Cold snap expected to bring sub-freezing temperatures across U.S.

A large system carrying snow and cold will not make the weather any more pleasant for tens of millions of Americans.

The cold snap many Americans are feeling has its origins from a far-off land, Eric Fisher, chief meteorologist at CBS Boston, reports.

"This one has it's sources way back in Siberia, one of the coldest places you can find in the Northern Hemisphere," Fisher said.

The cold air crosses the pole and heads right on down to Canada and the United States. The real heart of the frigid pocket is coming down Tuesday and Wednesday, when temperatures will dip 20 to 40 degrees below average again, deep down into the Southeast, and record lows will be threatened like we've seen over the past week, Fisher explained.

By Tuesday morning, temperatures will be in the single digits in places like Indianapolis, Des Moines, Iowa., and Fargo, N.D.

In between the cities you'll find some sub-zero numbers and then on Wednesday deeper down into the South, low 20s in Atlanta, sub-freezing temperatures into the Florida panhandle and more record lows certainly in the cards.

The cold air is all being ushered in by snow Sunday night and Monday morning, across Indiana, Northern Kentucky, Ohio and Western New York. Lake-effect snow will start to move in, but it's not just the cold and snow.

Additionally, there is tornado watch across southern Louisiana for tonight and that severe threat will move along the Gulf Coast into tomorrow.

The Florida panhandle, southern Georgia in particular, can expect the possibility isolated tornadoes and damaging wind gusts.

It looks like by next week there will be a little break in the two weeks of cold we've been experiencing for a huge part of the East, just in time for Thanksgiving holiday.