The Gulf States, Southeast U.S. And East Coast Severe Weather Episode April 12-13

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Gulf States/Southeast/East Severe Weather Episode April 12-13

Fig. 1-4: NOAA/SPC severe weather outlook for Sunday and Monday including tornado risk areas and annotated timing of primary squall line.

Severe weather discussion: Tornado watch areas are posted in central Texas to northern Louisiana for the onset of an area of squalls featuring high risk of severe thunderstorms, excessive rainfall, hail and tornadoes. The area of squalls shifts to Louisiana midday, Mississippi into early evening, across Alabama and into Tennessee late evening and along or just east of the Appalachian Spine at 8AM EDT Monday. The greatest tornado risk today is from Louisiana (away from the coast) late morning/midday to the northern half of Alabama tonight. Today’s severe weather outbreak is forecast to affect 15 states with tornadoes affecting 7 states. The event is unusually large and intense and is likely to feature widespread destructive wind, damaging hail bursts and long path/duration tornado episodes (Fig. 1-2). The severe weather re-ignites just-ahead of a cold front on the East Coast tomorrow morning/midday (Fig. 3). Tornado risk is present from the Carolinas to Virginia (Fig. 4). The event clears the East Coast by early afternoon while lingering (but weakening) crossing southern New England during the afternoon.

Fig. 5-6: NOAA/WPC excessive rainfall/flash flood risk areas for today and tomorrow.

Excessive rainfall forecast: The greatest risk of flooding due to excessive rainfall occurs late day and especially at night from the Interior Southeast U.S./Tennessee Valley to southern Appalachia (Fig. 5). Forecast models indicate potential for 2-6 in. of rain. The night-time flash flood risk coupled with tornado presence indicates a life-threatening event spread over a large area. Risk of excessive rain and flash flooding remains although less intense for the coastal Northeast Corridor on Monday (Fig. 6).

High wind forecast: While a large tornado outbreak coupled with flash flooding rainfall much of which occurs tonight is the primary focus of the immense developing storm there is also a large swath of damaging wind produced by this storm (Fig. 7). The primary concern area is the Mid-Atlantic Coast to New York and New England tomorrow where southerly wind ahead of the squall line could gust to 55-65 mph causing widespread power outages and damage to many structures. The peak risk is midday/early afternoon tomorrow. Wind gusts to 55 mph are forecast tomorrow afternoon across Michigan and the Ohio Valley. High wind with heavy snow should cause blizzard warnings tomorrow in the Upper Midwest. Wind advisories for wind gusts from 35-45 mph are posted from the Corn Belt into the Southeast U.S. which are easily exceeded when severe weather moves through. The tornado event is underway in East Texas. High wind propels afternoon temperatures to 100F in southern Texas today. Winter storm warnings for a late season heavy snowstorm is posted for the North-central U.S.

Fig. 7: Current NOAA/NWS extensive array of weather watch, warning and advisories valid today and tomorrow.