The most shocking images of the destruction by the winter storm in the US 1:35
(CNN) --
A sprawling storm threatens to deliver a triple whammy of heavy snow and strong winds combined with freezing temperatures across much of the US on Wednesday, lasting through the end of a busy week of travel.
Forecasters have been warning this week's powerful storm could bring travel to a standstill as it affects areas of the Northwest across the Plains, the Great Lakes and central Appalachians before reaching the Northeast later in the week, according to the National Weather Service.
Winter weather alerts are in effect for more than 70 million people from Washington state to Maryland.
The heaviest snow is expected to fall in the Cascades and across northern Idaho, northwestern Montana and western Wyoming, where more than 12 inches are forecast, according to the weather service.
Polar air and a powerful winter storm put 50 million people on alert this holiday week in the United States
For many other northern parts of the country, even if less snow falls, it is expected to be light and fluffy, and when blown by 30 to 50 mph winds, it could make travel dangerous for the next two to three days.
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Along with the wind, the brutally low temperatures have prompted wind chill alerts that stretch from the Gulf of Mexico to the US-Canada border and from the Pacific Northwest to the Southeast.
The wind chill, which indicates how the wind feels, could be between 10 and 20 degrees Celsius below zero, according to the weather service.
"The wind chill of this magnitude can cause frostbite in less than 5 minutes if precautions are not taken, hypothermia also being possible due to prolonged exposure to cold," the weather service warned Tuesday.
Throughout this Wednesday, the storm system will cross Montana, Idaho and Oregon in the morning.
It will start affecting cities like Minneapolis, Omaha, Denver and Salt Lake City in the early afternoon and continue into the evening.
In anticipation of what could be a nightmare week for travelers, United, American, Delta, Southwest and Jet Blue have issued travel waivers for dozens of airports across the country, from the South to the Northeast, because in addition to the With snow covering the roads, low visibility could make air travel dangerous.
"With such a large and powerful storm system affecting most of the nation during one of the busiest travel weeks of the year, it is imperative that travelers check the latest forecast before venturing out," the weather service advised.
In response to the colossal storm, the governors of various states across the country have taken some preparedness measures.
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Colorado Governor Jared Polis has activated more than 100 National Guard members to support extreme cold weather operations across the state, according to a news release.
"Colorado is about to face extreme weather conditions and low temperatures, and the Guard is prepared to help local communities keep people safe during this snap of extreme cold," Polis said.
North Carolina declared a state of emergency on Tuesday to help with the transportation of fuel and critical supplies, as well as help first responders and protect consumers from rising prices, the governor's office said in a statement.
West Virginia has been declared in a state of preparedness, according to the governor.
Missouri has also activated the state's emergency operations plan, which frees up National Guard resources to respond to the storm's impact if necessary.
A "bomb cyclone" in development
So far, snow has fallen mainly in parts of northern and central Montana, northern and central Idaho, eastern Oregon, western North Dakota, central South Dakota, and western Colorado.
The storm, which is expected to become a bomb cyclone, is forecast to strengthen rapidly as temperatures drop sharply across most of the US later in the week.
For a storm to be defined as a bomb cyclonic, it must drop 24 millibars (a measure of atmospheric pressure) in 24 hours.
These storms are more typical of winter nor'easters.
But in this week's case, the bomb cyclone is expected to occur on the Plains, where there is an extreme temperature difference between the warm, moist air preceding the storm and the arctic air mass moving from Canada behind. her.
The storm is expected to reach pressure equivalent to a Category 2 hurricane upon reaching the Great Lakes, with the weather service describing the force of the downpour as a "once-in-a-generation" event.
"This is a case where snow totals may not tell the whole story. Even small amounts of snow, when combined with very strong gusts of wind and plummeting temperatures, can cause poor visibility and slippery areas on roads. The sudden arrival of these conditions can increase the danger," explains the weather service.
In addition, strong winds can bring down power lines from the Midwest to the Northeast, especially in areas where heavy snow fell last week and is already weighing down tree limbs.
CNN's Sharif Paget, Devon Sayers, Amanda Musa, Leslie Perrot, Pete Muntean and Robert Shackelford contributed to this report.
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