WASHINGTON (FOX 5 DC) - Winter officially begins on Friday and already social media is abuzz with reports that the East Coast could see a polar vortex this season.
It's true: We have the potential for a polar vortex but several dots will have to align to make that a possibility.
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Here's what you need to know about the potential for a polar vortex and when it could possibly hit our region:
First: Some Polar Vortex 101
1) What is it? Simply put, it is a naturally occurring and wide area of upper atmospheric low pressure that is typically found sitting over the Arctic regions. Even though it has been a "buzzword" more commonly seen within the last several years, the polar vortex is not a new phenomenon. It is almost always up in the Arctic region somewhere, thanks in no small part to the natural rotation of the earth and the fact that it is a globe. It is even up there during the summer months, although much weaker.
2) It works the opposite as what you may think during the winter months. A strong, healthy polar vortex is actually a warmer signal for us here across the mainland United States because it means all the cold air is locked up over the polar regions. The polar vortex is always at its strongest in these regions.
3) When the polar vortex is weaker as has been the case so far this season, it is more easily perturbed or broken into weaker sections. The onset of these perturbations can be due to any number of features. Strengthening upper-level high-pressure systems, tropical forcing such as El Nino and La Nina, or strong surface storms tracking into the polar region can all upset the balance that is the polar vortex.
4) When the polar vortex is disrupted, pieces of it can break off and travel southward. Contrary to the assumption that it is the polar vortex itself that is overhead during major cold air outbreaks of winter's past, it is instead a "broken piece" of the vortex that is able to travel southward. They don't only impact our area either. They can impact any of the northern latitudes and have brought extreme cold to Europe and Asia just as often as here in the United States.
Could we see a polar vortex this season, and if so, when?
-- There was a large expansion of snowfall across northern Asia during the late fall months and a considerable amount of early season snowpack across the Northern Hemisphere as a whole. Stronger than the past several winters. This is important because the sun's radiation reflected off the large areas of snow returns and hits the stratosphere to a stronger degree than if there was less or no snow present. The ozone present in the atmosphere reacts to this additional radiation, causing a warming effect.
-- Weather models are currently forecasting a sudden surge in stratospheric temperatures over Northern Asia by this weekend. The key, however, is this area of strong high altitude warmth is forecast to advance northward towards the polar region by the Christmas holiday.
-- The strong warming over the pole is of great importance. We call them "SSWs" or "Sudden Stratospheric Warming" events. Warming of this degree heading to the polar region has been linked to initializing the formation of Arctic upper-level regions of high pressure, we call these simply "blocking patterns." It's these blocks that disrupt the polar vortex, often times breaking it into subsections, buckle the polar jet stream, and send it southward.
-- The problem is that there is no set time period for this to occur. There are cases where the SSW at the pole triggers the blocks almost immediately and leads to cold arriving much faster than our weather models predict, or there is a "lag time" between several days or even a couple of weeks while the warmth from the stratosphere translates down into the middle atmosphere to trigger those upper-level high pressures. Occasionally, the connection even fails and the blocks are never triggered. Now, this is a particularly strong SSW so the thinking is it will, but it is the timing that is the struggle.
-- A polar vortex brings one thing: cold. It does not promise you snow. Last year's December/January visit from our friend the polar vortex did so without any significant snow event here in DC, although nearby Ocean City, Maryland did pick up nearly a foot of snow. The fact we are in an El Nino may increase the odds of seeing some snow, but again, it is not a promise.
The warm pattern should not surprise the readers of our winter outlook. El Nino years in the past, similar to this one, have struggled to keep in the early season cold all the way through the entirety of the winter and tend to feature at least one extended warm "break" from the cold. Our winter forecast actually called for back-and-forth variability during the month of December and we actually expected the month as a whole to average out on the warmer side of things when all was said and done, and as of Tuesday morning, we were currently averaging 0.8° above normal for the month. We still expected more prolonged cold during the latter half of January and through the month of February. If we were to start seeing polar vortex effects starting to pop up in our region, it would likely be after the turn of the New Year with long range models hinting at the second week of January.