I have been so curious over the past few days to find out who heard the phrase "polar vortex" and decided to thrust it into the mainstream media. When I first heard this term in our WUSA9 newsroom, I was very surprised! To be honest, I had barely come across the term since college, up until this week. You see, the polar vortex is nothing new. Meteorology students learn about it because it is one of the basic, large-scale circulations in the upper atmosphere.
I have heard and read the comparison of a polar vortex to a hurricane, but I want you to know that these two weather phenomena have virtually nothing in common! The only similarity between the polar vortex and a hurricane is that both have strong winds. Hurricanes contain warm, moist air, and they have a center of low pressure. They form over huge bodies of water, usually in tropical locations. Hurricanes can be several hundred miles in diameter. A polar vortex, however, is made of extremely cold, dry, and dense air. It's not connected to any storm system or center of low pressure; instead, it can best be visualized as a pinwheel, somewhat circular in shape but with undulating edges. It rotates around one of the poles; the Northern Hemisphere's polar vortex is located at the North Pole. It exists in the upper atmosphere, miles above the surface. You cannot see it the same way you can see a thunderstorm or a snowflake.
The polar vortex is present in the Arctic Circle year-round, and is not unique or unusual. It has literally been there since the atmosphere started circulating. It gets stronger in the winter, as the sun angle gets lower and the Arctic air gets colder. The Polar Jet Stream usually does a good enough job of bottling up the coldest air, keeping it out of the DC Metro area, but this cold and dense air can bend the jet at its weak spots, creating a trough of Arctic air like we have in place right now.
Another fact that I've heard tossed around is that climate change could make these polar outbreaks more common in our area. Finally, I get to say that this one is probably true! As temperatures in the Arctic have gotten warmer, the polar jet can weaken because the jet's winds are driven by the strength of the temperature difference between the poles and the Equator. If the temperature difference isn't as great, then the jet won't be as strong. As I mentioned before, a weaker jet is not as strong a barrier for those Arctic winds, making it more likely that they will spill down into our area. Many climate scientists believe that climate change will lead to more weather extremes, and it is possible that this is another extreme that we'll have to deal with!
That said, I just want to point out that this cold weather is extreme, but not really historic. We did set 2 new record lows at Dulles and BWI airports this morning, but the old record lows were "sitting duck" records of 8 degrees, set in 1988. And our high temperatures were not as "impressive"; we did not set any new records for a coldest high temperature in our area.
Take heart, DC... the cold snap is almost over! :-)