Areas of low pressure rotate counter-clockwise, dragging air around them in such a pattern. When all things are equal, in the Northern Hemisphere, warm air rises from the south on the eastern flank of a low, and cold air sinks south on the western flank. There are some undulations, notably with topography and the presence of large bodies of water that modify this scenario in some locations, but more or less, that is how it works.

The most nefarious of our weather comes as the cold air tries to intersect with that warm air, all while the atmosphere is trying to rotate. There are updrafts caused by the cold digging in, latent buoyancy of the warmer air, and the twistiness of the wind pattern. This can mean rain, thunderstorms or even heavy snow. This is why the northern Plains can get wicked blizzards, and the Southern Plains and increasingly the lower Mississippi Valley are prone to strong thunderstorms and tornadoes.

We’ve already seen a busy start to February, with severe weather afflicting the Lower Mississippi Valley, and copious snows falling from Kansas to Iowa, though the southern Great Lakes. Temperatures, as you might imagine, have been fairly warm in the eastern US, with an unusual chill out west. Before these past few days, the cold was aided in part by Pacific systems coming ashore, bringing clouds and rain. Now, it’s simply a colder air mass.

Knowing that it is the clash in air mass that fuels stronger weather, and particularly when the clash is between western cold and southeastern warmth, the long term out look suggests action to come.

Whether in response to persistent lee troughing in the High Plains, or a result of a static jet pattern, this temperature trend for the end of the month and beginning of March indicates some busy times, both for tornado chasers centered in the middle of the country, and snow plows in the Upper Mississippi Valley.

In the Upper Midwest, the story of the winter has been the snow. Several rounds of accumulating snow have buffeted the Twin Cities, but temperatures have always rebounded, because the responsible storms are bringing moisture from the Gulf, rather than cold air from the north. That is changing with a series of Clippers that moved through last weekend.

Temperatures in Minnesota ahead of the cool down were in the 30s and seasonably pleasant, but they are going downhill, and the low temperatures will reach all the way to Chicago and the western Great Lakes by Tuesday morning. This was the forecast for Tuesday morning in the Upper Midwest.

That cold has stuck around, and while it was chilly Tuesday, a reinforcing shot of the cold air came this morning, and it was as cold as -35 in International Falls, Minnesota. Unlike the initial rounds, this cold air is pressing further east, and while the Twin Cities and Minnesota are warming this weekend, it’s going to be dangerously cold in New England.

And unlike the cold in the Upper Midwest, there is a deep area of low pressure northeast of the Canadian Maritimes, bringing a brisk northeast wind, not only reinforcing the cold air, but introducing significant wind chill. Boston could see a wind chill of -30 in the early hours.

Great news, though. While this cold, the coldest shot of the winter in a lot of places, and in parts of New England the coldest in a decade, is brutal, it’s reign is at an end. Next week is forecast to be much warmer than normal for many locations in the chill this week.

It is the beginning of the year, and already we have had our first notable severe weather outbreak. With the strong storms pounding the west, it was only a matter of time before the cold air wrought havoc when making contact with the more sultry air east of the Rockies.

Tornadoes left a path of damage in Alabama and Georgia over the weekend, including a tornado that led to the deaths of at least 6 west of Montgomery. The strong areas of low pressure have drawn unstable air as north as Iowa, where the first January tornado was reported there since 1986. Now, a strong storm is expected to leave a foot of snow in the northern High Plains.

It will be the tornado that struck Selma, Alabama that will be remembered the most out of this town, striking a town so closely associated with the Civil Rights Movement on the weekend that celebrates one its greatest champions, Dr. Martin Luther King, Jr. The tornado went through the heart of the city, just north of the down town area and the Edmund Pettus Bridge, damaging homes, churches and businesses throughout the city. StormChasingVideo provides a look at the city and nearby Autauga in the aftermath of the tornado.

As long as cold air resides in the west, feeding into much warmer air east of the Rockies, there will be a threat that storm systems could amplify quickly and dangerously. The snow storm in the Dakotas and Nebraska today will ultimately lead to an additional threat for severe weather in the Mississippi Valley later the is week. The long term outlook, for a cold wet west indicates an active winter in the south as well.