By Ralph Ellis and Holly Yan
Frigid weather gripping much of the United States led to a frenzied search in northwest Nevada, where rescue teams are searching a mountainous area for two adults and four children who went to play in the snow and never returned.
James Glanton, 34, and Christina MacIntee, 25, are missing, along with Glanton's two children and MacIntee's niece and nephew. The children are 3 to 10 years old, the Pershing County Sheriff's Office said.
The group set out Sunday for Seven Troughs mountain range and haven't been seen since.
Fears intensified as the temperature plummeted to below zero.
Amanda Fitzpatrick, mother of 10-year-old Shelby Fitzpatrick, has joined the search in the freezing cold.
"It's been extremely hard, probably the hardest 24 to 36 hours of my life," she told CNN's Piers Morgan. "It's my baby girl."
More snow and ice
The pre-winter wintry weather isn't over yet. Temperatures in storm-stricken parts of the country are expected to stay about 10 to 20 degrees below normal for the rest of the week, the National Weather Service said.
Federal offices in Washington are closed Tuesday as more sleet, snow and freezing rain are expected. And a swath of 2 to 6 inches of snow is expected to fall Tuesday from Virginia to the New England coast, forecasters said.
Philadelphia can expect to get 3 to 5 inches of snow on Tuesday; New York, a little less than that.
The storm will finally leave the East Coast late Tuesday, but the mercury won't rise above freezing until at least Friday, the National Weather Service said.
Elsewhere across the country, Portland, Oregon, and Chicago will see snow and freezing rain this week.
Even St. Louis has been colder than Anchorage, Alaska.
"It's very unusual," CNN meteorologist Dave Hennen said. "This literally spreads across the entire U.S."
Choked off travel
At least the nation's airports are getting back to normal. The website Flightaware.com says about 775 flights have been canceled for Tuesday. That's down from the 1,900 flights canceled Monday and 2,800 Sunday.
But road conditions have been treacherous. At least 15 people have died from weather-related incidents in the past several days, mostly in traffic crashes. Eight died in Oklahoma alone, state officials said.
And the hazardous conditions in northern Nevada have many concerned about the missing children and adults.
"If there's one thing you should learn from the lessons of these people, never let your tank below a half a tank (of gas) in the winter," CNN meteorologist Chad Myers said. "You might need that for the electricity, for the power, for the heat in that car."
CNN's Randi Kaye, Chuck Johnston and Judson Jones contributed to this report.
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