Easter Sunday severe storm outbreak targets South, could spawn a few strong tornadoes

The Storm Prediction Center has issued a moderate (Level 4 out of 5) risk of severe weather for Sunday. (NOAA/SPC)

A severe weather outbreak is expected for much of the South this Easter weekend, with damaging winds and the possibility of a few strong, long-track tornadoes as a potent storm system marches across the nation.

More than 80 million people could be affected in an area that stretches from Texas to the Gulf Coast and northward to the Mid-Atlantic as waves of severe thunderstorms race east. Others in the Tennessee Valley and Appalachians are in jeopardy of dealing with flash flooding, with heavy rains expected to drench areas that have already seen a soggy start to the year.

Easter Sunday will feature the most dangerous weather for parts of the South — including Arkansas, Louisiana, Mississippi and Alabama — with the threat of strong, long-track tornadoes where conditions line up just right.

The Storm Prediction Center has placed this region under a moderate risk of severe weather, a Level 4 out of 5 on its scale. In addition to the tornado threat, a powerful squall line could bring widespread damaging winds.

The outbreak comes at a difficult time for warning people in harm’s way. Not only is it a holiday weekend, but there’s also the coronavirus pandemic. In an era of social distancing concerns and stay-at-home orders, some meteorologists are finding it more challenging than ever to communicate the importance of having a severe weather plan — even if that may involve sheltering with others.

Saturday
The Storm Prediction Center has issued an enhanced risk (Level 3 out of 5) of severe weather on Saturday. (NOAA/SPC) Areas at risk: The greatest chance for severe weather on Saturday will be across the Southern Plains. Much of Texas, including Abilene, Waco, Austin and San Antonio, is under an enhanced risk of severe weather — Level 3 out of 5. Elsewhere, a slight risk, corresponding to a Level 2 out of 5 threat, encompasses Houston, Dallas and Oklahoma City. Hazards: Large to very large hail, some to lime-size, will accompany rotating supercell thunderstorms forming between the Texas Panhandle and Hill Country. Those storms will move east, possibly with a continued threat of large hail and damaging winds. A tornado can’t be ruled out, especially where any new thunderstorms in Central Texas interact with boundaries left behind by Friday’s storms. It’s also worth noting that hail could potentially impact some of the larger population centers like Dallas-Fort Worth, which could cause costly damage. Timeline: Storms will develop in west Central Texas by early afternoon, moving northeast toward the Red River Valley and potentially merging into a larger complex of thunderstorms by this evening. Meanwhile, a band of stronger thunderstorms may form near the Interstate-10 corridor in south Central Texas and track northeast before sunset. Those storms should swing east as a broken line that could impact western Louisiana or even extreme southern Arkansas in the wee hours of Sunday morning. Sunday
The amount of spin at the mid levels of the atmosphere, known as vorticity, highlights the disturbance responsible for sparking Sunday’s severe weather threat. This is an American GFS model simulation. (Pivotal Weather) Areas at risk: Much of the Deep South is in play for what could be a higher-end severe weather event, with numerous instances of damaging winds and tornadoes, a few of which could be strong, long-track tornadoes, possible. The greatest concern is focused on the Storm Prediction Center’s moderate risk zone, which encapsulates a swath of southeastern Arkansas, northeastern Louisiana, Mississippi and western Alabama. Birmingham and Tuscaloosa, Ala., Jackson, Miss. and Monroe, La. are included in the moderate risk area. Elsewhere, a large enhanced risk (Level 3 out of 5) covers Little Rock, Memphis, Nashville, and Atlanta. Areas to the east are under a slight risk (Level 2 out of 5), where gusty thunderstorms could arrive by early Monday morning. Hazards: A wide range of severe thunderstorm-related hazards are likely on Sunday, including damaging winds, large hail and the potential for tornadoes. A couple of these tornadoes could be long-track and intense. The threat for strong tornadoes is dependent on the formation of discrete supercell thunderstorms (as opposed to a group of storms forming a squall line, for example) that can fully tap into the moist, unstable air and abundant wind shear. Whether that occurs may not become clear until Sunday morning. Elsewhere, damaging winds and large hail are anticipated, with the risk of flash flooding in Tennessee and across the southern Appalachians. Timeline: Leftover strong to severe thunderstorms from Texas will be ongoing across northern Louisiana or Mississippi Sunday morning and could form into a band with a mainly wind and hail threat. An isolated tornado isn’t out of the question, but that risk is low. That band of storminess will help mix down cooler air to the surface, which could move the highest risk of afternoon tornadic thunderstorms farther south. If supercell thunderstorms form, they would most likely do so in Louisiana and move into Mississippi and Alabama later in the afternoon with an attendant risk of tornadoes, a few of which could be strong and/or long track twisters, along with threats for damaging winds and hail. Late in the evening, storms probably will combine into a squall line known as a “quasi-linear convective system,” or QLCS, with scattered damaging winds and some erratic, quick-hitting tornadoes. That line will move through Alabama and potentially into western Georgia.

