BISMARCK, N.D. — Harsh cold descended on the nation’s midsection Monday as a polar vortex gripped the Rockies and Northern Plains on the heels of weekend storms that pummeled the Eastern U.S. with floods, killing at least 13 people.

The National Weather Service warned of “life-threatening cold” as wind chills dropped to minus-60 degrees in parts of North Dakota on Monday and minus-50 degrees in parts of Montana. Tuesday morning was forecast to be even colder.

Extreme cold warnings were issued for an 11-state swath of the U.S. stretching from the Canadian border to Oklahoma and central Texas, where the Arctic front was expected to bring near-record cold temperatures and wind chills in the single digits by midweek.

Meteorologists had predicted that parts of the U.S. would experience the 10th and coldest polar vortex event this season. Weather forces in the Arctic are pushing chilly air that usually stays near the North Pole into the U.S. and Europe.

Kentucky, Appalachia battered by flooding with at least 13 dead

The death toll in flood-battered Kentucky rose to 11, Gov. Andy Beshear said Monday. Nine of the deaths were flood-related. Two fatal vehicle crashes were connected to the severe weather, he said, and at least 1,000 people stranded by floods had to be rescued.

Parts of Kentucky and Tennessee received up to 6 inches of rain as severe storms swept across the South. Water submerged cars and buildings in Kentucky and mudslides blocked roads in Virginia.

In West Virginia, where there was one confirmed fatality with several people still missing, Gov. Patrick Morrisey said Monday that he has asked President Donald Trump to issue a disaster declaration for a 13-county region ravaged by flooding.

In Atlanta, a person was killed when a large tree fell on a home early Sunday.

Flood warnings were extended Monday across most of Kentucky and portions of Arkansas, Tennessee, Mississippi, Alabama, West Virginia, Virginia and Ohio.

In Nebraska, where much of the state was under a winter weather advisory, a state trooper was killed Monday morning while responding to a crash on Interstate 80 near the town of Greenwood. The trooper’s name and further circumstances of the fatality were not immediately released.

Ice and snow made travel treacherous in large swaths of Michigan, which remained under a winter weather advisory until Monday afternoon.

Parts of a Detroit neighborhood were submerged after a nearly century-old water main burst Monday, flooding streets, sidewalks and yards under several feet of water. The 54-inch transmission main was built in 1930, according to the Great Lakes Water Authority. Crews were attempting to isolate the break. It was not clear what caused it, but overnight temperatures had been well below freezing. No injuries have been reported. Mayor Mike Duggan says people impacted by the flooding can shelter in place if they have power and feel safe.