ROANOKE, Va. – The Polar Vortex has been making its annual rounds on social media again. You’ve likely heard of it before, but what is it? It’s really a normal, cyclical feature in our atmosphere that got attention during an Arctic air outbreak in January of 2014.
It’s not a storm. It’s not made up, and there’s not just one. It’s also not something that hits you.
Rather, pieces of it can break off or split and cause bitter cold in parts of the U.S. and other mid-latitude countries.
There are two Polar Vortices. In order to understand these, you have to think of our atmosphere like a cake. Cakes have layers. Starting from the bottom, you have the troposphere. Then, there’s the stratosphere, the mesosphere and the thermosphere.
One polar vortex is in the troposphere, which the part of the Earth’s atmosphere where humans live. This layer extends all the way up to cruising altitude for jet aircraft. This is typically the vortex that impacts us most.
The center of the vortex resides over the coldest air on Earth and stays there.
However, when the overall weather pattern is more wavy than “usual,” a piece of the vortex can break off and drift into the United States. This results in extreme cold dropping south.
The other vortex is in the stratosphere, which is the layer of atmosphere that starts about 6 miles above our heads. This vortex develops in the fall and winter due to the lack of solar heating in the poles. Studies show this is often disturbed by episodes of warmth in the stratosphere.
This sudden stratospheric warming episode causes the vortex to weaken, allowing Arctic air to spill into parts of the United States. There’s evidence of this warming happening right now (January 7, 2021), which could mean an episode of Arctic chill in another 10-14 days.
How to track this
The Arctic oscillation (AO) keeps tabs on this vortex by tracking the variation of pressure and wind in the atmosphere.
There is a positive and negative phase to the AO.
When the AO goes negative, Arctic-air outbreaks are more likely in this part of the world.
Below is a computer forecast of the Arctic Oscillation through the next few weeks. You can see that most forecast data keeps the AO in its negative phase into the second half of the month.
Cold air will likely be locked into parts of the Continental U.S. due to this negative phase of the AO. There are also indications of high pressure near the West Coast of the United States. This would reinforce cold air and keep storm systems developing on a southern track.
All of this nerdy talk is to say that the rest of January could be active at times.
It’s impossible to predict individual storms weeks out, but the pattern is favorable for at least a little wintry mischief.
Then again, January is when we get about one-third of our annual snowfall. Not all that surprising, if you ask us!