(This story has been updated.)

At least 18 people are dead in Mississippi and Georgia after violent thunderstorms, some spawning tornadoes, tore across the South on Saturday and Sunday.

Another round of destructive thunderstorms are raking across the Southeast into Sunday evening, and the National Weather Service has declared parts of northern Florida and southern Georgia at “high risk” of severe weather, which is extremely unusual for this time of year.

The Weather Service issued three  “particularly dangerous situation” tornado watches through Sunday evening, reserved for the most serious circumstances when strong, long-track tornadoes are possible:

  • The first watch covered northern Florida and a large part of Georgia. Atlanta, hosting the NFC Championship game between the Falcons and the Green Bay Packers at the Georgia Dome at 3:05 p.m. eastern, was included in the watch.
  • The second watch covered eastern Georgia and southern South Carolina, including Charleston, Savannah, and Augusta.
  • The third watch covered central Florida, including Tampa, Orlando, and Sarasota

Several tornado warnings were issued Sunday afternoon, meaning twisters were imminent or about to occur. Shortly thereafter, an apparent tornado tracked just south of Albany, Ga.

Photos from social media showed damaged and destroyed structures:

The powerful storm system responsible for the violent weather is expected to ride up the East Coast late Sunday into Tuesday, unloading heavy rain and high winds in the Mid-Atlantic and Northeast, with wet snow at high elevations.

In southern Georgia early Sunday, the Associated Press reported, a tornado “ripped through a mobile home park,” killing seven people. Four others died elsewhere in the region.

The day before, four people died when a violent tornado tore through Hattiesburg, Miss., around 3:35 a.m. The storm left behind “massive damage” likely to top $200 million, the AP reported. The responsible twister was rated a 3 on the 0-5 Enhanced Fujita scale, indicating peak wind speeds of 111 to 135 mph.

Since Saturday, the Weather Service Storm Prediction Center logged over 30 tornado reports, 170 reports of damaging winds and 50 instances of large hail across the South.

Dangerous thunderstorms were predicted in the Southeast through Sunday evening. Over 50 million are under an elevated threat of severe weather, according to the Storm Prediction Center. The “high-risk” zone for severe storms includes Jacksonville, Tallahassee, Gainesville and Tampa in Florida and Savannah, Ga.

“This is a highly volatile and dangerous situation!” the Weather Service forecast serving Tallahassee warned in a briefing package.

“You need to take this situation very seriously, like you would a potential hurricane,” the Weather Service office serving Jacksonville said in special statement.

High-risk declarations for severe weather are rare. The last such issuance was June 3, 2014, according to Weather.com and hasn’t occurred in winter since 2008. Since 1984, 42 percent of tornado fatalities have coincided with such high-risk days, according to the Weather Channel’s Kathryn Prociv.

The region under high risk hasn’t seen such a designation in a decade, the website for U.S. Tornadoes reported.

The responsible storm system is unusually strong for winter and much more characteristic of spring. North Little Rock, set a record for its lowest January pressure. The lower the pressure, the more intense the storm. Additional low pressure records could fall in the South, according to Jesse Ferrell, a meteorologist at AccuWeather:

The storm is drawing up a tremendous stream of moisture northward from the Gulf of Mexico. The dew point in Tallahassee, a measure of the moisture in the air, sat at a summerlike 72 degrees early Sunday — about as high as it gets in January.

Very heavy rain is predicted up and down the East Coast, with a widespread one to three inches forecast through Wednesday.

Strong, possibly damaging winds, are predicted for Mid-Atlantic and Northeast coastal areas Monday and Monday night. Gusts of 50-70 mph are possible from the northern Delmarva beaches to eastern New England:

Atlantic City and New York City are included in high-wind warnings in effect from early Monday morning to early Tuesday morning. The Weather Service said the winds could blow down trees and power lines, causing outages.

For ocean areas just off Long Island a hurricane-force wind warning was posted for Monday afternoon and night.

Areas further inland, from Washington to Philadelphia, could experience wind gusts of up to 50 mph Monday.

Minor to moderate coastal flooding is possible from the Delmarva beaches through eastern New England as the strong winds from the east push large waves ashore, especially Monday and Monday night.

Because this storm is drawing so much mild air northward, accumulating snow is likely to be limited to high elevations of the Northeast (Pennsylvania and New York) and interior New England.