There is no rest for the weary in the storm-ravaged South-Central US. Severe thunderstorms will resurge across portions of Texas and the Deep South later this week, where just two days ago a severe weather outbreak spawned 34 tornadoes and took at least 8 lives. All modes of severe weather including damaging wind gusts, large hail, and destructive tornadoes are possible Wednesday and Thursday.
The active Pacific jet stream will again be the precursor to this week’s outbreak. A low pressure system will douse the Pacific Northwest Monday and Tuesday with heavy rain as its upper-level component dives southeastward across the Rocky Mountains and Desert Southwest. A reinvigorated low-pressure system will emerge from the Rockies into the southern Plains Wednesday and feed on the contrast between the warm, humid, and unstable Gulf of Mexico air mass engulfing over the Central US and the cool, dry air mass spreading over the northern Plains and the Northwest. Contributing to the pandemonium will be a sweeping dry desert air mass trekking south of the cold air mass but west of the Gulf air mass. The collision of these three very different air masses will trigger a violent uprising of severe thunderstorms.
Thunderstorms will first erupt early Wednesday afternoon in New Mexico, the Texas panhandle, western Oklahoma, and southwestern Kansas ahead of the intensifying low’s trailing cold front. Instability and wind shear will generally be meager here, so these storms are not expected to produce severe weather besides a few isolated damaging wind gusts near the border of the Texas and Oklahoma panhandles. Areas further east will not be as fortunate.
East of the Texas and Oklahoma panhandles Wednesday, the thunderstorms will have a relatively late start. Dry air aloft flowing from the Rocky Mountains will keep a lid on convection until late afternoon when the sun and ascent from the approaching jet stream initiate convection strong enough to break the lid in eastern Texas, eastern Oklahoma, and southwestern Arkansas. The penetration of the convective cap will be like removing the lid from a pot of boiling water. The building instability alongside increasing shear will cause thunderstorms to shoot upwards and rapidly develop rotating updrafts. These supercell thunderstorms will pose a primary threat of damaging wind gusts and large hail with diameters greater than that of golf-balls with a slight chance of spawning tornadoes. As the evening wears on the supercells will cluster together across the Arklatex, by which point damaging wind gusts will have become the primary threat.
While scattered supercells cluster in the Arklatex, the cold front will encounter increasingly unstable air. The front’s passage will trigger the development of intense clusters of thunderstorms across northern Texas, central Oklahoma, southeastern Kansas, and southwestern Missouri Wednesday evening. These storms will quickly organize into a linear structure. Winds strong enough to blow over roofs and knock down trees and power-lines will be the primary threat with these storms, although large hail and weak tornadoes will also be possible before the storms organize.
Long after dark Wednesday, the dry-line separating the dry desert air mass from the swampy Gulf air mass will cut across Texas. The dryline will generate thunderstorms, which will organize into a squall line whose main threat is damaging wind gusts over central Texas. The storms will reach peak intensity near the heavily populated I-35 corridor between the late evening and early overnight hours. Residents of cities like Dallas and Austin may find themselves awoken by frequent claps of thunder if the sudden blast of wind ahead of the storms doesn’t wake them first.
The cold front will eventually overtake the dry-line overnight in eastern Texas. The combined air mass will be greater than the sum of its parts and help trigger new thunderstorms. Those who had endured rounds of thunderstorms Wednesday afternoon and evening in the Arklatex may be surprised to be awoken by yet another round of severe weather. The severe weather will spread to southeastern Kansas, Missouri, and southern Illinois, remarkably in the overnight hours without the help of daytime heating. Damaging wind gusts will be the primary threat with these storms.
The soupy air mass and vigorous jet stream will allow the storms to survive the night. The storms will have organized into a single but disjointed squall line of thunderstorms stretching from central Illinois to western Louisiana by day break Thursday. The low pressure system behind Wednesday’s severe storms will drag the cold front southeastward Thursday, shifting the cross-hairs of severe weather to the Southeast. The squall line will start in a disheveled state Thursday morning, but will gradually intensify with daytime heating and as the cold front catches up to it. It will be capable of producing severe weather, namely in the form of damaging wind gusts, by the time it reaches the Mississippi River early afternoon, threatening the Tennessee Valley, the southern Ohio Valley, Mississippi, Alabama, and Georgia with tree-toppling wind gusts. The squall line will maintain its severe characteristics through the overnight hours, when it will impact the Atlanta metro area.
The line of thunderstorms is expected to survive yet another night into Friday morning. It may again be reinvigorated Friday over the East Coast, where flash flooding will be an additional concern to damaging winds. This is expected to be a long-lasting severe weather event spanning at least two-days. Those in the Central and Southern US in the severe risk area are urged to pay close attention to the forecasts in the coming days. As always, we will provide further updates leading up to the expected severe weather.