Winter storm: Tornadoes, flooding rain threaten East Coast

At least three people were killed and multiple others injured across four states amid severe weather on Tuesday as a major storm system threatens parts of the East Coast.

More than a dozen tornadoes have been reported from Texas to Georgia since Monday, many occurring overnight and Tuesday morning in Florida's Panhandle, as the major storm crossed the country.

A tornado hit the Panama City area in Bay County early Tuesday, according to the National Weather Service.

At least five people in the county were transported to hospitals with injuries, Bay County spokesperson Valerie Sale told ABC News. There are also reports of significant damage throughout the county due to the storm, Sale said.

Florida Gov. Ron DeSantis has issued a state of emergency for northern Florida due to the severe weather threat. The order covers 49 counties in north and central Florida.

Vice President Kamala Harris' was aboard Air Force Two when it was forced to reroute to Dulles International Airport after leaving Atlanta, due to "inclement weather."

"Tonight, en route from Atlanta, GA, Air Force 2 was diverted from Joint Base Andrews to Dulles International Airport due to inclement weather," Harris' press secretary Kirsten Allen said in a statement.

A source familiar with the situation told ABC News Air Force Two encountered wind shear.

In Georgia, one person is dead after a tree fell on a vehicle while the driver was traveling on Highway 54 in Jonesboro Tuesday morning, police said.

In North Carolina, one person was killed and four others injured at a mobile home park in Claremont following severe weather, Catawba County officials said. The National Weather Service is determining if a tornado occurred.

An 81-year-old woman in Cottonwood, Alabama, was killed Tuesday morning after a possible tornado blew her mobile home over several times while she was inside, according to the Houston County Coroner's Office.

Tornado watches remain in effect along a large swath of the East Coast, from Florida into southern Virginia. The threat of strong, damaging wind gusts and tornadoes from severe thunderstorms will persist through the afternoon and into the early evening hours.

As of Tuesday evening, more than 600,000 customers in the South, Mid-Atlantic and Midwest were without power, including more than 200,000 in the Carolinas.

Flood threat in the Northeast

The storm system is expected to swing north and bring flooding and damaging winds to the Northeast later Tuesday.

Flood watches are in effect along a large swath of the East Coast, including Washington, D.C., Philadelphia, New York City and Boston.

Heavy rain is expected to gradually move up the Interstate 95 corridor through the afternoon and evening to Philadelphia and New York City, with a chance of flooding possible.

The worst impacts from this powerful storm are forecast to begin to unfold in parts of the Northeast by early Tuesday evening, first hitting the D.C./Baltimore area around 6 p.m. ET. with heavy rain and strong wind gusts sweeping in.

In the greater New York City metro area, the worst impacts are expected roughly between 8 p.m. and 2 a.m. ET, with extremely heavy rain and very strong wind gusts.

Additionally, New England is predicting heavy rain on Tuesday night into Wednesday with possible flooding. An estimated 2 to 4 inches of rain is forecast in the Northeast on top of all the melting snow.

Strong damaging winds are expected to accompany the heavy rain as, locally, 50 to 65 mph gusts are possible from the Virginia coast all the way up to Maine. Power outages are possible in swathes of the Northeast.

On the back side of this storm, heavy snow is forecast from Missouri to Iowa and into Wisconsin and Michigan where, locally, up to 10 inches of snow could be possible.

Chicago will be right on the line of rain and snow with only a few inches of sloppy snow possible in the city and up to 5 to 10 inches west and north of the city.

Nearly 1,150 flights have been canceled and more than 7,000 delayed on Tuesday amid the storm, as well as the ongoing 737 Max 9 issue. Chicago's O'Hare International Airport, Ronald Reagan Washington National Airport in Arlington, Virginia, Newark Liberty International Airport in New Jersey and LaGuardia Airport in NYC were among the most impacted.

2nd storm moving into the West

A second storm is also moving into the Pacific Northwest and the northern Rockies with more heavy snow, strong winds and heavy rain for the coast.

A rare blizzard warning is in place for Oregon and Washington, just outside of Seattle and Portland, where some areas have not seen a blizzard warning issued in more than 10 years.

The storm will follow in the current storm's footsteps and will bring more severe weather to the South with tornado and flood threats Friday and more heavy snow for the Midwest and the Great Lakes.

By Friday night into Saturday, the storm will move into the Northeast with more heavy rain, strong winds and flooding.

ABC News' Alexandra Faul and Daniel Amarante contributed to this report.