Very cold December, temperatures are seven degrees below average

By Ros Runner - bio | email
Posted by Terry Alexander - email

RICHMOND, VA (WWBT) – We are now half-way through December and temperatures are running more than seven degrees below average.

So what happened?

The key is in the jet stream. The jet stream is a zone of fast moving winds 20-30 thousand feet up in the atmosphere. These winds help direct the movement of cold and warm air masses around the globe.

Underneath a ridge in the flow of the jet stream, you typically find warmer air at this time of year.

Underneath a dip or trough, you'll find cold or even arctic air masses. This month, we have seen a persistent trough located over the eastern half of the United States allowing for repeated shots of cold, arctic air to spill in our direction.

At the same time, a ridge located over the continent of Greenland known as the Greenland block, has kept this trough locked in place and prevented any significant breaks in the relentless cold pattern. So will this pattern persist through the winter?

The answer is, very likely not. You may have heard us talk about the fact that La Nina is active this year which often results in a jet stream pattern that produces an overall warmer and drier than average winter in the southeastern United States, including Virginia.

The bitter cold is destined to break, and perhaps in dramatic fashion.

So it's not so much a question of if, but when. It won't happen right away though as the pattern continues to look very cold through the Christmas holiday and perhaps even through the start of the New Year, and we'll probably throw in some snow to go along with it. 

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