Extreme cold in the US arose from changes in the Jet Stream, which forms a container for the Polar Vortex. The darker purple below shows the coldest temperature. The break up of coldest air above the North Pole illustrates Climate Destabilization in action.
Maps show the 500-millibar geopotential height (the altitude where the air pressure is 500 millibars) on January 5, 2014 (left), and in mid-November 2013 (right). The cold air of the polar vortex is purple.
The polar vortex is a high altitude low-pressure system that hovers over the Arctic in winter. When the polar vortex is strong, it acts like a spinning bowl balanced on the top of the North Pole. The image on the right shows a strong phase of the polar vortex in mid-November 2013. Dark purple depicts the most frigid air tightly contained in an oval-shaped formation inside the invisible bowl. The light purple line forming the outermost boundary of the cold Arctic air is the jet stream in its normal west-to-east pattern.
In early January, the polar vortex weakened ... allowing fragments of cold air to slosh out of the bowl into mid-latitudes. The image on the left shows the weakened vortex formation on January 5, 2014. The high pressure building up in the Arctic slowed down the jet stream, which caused it to buckle into deep folds and flow farther south than usual, introducing cold Arctic air into the central and eastern U.S.
In recent years, climate scientists have noticed that the jet stream has taken on a more wavy shape instead of the more typical oval around the North Pole, leading to outbreaks of colder weather down in the mid-latitudes and milder temperatures in the Arctic, a so-called “warm Arctic-cold continents” pattern.
As I've said before on other posts of yours, I'm not "liking" the fact, but I do like and appreciate that you're sharing it, especially with such a concise, vivid graphic!
Our weather is nuts. No snow; most of it melted by rain. Some bitter cold winds desiccate trees, shrubs and soils. Forecasts for coming week are highs between 41 and 48 degrees F; lows of 28 to 38 degrees.