Arctic blast marches eastward, bringing record low temperatures to the northern U.S.

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The upper Midwest is in a deep freeze on Tuesday, with the arctic air expected to shift eastward and affect millions of people as the week wears on.

The National Weather Service posted advisories for the Dakotas and Minnesota on Tuesday, with wind chills from 10 to 20 degrees below zero. Wind chill is the combination of air temperature and wind, and forecasters say wind chills this cold can cause frostbite to exposed skin in as little as 30 minutes.

The cold will affect parts of the northern and eastern U.S. later this week and into the weekend, with frigid temperatures expected in the Great Lakes, Mid-Atlantic and Northeast regions, according to Climate Prediction Center forecaster Stephen Baxter.

Below-normal temperatures are expected this weekend and into Monday across the entire northern half of the country, from the Pacific Northwest to Maine and as far south as Oklahoma, Arkansas and Virginia, according to the Climate Prediction Center.

Up to half a foot of snow also could fall from the Upper Mississippi Valley to the Northeast on Friday and Saturday, and areas east of the Appalachian Mountains could see freezing rain and sleet on Saturday.

The arctic blast has already hit the Northern Plains and will move into the Midwest Tuesday night, before setting its sights on the Northeast on Wednesday. 

In the Midwestern cities of Chicago, Cedar Rapids, Minneapolis and Sioux Falls, temperatures will only get as high as the teens on Wednesday, and will be even more brutal thanks to gusting winds. 

These winds will pick up speed over the Great Lakes, mixing with the cold front to cause lake-effect snow in parks of Wisconsin, Michigan, Pennsylvania, Ohio and New York. 

The lake-effect snow is expected to start on Wednesday, with the the brunt of snowfall expected between Bufffalo, New York and Cleveland, Ohio. The Tug Hull Plateau of Upstate New York could also see as much as 30 inches of snow.   

While the blast moves to the Northeast by the end of the weekend, temperatures will remain very low in the Midwest on Thursday, not going above the single digits in Minneapolis, Madison and Chicago. 

By Friday yet another blast will blow into the States from Canada, starting in the Northern Plains and making the same path Eastward over the weekend.   

Weather conditions will be the worst for the major East Coast cities of New York, Philadelphia and Boston Thursday night going into Friday morning, when temperatures will go no higher than the 20s. 

Road conditions will be especially dangerous in Boston and Hartford, Connecticut Friday morning, with temperatures in the single-digits. 

On the bright side though, the winds accompanying the storm are expected to die down by then.   

Another arctic air mass on the heels of this cold front is expected to bring temperatures to the northern Plains over the weekend and into early next week that will be as much as 24 degrees below normal, according to Baxter.

The West Coast hasn't escaped Old Man Winter's scorn this week either. Starting Wednesday, a winter storm will make it's way into the Pacific Northwest. 

Winter storm warnings are already in effect in parts of Oregon, Northern California, Wyoming and Montana. 

That storm will also move west, sandwiching itself between the two arctic blasts.