Flash flooding, locally severe weather puts 46 million in US on alert

By Alex Sosnowski, AccuWeather senior meteorologist

While the risk of tornadoes will be lower starting on Thursday, locally severe thunderstorms and flooding downpours will threaten lives and property over part of the south-central United States into this weekend.

AccuWeather predicts that 46 million people will lie in the path of the repeated flooding downpours and localized severe weather, which will impact areas from Houston and Dallas to New Orleans, Memphis, Tennessee, and Birmingham, Alabama.

Motorists should expect some roads to become blocked by high water, while episodes of torrential downpours may impair visibility on the highways.

The main storm responsible for a broad area of severe thunderstorms since Tuesday will race across the Great Lakes and into Canada to end this week. Heavy, gusty and locally severe weather will occur in the proximity of that departing storm.

However, a swath of moisture will be left behind to fester and cause trouble from near the Rio Grande River to the lower Mississippi Valley and central Gulf Coast into this weekend.

Thunderstorms are forecast to periodically pulse to severe levels over parts of this swath each day.

During the period from Thursday to Sunday, Thursday’s severe storms are likely to be the most extensive with isolated tornadoes.

While widespread, violent storms are not likely from Friday to Sunday, there will still be a risk of a few isolated tornadoes over land each day, as well as the potential for a couple of waterspouts near the Gulf Coast. A couple of the tornadoes could be obscured by rain.

A few incidents of hail and damaging straight-line wind gusts area also anticipated.

The main threat will stem for torrential downpours or rain that persists for hours in some communities on a daily basis. Either way, rainfall of this sort will trigger urban, small stream and low-lying area flooding.

Flooding rainfall has already plagued parts of the region at risk for more downpours through the weekend. During Tuesday, up to 10 inches of rain fell on Sugarland, Texas, which is a northern suburb of Houston.

Similar rainfall and flooding can occur in other communities in the region, and it is possible that parts of the Houston area may be hit again by flooding rain in the coming days.

Rainfall inundates roads in Spring, Texas. Flooding was reported throughout the Houston area on Tuesday. (Twitter/Regina Crawford)

A general 4-8 inches of rain is forecast to inundate communities from central and eastern Texas to parts of middle Tennessee and Alabama with locally higher amounts.

Counting the rain that fell on part of the region this past Tuesday, an AccuWeather Local StormMax™ of 16 inches can occur through Sunday.

With rainfall concentrating on this zone for days, the risk of river flooding will also increase in the short-term and is likely be a problem for the long-term through May and into June.

Even as the rain pauses early next week, rivers may continue to rise.

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From Saturday to Sunday, a press of dry air will bring an end to the rain and thunderstorms from west to east.

However, while much of Texas and Oklahoma is forecast to dry out on Saturday, it may take until Sunday afternoon for clearing to occur in Arkansas and Louisiana and until Sunday night for the same in Tennessee, Mississippi and Alabama.

A new round of flooding downpours and severe thunderstorms is likely to progress slowly eastward across part of the South Central states next week.

Download the free AccuWeather app to receive flash flooding and severe storm warnings on your mobile device. Keep checking back for updates on AccuWeather.com and stay tuned to the AccuWeather Network on DirecTV, Frontier and Verizon Fios.