On Tuesday, the National Weather Service’s Storm Prediction Center highlighted a severe weather risk from southeastern Louisiana to the Florida Panhandle as “enhanced” at a Category 3 out of 5. Nearly 4.5 million Americans live in the area, including residents of New Orleans; Baton Rouge; Gulfport, Mississippi; and Mobile, Alabama.
Moderate snowfall is expected on the colder end of the storm system. Winter storm watches and warnings, and winter weather advisories, from eastern New Mexico to western Ohio. The fast-moving storm, which could bring up to 8 inches of snow, should slide into the Great Lakes late Wednesday.
So far this month, the weather has been exceptionally active with severe thunderstorms, but winter weather in the eastern United States has been relatively calm. The Storm Prediction Center has recorded 138 tornado reports since January began, out of an average of about three dozen per month.
Continued mild weather in the east, while favorable for severe thunderstorms, is proving to be detrimental to snowfall. New York, Philadelphia, Baltimore and the District of Columbia have yet to record any measurable snowfall, while Boston has seen a paltry 4.3 inches, compared to an average of more than 20 inches for this time of season.
Thunderstorms are expected to hit central and northern Texas and possibly Oklahoma Tuesday morning. Those should be elevated, or rooted in the warm air, rising and over the shallow cold edge. Therefore, they are unlikely to generate a large tornado threat early on.
Heading toward the coastline in a warm corridor, a train of thunderstorms could develop with damaging straight-line winds and an embedded tornado-like circulation. There may also be some isolated rotating supercell thunderstorms ahead of it.
The storm is expected to hit Houston and Galveston, Texas in the early afternoon and reach the Golden Triangle in southeastern Texas and southwestern Louisiana by early evening and possibly New Orleans around midnight . The chances of an isolated strong tornado from New Orleans to Mobile are slim.
A low-pressure system spread across Las Vegas Monday morning. It should swoop southeast over the Mexican states of Chihuahua and Coahuila, then cross south Texas near Brownsville before moving northeast into Tuesday.
The depression will then pass over northern Louisiana and move up the Mississippi Valley. Since the low pressure rotates counterclockwise in the northern hemisphere, that means the winds ahead of the system will be from the south. That would draw warm, moist Gulf of Mexico air northward — but it would likely only be about 100 miles north of the actual coastline. How far north it travels will determine the northern extent of the tornado risk.
At the same time, dips in rapids should sweep overhead, with wind speed and/or direction changing drastically with altitude. Surface winds should be blowing in from the south – then mid-level southwest, then south-southeast aloft. This “wind shear” will make it easy to spin any thunderstorms that span multiple layers of the atmosphere.
On the backside of the system, a southward wrap of cold air is expected to move northern Texas, Oklahoma, northwestern Arkansas, southeastern Missouri, southern Illinois, central Indiana, western Ohio, and Precipitation turned to snow in parts of southern Michigan.
The snow belt will be narrow, but in the center of the snow belt, a decent amount of snow is expected. In the South, most people expect 3 to 6 inches, with 4 to 8 inches in the hardest-hit Midwest.
Wind is not expected to be a problem. Several major metro areas, such as St. Louis; Fort Smith, Arkansas; Indianapolis, Indianapolis; and Dayton, Ohio, are on the winter storm watch list.
Snow is expected to arrive in the Sooner State Tuesday morning, lasting about 18 hours in most areas.
Rain should start in northwest Arkansas Tuesday night, turning into big, wet snow as the atmosphere cools. Light snow is possible in western Tennessee Tuesday night, and snow could be on their doorstep Wednesday morning in Illinois, Indiana and Ohio.
Snow could reach the interior of the Northeast by Wednesday through Thursday, with rain expected across much of the East Coast.