(CNN) - Huge swaths of the South, Midwest and East Coast are under the gun for severe weather as states still recovering from last weekend's tornadoes hunker down for more.
On Thursday, "the greatest threat for tornadoes will be along the Gulf Coast states of Mississippi and Alabama," CNN meteorologist Michael Guy said.
The National Weather Service said Thursday afternoon that a large and damaging tornado had been observed in southern Mississippi.
The massive storm system won't leave the South quietly, either. It'll fan out to the Ohio Valley region and then the East Coast, threatening 100 million people with severe weather Thursday and Friday.
"Severe thunderstorms may produce damaging gusts, a few tornadoes (possibly strong), and isolated large hail today across the lower Mississippi Valley through the central Gulf Coast region," the National Weather Service's Storm Prediction Center said.
In Louisiana, the forecast is so dire that New Orleans City Hall and other local government offices were to close early Thursday, the mayor's office said. New Orleans was being pounded by the storm during the afternoon.
"Showers and thunderstorms continue through most of our area and heading eastward," the weather service office in New Orleans tweeted just after 4 p.m. "Severe weather is still possible."
A weather station in Ethel, Louisiana, reported almost 3 inches of rain for a six-hour period Thursday.
Where are these storms headed?
This storm system will barrel toward the East Coast through Friday, unleashing tornadoes, damaging winds and hail from the Texas Panhandle to the coast of the Carolinas.
By early Friday morning, it will move through Georgia, then through other coastal Atlantic states.
Dangerous conditions will ramp up throughout the day Friday along the East Coast, spreading from the southern tip of Florida to all the way to Washington, DC.
Who's at the greatest risk Friday?
The coastal parts of the Carolinas and southeastern Virginia have the greatest potential Friday for severe weather. That area is at "enhanced risk," the Storm Prediction Center said, referring to the third level of severity on a scale of five.
Damaging winds and tornadoes could strike the Southeast and mid-Atlantic states, especially within the "enhanced risk" area.
The threat should diminish throughout the overnight hours into Saturday as the cold front linked to the storms finally pushes off shore.
CNN's Taylor Ward, Steve Almasy, Allie Mazurek and Keith Allen contributed to this report.
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