- Central Tennessee and North and Central Alabama, including Nashville and Birmingham, through 1:00 a.m. Central Time.
- Southeast Mississippi, South Alabama, and West Florida Panhandle, through 4:00 p.m. Central Time.
At 8:51 p.m. Central Time, the National Weather Service Storm Prediction Center published a special He noted that a “significant tornado threat is emerging” in far southeastern Mississippi and southwestern Alabama. Areas near McClain, Miss. appeared to be hit by a tornado based on storm chaser reports. Toomsuba, Miss., was also struck by a vortex; the national weather service had issued a tornado warning for the city for particularly dangerous situations, Warning of a confirmed large and dangerous tornado.
About 120,000 customers were without power in Louisiana, Mississippi, Alabama and Tennessee primarily due to strong winds. The Weather Service had received 138 reports of damaging winds and 14 reports of tornadoes. Many of the reports came from downed trees and power lines, but some pointed to damage to homes and buildings.
The storms, blowing east at 30 to 50 miles per hour, were focused on southern Mississippi and western and central Alabama on Wednesday night. Damaging storms and tornadoes remain a possibility until midnight before activity weakens slightly overnight as it shifts further east.
Late Wednesday afternoon, the Weather Service warned of a confirmed tornado near Jackson, Miss., when radar spotted debris blowing up. Social media footage showed damage across the city.
More severe thunderstorms are possible along the east coast Thursday, and there are signs that April is favored for showing above-average thunderstorm and tornado activity in the Lower 48.
“Review your severe weather safety procedures today for the possibility of hazardous weather,” urged the Storm Prediction Center in a public severe weather forecast released early Wednesday.
Even outside of the destructive thunderstorm line expected to form, ambient winds ahead of storms can blow in excess of 50 mph.
“Harmful winds will blow down trees and power lines,” wrote the National Weather Service in Mobile, Alabama. “Widespread power outages are expected.”
All of Mississippi, Alabama, Louisiana, Tennessee and Kentucky are covered by wind alerts and strong wind alerts — alerts that also cover a broader swath of the South and Ohio Valley.
Amid the dry, windy air ahead of the storm system and in its wake, there is one increased risk of fast-moving fires Wednesday in parts of the Tennessee Valley as well as in Texas, where several such blazes erupted on Tuesday.
The Level 4 of 5 red zone includes all of Mississippi, western Alabama, eastern Louisiana, and southwest Tennessee.
Memphis; Tupelo, Starkville, Hattiesburg, Meridian and Jackson, Miss.; Tuscaloosa, Mobile and Montgomery, Alabama; and Monroe and Alexandria, La., are in the highest risk category. A lower but still significant increased risk of level 3 out of 5 covers Nashville, Little Rock, New Orleans, Birmingham and Huntsville, Alabama.
It’s unclear how far east the line will remain intact before fragmenting and weakening late Wednesday or early Thursday.
Storms developing Wednesday morning had taken the form of a QLCS, or quasi-linear convection system, as they entered midday Louisiana. This is essentially a thunderstorm line with embedded rotational kinks, any of which could become tornadic.
Given the setup, a few things are worth noting:
- Thunderstorms will move very fast through the deep south. This may limit the advance notice of hazardous weather.
- With strong jet stream winds in the air, it will be easy for thunderstorms to bring momentum to the surface. That means widespread winds of 60 to 80 miles per hour within thunderstorms.
- Even barring thunderstorms, winds can blow up to 50 mph ahead of the storm line and then over 22 mph in the wake of the storms when the winds turn from the northwest.
- There is enough wind shear to support isolated, fast-forming, short and irregular tornadoes along the QLCS. Due to the fast forward movement of the leash, it wouldn’t take much for a pair of EF2+ to do damage. There may also be some embedded rotating thunderstorms or supercells in southern portions of the line over southern Mississippi, the Louisiana Delta, or southern Alabama.
Thunderstorms will hurtle east at speeds in excess of 80 km/h. Current forecasts indicate that:
- Storms hit Tuscaloosa at 9 p.m. and Birmingham about an hour later.
- Thunderstorms hit Nashville around 9 p.m
- Mobile, Alabama could see storms around 9 or 10 p.m., after which the storms continued in the Florida Panhandle.
Thunderstorms will move so fast that they don’t “know” they’ve escaped the conditions that fueled them until long after they’ve made their way east. That means they probably won’t fade much until they near the Georgia border around midnight.
Danger of storms on the east coast on Thursday
Severe storms are possible from New York State to Florida on Thursday. The zone of greatest risk for severe weather, rated Level 2 of 5, includes the mid-Atlantic from Richmond to Scranton, Pa., including the Washington-Baltimore region and northern Florida to southern South Carolina.
“Damaging wind gusts and hail are the main threats, but low-level vertical shear is strong enough to support a tornado or two,” the Storm Prediction Center wrote.
The setup for the storm Wednesday
Daylight dawned on severe thunderstorms over the Ozarks in southwestern Missouri, western Arkansas and far southeastern Oklahoma, and northeastern Texas just east of Interstate 35. These storms erupted along a dry line, or leading edge of dry air, late Tuesday desert from the southwest. This dry line ran south from a low-pressure system over the Corn Belt, powered by an approaching disturbance in the upper air.
The same surface low-pressure zone will intensify the south-southeast winds ahead of the front, pulling a mild and moisture-rich air mass north from the Gulf of Mexico and draping it over the south. However, the cloud cover left over from Tuesday’s storms will curb daytime warming, meaning the air mass will not be “juiced” as much as it might otherwise.
Despite the comparatively modest fuel for severe thunderstorms, shear, or a change in wind speed/direction with altitude, is extreme. That’s thanks to a roaring low-altitude jet stream, or a river of fast-moving air, pouring north into the surface about a mile above the ground. This means that all clouds that get high enough will have a tendency to rotate.