Destructive storms are sweeping the South, producing tornadoes and flooding

The Weather Service also confirmed that an EF2 tornado hit Lake Charles, La., early Wednesday.

Midmorning Wednesday, a damaging tornado hit areas near Slidell, La. and caused numerous injuries. A tornado may have also struck the Stennis Space Center in southwest Mississippi, just east of Slidell, where the Weather Service received reports of damage to cars by a thrown container.

The Weather Service reported four people were injured in St. Landry Parish, La. — about 20 miles north of Lafayette — when a tree fell on a car.

Flooding was an escalating problem Wednesday. The Weather Service issued a flash flood emergency for New Orleans late in the morning, its most dire flood alert; it was allowed to expire at 2 p.m. Central time when downpours eased. “Emergency management reported numerous roads in and around New Orleans are underwater and impassible,” the Weather Service wrote. “This is a PARTICULARLY DANGEROUS SITUATION. SEEK HIGHER GROUND NOW!”

The Weather Service received reports of roads and underpasses closed because of high water. More than half a foot of rain fell in New Orleans, its second-highest April calendar day total on record. In addition to torrential rain, winds gusted up to 70 mph around the city.

Flash flood warnings affected parts of Louisiana, Mississippi, southern Alabama and a sliver of East Texas at times Wednesday; the Weather Service had also issued a flash flood emergency for portions of Tyler, Jasper and Newton counties in southeast Texas. Radar estimated over 18 inches of rain southwest of Newton, near the Louisiana border.

In Yazoo County, Miss., the sheriff’s office warned that a levee was in danger of breaking in the Eastbrook subdivision on Highway 16 and was working to evacuate threatened homes.

Heavy rain and an ocean surge flooded portions of Interstate 10 near Mobile on Wednesday afternoon, stranding vehicles.

Wednesday’s severe storm risk was advertised as a Level 4 out of 5 by the Weather Service’s Storm Prediction Center in the area from Mobile to Pensacola, Fla. Tornado watches in effect from southern Louisiana to southwest Alabama had been allowed to expire but a watch remained in effect in southeast Alabama, southwest Georgia and parts of the Florida Panhandle until 8 p.m. Central time.

The Weather Service was predicting “numerous” severe thunderstorms through the day, with the potential for “several tornadoes, a few of which may be strong, and widespread damaging winds.”

By the time the system reaches the East Coast on Thursday, the risk will become more scattered.

Severe storm activity is expected to pause this weekend, but a renewed batch of dangerous weather, with the potential for a “substantial” severe weather event, will come Monday over the Plains.

Severe thunderstorm risk Wednesday

Strong to severe thunderstorms swept through southern Louisiana on Wednesday morning. One had prompted a “destructive” severe thunderstorm warning for areas around Baton Rouge. Gusts of 70 to 80 mph were expected, prompting the Weather Service to warn of hurricane-force winds.

By late afternoon, the storms were barreling through Florida’s Panhandle.

With strong jet stream winds roaring overhead, it will be easy for storms to mix momentum to the surface in the form of destructive straight-line winds as storms sweep eastward.

The tornado threat is a bit more uncertain. Within the squall line, small areas of rotation may produce brief tornadoes, but any lone, isolated cells ahead of the mainline will pose a greater threat of stronger tornadoes.

The greatest concern will lie at the northern edge of the warm, moist air mass wafting north out of the Gulf of Mexico. It’s along that warm front that a zone of increased low-level helicity, or spin, could boost the chance of an isolated strong tornado.

Severe thunderstorms will continue marching east before fading overnight.

Flooding concerns

The severe storms were embedded within a broader mass of rain and downpours spreading northeast. It’s likely that some areas will see eight to 12 hours of off-and-on downpours. The heaviest cells will produce rainfall rates of 1 to 3 inches per hour. That’s why some places have seen, and will see, 6 inches or more of rain.

A conveyor belt of moisture from the Gulf of Mexico is providing continuous fuel for storms, particularly in the areas between southeast Louisiana and southern Alabama.

The flood risk will be greatest along a stationary front, along which storms will train, or move repeatedly over the same areas.

“Flash flooding is likely across the region, and areas of considerable to high-impact flash flooding are expected locally and especially where the greatest areas of cell-training occurs,” the Weather Service wrote. “This includes a notable threat to the I-10 corridor and the urban corridors along it.”

Instances of flooding will become fewer and farther between into Georgia on Wednesday evening.

The storm risk Thursday and beyond

On Thursday, two zones of thunderstorms are expected — one in the Ohio Valley beneath the core of the high-altitude cold air, low pressure and spin at the center of low pressure, and one along the trailing cold front in the Southeast.

Both zones could yield an isolated tornado, in addition to some damaging wind gusts of 55 to 60 mph.

Across the Mid-Atlantic between both zones, only a Level 1 out of 5 marginal risk is in place. That’s where more widely scattered storm cells could produce gusty winds.

Behind the cold front, a cooler air mass will reduce severe weather odds across North America for the weekend, but more storms are likely Monday over the southern Plains. The Storm Prediction Center has taken the uncommon step of drawing a Level 3 out of 5 enhanced risk for severe weather more than five days in advance for Oklahoma, and notes that significant severe weather is expected.