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Weekend weather expected to be treacherous for much of the U.S.

"As a cold arctic air mass remains in place across much of the country, wintry precipitation" is expected from coast to coast, National Weather Service says.

Winter is blasting through the country, with extreme weather forecast on both coasts while much of the middle of the country deals with bitterly cold temperatures.

Large swaths of the U.S. are being warned about weekend conditions. Nearly 90 million people were under winter weather alerts or worse.

"As a cold arctic air mass remains in place across much of the country, wintry precipitation will bring hazards to the Pacific Northwest, the Southern Plains, Mississippi Valley into the Ohio Valley, and the Mid-Atlantic to Northeast this weekend into at least early next week. Temperatures will remain 20 to 40 degrees below normal across the center of the country on Saturday," the National Weather Service said Friday night.

Governors in Oklahoma, Texas and Louisiana have declared emergencies in their states ahead of a storm that is expected to bring heavy snow, ice and rain.

The National Weather Service was warning of bitterly cold temperatures and near-blizzard conditions in the Dallas-Fort Worth area, where six people were killed in Thursday in a 130-care pileup on an icy interstate.

Forecasts were calling for up to 6 inches of snow and windchills 15 degrees below freezing.

In Harris County, Texas, which includes Houston, officials urged residents to be prepared for icy roads and up to inches of snow through the weekend and beyond. "Wherever you are Sunday night, you should be prepared to stay there through at least Tuesday," county officials said.

A polar plunge that has gripped much of the Midwest for days on Friday is expected to linger for much of next week.

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In Kansas City, Missouri, the high was 8 degrees Friday, and forecasters warned it will dip as low as -20, with wind-chill factored in, over the weekend.

The intensifying cold wave throughout the Southern Plains is so dangerous that the National Weather Service office in Pleasant Hill, Missouri warned residents to be aware of the signs of hypothermia and frost bite.

"If you have warming shelters that you need to make plans for now is the time to prepare them," the office said in situation report on the bitter cold.

"A quasi-stationary front at the leading edge of the cold air mass will remain over the Southeast through Sunday evening," the weather service said in a forecast discussion Friday.

The Pacific Northwest started seeing more snow and some freezing rain Friday afternoon after snow fell in parts of Washington and Oregon on Thursday.

The weather service issued an ice storm warning Friday for Oregon’s Central Willamette Valley including Salem and for the southern Portland metro and a winter storm warning for the Portland/Vancouver, Washington areas. After 5 p.m. freezing rain had started to fall in places around the Portland metro area, the Multnomah County Sheriff’s Office said.

Forecasters said the Portland area could see up to 8 inches of snow and the Cascades could get another foot through Saturday.

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A winter storm warning is also in effect for the greater Seattle area where 2 to 8 inches of snow was expected along with winds gusting to 40 mph. A winter storm warning for the Olympia, Washington area predicted up to another foot of snow into Saturday after that city received more than 6 inches in some places on Thursday.

The weekend would also bring severe winter weather to the Mid-Atlantic, where an ice storm was expected.

The Washington, D.C., area was under an advisory, and Baltimore residents are bracing for an ice storm, with power outages and tree damage likely.

"Travel could be nearly impossible" Saturday night into Sunday morning, the National Weather Service warned.