Dangerous cold gripped the Midwest and Northeast on Wednesday, and even more snow was on the way for some places.
Winter weather watches were in place across 17 states from Montana to Maine, an area inhabited by 120 million Americans. The storm was carrying gusty winds, and wind-chill forecasts neared minus-50 in northern Minnesota, minus-42 in Fargo, North Dakota, and minus-28 in Chicago.
It will be "ridiculously cold," said Ari Sarsalari, a forecaster for The Weather Channel. He warned that exposed skin can freeze in as little as 15 minutes in those conditions.
Ann Beatty, a letter carrier in Plattsburgh, New York, where wind chills were expected to drop to 25 to 35 degrees below zero, was already planning for her seven hours of work outside.
Beatty gathered "extra socks, gloves, hats, rain gear, an extra pair of boots in case yours get wet," she told NBC station WPTZ. "There's nothing worse than wet feet."
Earlier this week, a winter weather system raced across the country and dropped snow from the Pacific Northwest to the Northeast. Forecasters called for even more through Friday, much of it lake-effect snow.
The Weather Channel said parts of Michigan could get a foot, and a foot and a half could fall through Friday outside Syracuse, New York.
The Buffalo area — where a massive snowstorm led to record flooding that killed 13 people in November — could get as much as 16 inches of new snow, forecasters said.
On Tuesday, almost 250 flights were canceled into and out of Philadelphia International Airport. More than 210 were canceled at Reagan National Airport in Washington, which got 4 inches of snow Tuesday. And 205 were canceled at the three New York-area airports.
By 3 a.m. Wednesday, more than 100 flights were canceled at airports across the nation.
Robert Ericson, a charter pilot and flight instructor for Orchard Beach Aviation in Manistee, Michigan, said it's not just icy runways that pilots have to worry about.
"Cold weather can wreak havoc on any aircraft, big or small," Ericson told NBC station WPBN of Traverse City, Michigan. But on the plus side, he said, "the colder, more dense air really helps an aircraft, so, usually, they can take off with much more weight than they typically would, say, than on a hot day in Denver."
Alexander Smith and Erin McClam of NBC News contributed to this report.