What is a "polar vortex" low?

The bitter cold outbreak had the national media talking about a "polar vortex" system on Monday. If you haven't heard of it before, I don't think you are alone. It is something we studied in meteorology and is not new. This kind of low pressure system is pretty common in the wintertime when the jet stream winds (at roughly 40,000 feet) push farther south, delivering much colder air to the eastern half of the United States. The magnitude of cold air varies with each polar vortex low pressure, and this one just happened to latch on to some of the coldest air some places haven't seen in 20 years. Just looking at the wind chills of 20 and 30 below made you cold.

Typically, when a polar vortex system sets up over the Great Lakes and southern Canada, we have dry weather around Kansas with lake effect snows in the upper Midwest. And it can take a few days to a week for these large systems to break down and move away. This one won't be around for much longer. I think by Wednesday, it will be weakening and heading east. Much of the country should be climbing out of the deep freeze as the week continues.

Almost half way through winter, here is how we stand on snowfall for the season. Most areas are near normal on snow, except in the northwest, where several places are 5-10 inches below average. One good winter storm can wipe that out.