Mount Washington Observatory with temperatures out of this world.

After an unseasonably warm January across the eastern half of the lower 48, some of the coldest air of the season will pour into the Northeast on Friday through Saturday.

This week the polar vortex has weakened and will allow frigid air to escape the Arctic and move southward across North America.
"A ferocious Arctic blast will bring dangerous cold and blowing snow Friday into Saturday," tweeted the National Weather Service in Maine, as it forecasted bone-chilling weather, with "wind chills in the 50s below across the north."

Upstate New York meteorologist Ben Frechette tweeted, "the coldest airmass on the entire planet will be over New England by Friday night – the only comparable air currently exists over central Siberia."