A storm system more reminiscent of spring than the dead of winter will besiege the South with severe thunderstorms and torrential flooding rain Friday and Saturday. The Arklatex and the Gulf Coast are expected to face the brunt of the severe weather, where violent straight-line winds, large hail, and dozens of tornadoes are expected.
The upper-air energy responsible for the violent weather originated in the Pacific Ocean and only approached the northern California coast Thursday morning with scattered rain and snow showers. That nuisance area of precipitation will undergo a rapid transformation as the supporting area of upper-level energy intensifies over California and the Desert Southwest through Thursday night. The precipitation will largely dissipate but the supporting upper-level system will nonetheless deepen into a highly amplified trough. New area of low pressure will develop over Texas early Friday with the approach of this vigorous Pacific system.
The rain will begin Thursday night over the Arklatex as the jet stream begins to draw on moisture from the Gulf of Mexico. The intensifying jet stream will help push a subtropical air mass across the country’s midsection overnight, allowing showers and thunderstorms to spread throughout the mid-Mississippi Valley by Friday morning.
Conditions will gradually worsen throughout the day Friday as low pressure develops over northern Texas. The low pressure will be fed by a rapidly intensifying flow of Gulf of Mexico moisture colliding with an arctic air mass over the Southern Plains. An explosion of thunderstorms in the vicinity of this low pressure system will ensue.
Thunderstorms will bombard parts of the South-Central US for nearly 24 consecutive hours spread between two phases. The first phase will emerge as discrete thunderstorms across the Arklatex Friday morning and afternoon. These storms will initially pop up over southeastern Oklahoma and northeastern Texas late in the morning. Surface heating into the mid 70s and rising dew points into the upper 60s will provide ample fuel for these storms. Increasing lift from the Pacific trough will serve as the ignition. Extremely strong wind shear associated with the trough will allow the storms to develop rotating updrafts and become supercelluar.
These supercells Friday afternoon and evening will be capable of producing golf ball-sized hail, damaging wind gusts, and a few strong and long-lasting tornadoes. Large metropolitan areas including Dallas, Houston, and Austin are at risk for these dangerous storms, as are smaller cities across Louisiana and southern Arkansas including Shreveport and Lafayette.
The second, more widespread phase of severe weather, is expected to manifest during the evening ahead of the developing low’s cold front. Thunderstorms will quickly coagulate into a slow-moving squall line during the evening and overnight hours over eastern Texas and Oklahoma. The line will expand throughout the night, extending from the Louisiana Gulf Coast to St. Louis by 6am Saturday. The line of storms will have the capacity to produce embedded tornadoes and hurricane-force wind gusts of up to 80 mph.
Flash Flooding and River Flooding are expected to be widespread as torrential rain falls for hours at a time. The most persistent rain will fall near the low’s path, with 3-5″ of rain falling over the Arklatex region and up to 4″ of rain falling across Missouri and Illinois. Major rivers at risk for flooding include the Red, Arkansas, Missouri, and Mississippi.
The squall line will not waiver Saturday as it marches eastward across the Gulf Coast. Eastern Louisiana, Mississippi, Alabama, and the Florida panhandle will be encapsulated in the same soupy air mass behind Friday’s severe weather, offering abundant fuel to sustain the approaching line of storms. A few discrete supercells could develop ahead of this line but the powerful straight-line winds and embedded tornadoes from the squall line will be the primary threat for the Gulf Coast. As low pressure intensifies over the Mississippi Valley the forward momentum of the storms will increase, sparing the Gulf Coast from the flash flood threat of the Arklatex. Nonetheless the damaging winds will be strong enough to knock-out power and produce structural damage to cities all across the South, including New Orleans, Jackson, Birmingham, Pensacola, and Atlanta.
The severe weather threat will finally dwindle after 7pm CST with the loss of daytime heating and forcing from the Great Lakes-bound upper-level trough. The storms will leave a trail of structural damage, downed trees and power-lines, and flooded homes and businesses in their wake.