The Weather Service’s National Storm Prediction Center highlighted a level 3-of-5 “increased” risk of severe weather from southeastern Louisiana to the Florida Panhandle on Tuesday. Nearly 4.5 million Americans fall within this zone, including residents of New Orleans; Baton Rouge; Gulfport, Mississippi; and Mobile, Ala.
On the cold side of the storm system, moderate snowfall is expected. Winter Storm Alerts and Alerts, as well as Winter Weather Alerts, span from eastern New Mexico to western Ohio. Up to 8 inches of snow is likely to come out of the storm, which is expected to fall on the Great Lakes late Wednesday.
The weather so far this month has been unusually active as far as heavy thunderstorms go, but comparatively quiet in the eastern United States for winter weather. Since the beginning of January, the Storm Prediction Center has recorded 138 reports of tornadoes, compared with a monthly average of about three dozen.
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The persistently mild climate in the east, although favorable for heavy storms, proved to be detrimental to snowfall. New York, Philadelphia, Baltimore and DC have yet to record any measurable snowfall, and Boston sits at a mere 4.3 inches – compared to an average of over 20 inches at this point in the season.
The storms are expected to hit central and northern Texas and perhaps Oklahoma by Tuesday morning. These should be raised or rooted in rising hot air and over a shallow lip of cool. As a result, they are unlikely to produce a tornado threat early on.
Coastward along a warm corridor, a storm line with damaging direct winds and incorporated tornado circulations is likely to form. There may also be some isolated rotating supercell storms ahead.
The storms are forecast to pass through Houston and Galveston, Texas during the early afternoon, reach the Golden Triangle of southeast Texas and southwest Louisiana in the evening, and likely make landfall in New Orleans around midnight. There is a minimal chance of a strong isolated tornado from New Orleans towards Mobile.
On Monday morning, a low pressure system was spread across Las Vegas. It is expected to dip southeast over Chihuahua and Coahuila, Mexico before crossing south Texas near Brownsville and then working northeast through Tuesday.
Downtown will pass through northern Louisiana on its way to the Mississippi Valley. As the minima rotate counterclockwise in the Northern Hemisphere, this means that the winds ahead of the system will come from the south. This will draw a warm, humid air mass north from the Gulf of Mexico – but it could only get as far as 100 miles north of the actual coast. How far north it travels will determine the northerly extent of the tornado risk.
At the same time, a drop in jet stream should be sweeping overhead with a robust change in wind speed and/or direction with height. Surface winds should flow from the south – then southwest at mid-levels and south-south-east at high. This “wind shear” will facilitate the rotation of any storm spanning multiple layers of the atmosphere.
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At the rear of the system, cold air moving south is expected to turn precipitation to snow in parts of North Texas, Oklahoma, Northwest Arkansas, Southeast Missouri, Southern Illinois, Central Indiana, West of Ohio and southern Michigan.
The snow band will be narrow, but in the center of the band decent accumulations are expected. In southern areas, most people can expect 3 to 6 inches, with 4 to 8 in the most impacted parts of the Midwest.
The wind shouldn’t be a problem. Several large metropolitan areas, such as St. Louis; Fort Smith, Ark.; Indianapolis; and Dayton, Ohio are included in the winter storm warnings.
The snow is expected to arrive in Sooner State by Tuesday morning and will last about 18 hours in most places.
The precipitation is expected to start as rain in northwestern Arkansas on Tuesday night, turning into heavy, wet snow as the atmosphere cools. West Tennessee could see some snow on Tuesday night, and Illinois, Indiana and Ohio will likely wake up to snow on their doorsteps on Wednesday morning.
By Wednesday through Thursday, snow will likely make its way inland from the Northeast, with rain forecast mostly along the East Coast.
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