A winter storm that has hit a large swath of the United States has killed several people and caused thousands of flights to be canceled or delayed due to the weather.

The storm caused chaos over the weekend from Texas to the tip of Maine, snarling roads, knocking out power and leaving major cities buried under deep snow.

At least a dozen people have died in multiple U.S. states. More than 20 inches (50.8 centimeters) of snow fell in parts of the Northeast in the past 24 hours, according to the National Weather Service (NWS), and Canadian officials said the storm was severely disrupting southern Ontario.

Forecasters warn that another “severe winter storm” could hit the eastern United States again this weekend.

As of Monday afternoon, more than 200,000 people were without power in Tennessee. The city experienced a deep freeze, plunging residents into cold and darkness.

“There’s a lot of trees down, power lines blocking the roads,” Joy Flores, vice president of homeless shelters at the Nashville Rescue Mission, told the BBC. Her center is fielding calls from residents without power.

Flores said the roads were icy and impassable and her home had “no heat, no internet and no coffee.”

Eight people died in New York City as temperatures plunged into single digits from Friday into Monday morning, according to city officials.

According to the National Weather Service, 11.4 inches of snow had fallen in New York City’s Central Park as of Monday morning.

A teenage girl has died and another is in critical condition following a sledding accident in Texas, the Frisco Police Department announced.

In North Carolina, a man was found dead on the side of a highway in Buncombe County, and authorities are investigating whether his death was weather-related. The Louisiana Department of Health said two people have died from hypothermia.

Massachusetts Gov. Maura Healey warned state residents on Monday that “this is not over yet,” with one to five inches of snow expected to fall on Monday.

In Canada, Ottawa and Quebec were hardest hit by the storm, causing traffic problems and multiple school closures.

According to the Canadian Broadcasting Corporation (CBC), Toronto Pearson Airport received 18.1 inches (46 centimeters) of snow on Sunday, setting a new record for the airport.

American Airlines customers continued to experience setbacks and delays on Monday. Airlines experienced more than 19,000 delays and 5,900 flight cancellations on Monday, according to FlightAware.

Relief may not come soon. The “potential is increasing” for another winter storm starting Friday, according to the National Weather Service. Such an event could bring very cold temperatures to the eastern United States and bring “widespread heavy precipitation.”

The U.S. Weather Service warned that forecasters don’t yet know the potential path of the storm or where its impact will be greatest.