Uncertainty: While at least scattered instances of damaging winds and hail are a surefire bet, the magnitude of the tornado risk is considerably uncertain even a day in advance. The atmosphere is locked and loaded, but the types of storms that will form is a big question.

What that means is that, though the ingredients are present for strong, long-track tornadoes, it’s unclear how those ingredients will come together. It’s like how the same ingredients in your kitchen can be combined and prepared differently to make lots of different recipes.

If storms evolve into clusters or squall lines, then straight-line winds will become the primary hazard. If storms are undercut by earlier cold air and become elevated, or rooted in warmer air aloft, then hail could become a more significant threat.

Moreover, a layer of warm air aloft called a “capping inversion” could keep some thunderstorm growth at bay, at least initially on Sunday. As such, it’s uncertain how many supercell thunderstorms will form.

Regardless of how things materialize, at least some risk for tornadoes is expected. However, many ingredients must combine to produce a higher-end, strong tornado threat. Those ingredients all will be present, but the extent to which they overlap remains to be seen.

Monday
The Storm Prediction Center has issued a slight risk of severe weather (Level 2 out of 5) for Monday. (NOAA/SPC) Areas at risk: The immediate Atlantic coastline from the Delmarva Peninsula and near the District of Columbia through Virginia, the Carolinas, Georgia, and into north central Florida. Those regions are under a slight risk (Level 2 out of 5) for severe weather. That’s as the line of severe thunderstorms from Sunday shifts east. Hazards: Scattered damaging winds and isolated tornadoes. Timeline: The system looks to pass a bit later in the day than originally anticipated, making midmorning into the afternoon hours the window of greatest concern. Overall setup

The severe weather risk stems from the synergy between two weather systems — a low-pressure area ejecting over the Southern Plains, and an energizing upper-level disturbance meeting it from the west. That will result in a surface storm that will shift northeast into the Ohio Valley during the weekend.

Ahead of it, southerly winds will transport a warm, moist air mass from the Gulf of Mexico northward. That will provide ample fuel to support severe thunderstorms and heavy rain.

Meanwhile, the low pressure system is dragging in dry air behind it, the resulting “dryline” acting as a triggering mechanism for storm growth. Strong winds higher in the atmosphere that change direction with height, also known as wind shear, will also foster rotation within storms.

The bottom line
The American GFS model simulates a band of heavy thunderstorms moving across Mississippi and Alabama on Sunday evening. (Pivotal Weather

It’s important always to have a severe weather plan in place. This weekend is no exception.

In the face of the coronavirus outbreak, some municipalities have shuttered their community storm shelters. The American Meteorological Society, however, recommends social distancing concerns stemming from the virus should not prevent you from seeking shelter.

Prioritize the most immediate threat — tornadoes and damaging wind — and implement social distancing concerns only once you have arrived at the shelter. Since some shelters may not be open, ensure ahead of time that your shelter of choice will be available.

TORNADO vs. COVID-19: If you live in a mobile home and go to a community shelter when weather gets bad, you should still go to that shelter if/when the weather gets bad Sunday night!

In this thread – 2 things you should do Saturday to keep you and those around you safe. #alwx pic.twitter.com/aqcjmbGfp3

— Josh Johnson (@JoshWeather) April 11, 2020

Above all, it’s a good idea to have multiple ways to be notified of severe weather warnings. This could include making sure wireless emergency alerts are enabled on your cellphone.




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