The German ICON model simulates heavy rain across the South and the Southeast through late Thursday. (WeatherBell)

Super Tuesday’s weather is shaping up to be stormy for millions of potential Democratic presidential primary voters across the Deep South, where strong to severe thunderstorms and heavy rainfall will douse an already waterlogged region. It’s part of a continued wet pattern that has been going on for most of the winter across a large swath of the southern United States. Up to half a foot of rain is possible in many areas by late this week, with more wet weather possible thereafter.

Five Super Tuesday states are anticipated to see rough weather at the time that polls are open. Weather can play a significant role in elections by inhibiting voter turnout, particularly when severe conditions are anticipated that cause changes in public transit, for example.

The threat of severe weather will start in Texas on Tuesday and shift east each day this week, riding along the Interstate 20 corridor as the storminess makes its way to the Southeast. In recent computer model runs, the cold front initiating the severe weather has slowed down, tempering severe weather chances while boosting the flood potential.

The anticipated deluge over the lower Mississippi and Tennessee river valleys comes after what was one of the top five wettest meteorological winters for many cities. Some places are approaching three times the rainfall they should typically have for this date.

The severe weather risk

The European model simulates lightning activity overnight Tuesday night into Wednesday. (WeatherBell)
  • Voters in Alabama, Arkansas, Tennessee and Texas are all slated to vote in the Democratic primary on Tuesday, and each of these states is in the severe weather risk zone that day.
  • Most of Texas should see showers and a few thunderstorms throughout the day Tuesday. The risk of strong to severe thunderstorms — including threats of large hail, gusty winds and tornadoes — will ramp up by late in the day in the western part of the state, including places such as Midland and Odessa, and overnight into early Wednesday elsewhere. Storms may not roll into the major population centers of Dallas, Houston and Austin until late Tuesday evening and early Wednesday, based on current forecasts. Polls close at 7 p.m. Central time.
  • In Alabama, rainy weather will spread across the state early Tuesday morning, with heavier downpours and thunder in places such as Montgomery, Birmingham and Auburn, between sunrise and noon. Polls close at 7 p.m. Central time.
  • Arkansas will largely dodge the severe weather until Wednesday morning, although a few thunderstorms could occur early in the day in eastern sections near the Mississippi River, including West Memphis and Jonesboro. Polls close at 7:30 p.m. Central time.
  • Tennessee could awaken to a few strong storms, especially in western and central areas, very early Tuesday morning. These could be hail-producing storms in particular. Rain showers should continue throughout the day. Polls close at 7 p.m. Central time.

Severe thunderstorms will first erupt over Texas on Tuesday, eventually extending into Louisiana and southwestern Mississippi by nightfall. Places such as Austin, San Antonio and Waco could get a few strong storms, earlier in the day farther west and later to the east.

Northern locations run the risk of hail with their storms, while southern regions face more of a locally damaging wind threat.

Storms could rumble across southern Louisiana and Mississippi well after dark and into Wednesday morning.

By Wednesday, the cold front triggering the severe weather will sag south toward the Gulf Coast, shifting the greatest risk of severe weather into far southern regions of Louisiana to adjacent coastal Mississippi and Alabama, and perhaps even the Florida Panhandle.

It’s uncertain how much warm, humid and unstable air will move north over land Wednesday, but if there is a northward shift of warm and humid air, then the stage could be set for a few supercells — or rotating — thunderstorms.

If that occurs, a slight tornado risk would present itself. Farther north, a few severe storms would be possible into the rest of Louisiana, southern and central Mississippi and adjacent southwestern Alabama on Wednesday.

Heavy rain threat

The American GFS model simulates heavy rain stalling along a frontal boundary late Tuesday. (WeatherBell)

Of the Super Tuesday states, Texas and Alabama are most at risk of flooding Tuesday.

At that point, a wave of low pressure will form east of the mountains in Mexico. It will be re-energized by an approaching dip in the jet stream moving east across the western United States. That will help the low to consolidate and intensify some as it treks across South Texas and along the Gulf Coast.

Ahead of the low, a plume of exceptionally moisture-rich air will ride north and overspread coastal areas over Louisiana, Mississippi and Alabama. Atmospheric water vapor content will approach daily record values over those areas.

A cold front to the north will help focus heavy rainfall, bringing about a flood potential as well. Areas beneath this stalled front could wind up in the jackpot zone, where four to six inches may fall.

In an indication of this flood threat, the Weather Prediction Center has shown slight risks of excessive rainfall Tuesday and Wednesday.

On Tuesday, heavy rain will coincide with the severe weather risk in west and Central Texas, but a second area to watch will manifest itself in southern Alabama and possibly west Georgia. These places will experience a sneaky threat from “training,” or repeated rounds of precipitation. Tennessee, which could receive a touch of wet weather, too, and Alabama are both states that will vote on Super Tuesday.

By Wednesday, the Interstate 10 and 20 stretches of Mississippi, Alabama and Georgia are likely to be affected.

“Much of this area has received over 200% of normal precipitation over the past couple weeks,” forecasters wrote in an online discussion.