Warm Stratosphere = Cold?
While it may seem counterintuitive that warming up a layer of the high atmosphere can cause the reverse to happen on the ground, a warm up in the stratosphere can bring very cold temperatures to many areas, especially with the stratosphere goes through a warming process over the Polar regions.
How could this be? Using the analogy of a musical instrument, an accordion is a good way to understand the phenomenon.
During the winter, especially in the months of December, January and February, there can be periods of time when the high layers of the atmosphere (60,000 feet and higher) go through warm phases. Since warmer air takes up more volume than colder air and wants to expand (think hot air balloon), the higher layers of the stratosphere expand vertically (both up and down). The movement up, vertically is restricted somewhat by the top of the atmosphere near the edge of space. Therefore, the vertical push is stronger downward (toward the ground).
The vertical push down forces cold air near the North Pole/Arctic Circle to be pushed the south. Sometimes these pushes of cold air can go far south into the United States but other parts of the globe as well (Europe, Asia, Siberia).
Long range computer modeling is suggesting that the stratosphere could go through a warming phase beginning Christmas week and into the New Year. Confidence is growing that this will happen and if it does, beef producers should be prepared for what could be the coldest temperatures of the season during the last week of December and into the first week of the New Year.
Historically, the coldest air usually extends from the Rockies to the Midwest before expanding the East Coast.