What's causing freezing temperatures across the U.S.?

Why has this winter been so tough? 01:33

WASHINGTON -- With temperatures in the teens in Washington D.C., the C&O Canal is frozen solid. So are tens of millions of people from Maine to the Carolinas.

"And now to add insult to injury there's been some of the coldest air in the last couple of decades invading the Northeast from the Arctic," says Dave Robinson, a professor of climatology at Rutgers University.

Niagara Falls almost freezes over 00:18

He says what's behind it all is the polar vortex.

"The polar vortex is essentially the coldest air found in the Northern Hemisphere, and it's situated up in the Arctic in the bulk of the winter," Robinson says. "But occasionally, a lobe of that will dip south above the jet stream and allow that cold air down into the Middle Atlantic states. Sometimes last winter, it was into the northern Plains."

But while the polar vortex has pushed that mass of cold air south in the eastern part of the country, it's moved in the opposite direction out west -- bringing warm, dry weather.

"We really have a snow drought out west," Robinson says. "We won't have that water available for irrigation and drinking water out West as we go into next summer."

Robinson says the worst could be yet to come, in the form of flooding if the New England ice pack melts too quickly.

  • Chip-Reid_bio_140x100_bw.jpg
    Chip Reid

    Chip Reid is CBS News' national correspondent.