin — will swing across the South and carry with it an arsenal of disturbed weather. The system will eject out of New Mexico into West Texas early Monday, its chilly air aloft encouraging pockets of surface air to rise.

At the same time, a dry line will sharpen near or just west of Interstate 35 in east Central Texas. That’s the leading edge of arid air from the Desert Southwest as it encroaches on gulf-moistened air to the east. That contrast between dry and humid air masses will serve as the impetus for storms, focusing them on an axis that will shift east.

Because the instigating upper-air system is nestled within a dip in the jet stream, there will be copious wind energy a few thousand feet above the ground. That will give storms the potential to produce damaging gusts, as well as amplify wind shear and encourage storms to rotate. Damaging winds, hail and tornadoes, a few significant, are likely.

On Monday, the threat is greatest in East Texas from roughly Dallas to northwest of Houston. The Storm Prediction Center has drawn a level 3 out of 5 enhanced risk for severe weather and may upgrade to a level 4 out of 5 risk as the event nears. Cities including Waco, Tyler, Bryan, College Station and Longview are in the bull’s eye, although Austin, Galveston and a number of others are included in the broader slight risk.

Storms move east Tuesday into eastern Louisiana and Mississippi, which are within an enhanced risk zone for severe storms. Jackson, Meridian and Vicksburg in Mississippi are in line for dangerous thunderstorms.

Parts of the Southeast, including eastern Alabama and western Georgia, are in play on Wednesday. Montgomery, Ala., Columbus, Ga., and Tallahassee are included in the risk zone.

Thereafter, comparatively tranquil weather looks to build in for a few days, but there are signs that March could end with more active severe weather across the southern United States.