At least 422* times per winter (*approximately), the question of whether “the polar vortex is coming” seems to come up. The sources are many: Rogue social mediarologists who want engagement, well-intentioned meteorologists who are just trying to explain something but the wrong takeaway gets amplified, not-well-intentioned meteorologists who can’t help themselves, and weather enthusiasts who are misinterpreting model guidance.
We are in one of those phases now, so is the polar vortex coming for us again like it (sort of) did in January?
Just to get the science lesson quickly out of the way: Recall that the polar vortex is always there. It’s a permanent feature that typically sits over the North Pole, keeping the hemisphere’s coldest air in the polar region. When we refer to the “polar vortex,” what we’re really referring to is the stratospheric polar vortex, which sits miles above the North Pole but keeps the cold locked in. During the wintertime, every so often something will happen where that cold can be dislodged and dumped into the mid-latitudes leading to cold air outbreaks over the North America, Europe, or Asia. How does that happen? Periodically, you’ll get a warming event in the stratosphere that eventually works downward, first displacing or splitting the polar vortex and then leading to high latitude atmospheric blocking that warms the Arctic and sends cold south. This is what can unleash some of that more noteworthy cold air.
The process is really complicated and fairly often, stratospheric warming does not lead to significant polar vortex disruption. But almost every time there is a warming event, you now hear about it because of what I noted in the opening paragraph.
So what is happening now?
If you look at the forecast weather map today, you can see a pretty anti-winter look in the Eastern half of the country, with very mild air from Hudson Bay south to the Gulf. The West is stormy. Most of the cold is up near Alaska or Siberia and over Scandinavia.
Over the next 10 days or so, this pattern is going to change rather dramatically. The ridging in place from Hudson Bay to the Gulf will weaken. The pretty neutral pattern from Alaska through the Arctic to Greenland is going to block up and warm. This will allow cold to displace back southward into lower latitudes in North America. The real serious cold is probably going to go on the other side of the globe, dumping into Russia and portions of Central Asia. One way to proxy this is to look at the Arctic Oscillation (AO). In a nutshell, the AO is a barometer for high latitude blocking over the Arctic. It’s far more complicated than just using one index to determine the fate of the weather. But in situations like this, it can help.
What does it tell us? When the AO is positive, it generally indicates that the Arctic will be cold. It can be assumed most of the time that the polar vortex is sort of in place, in its home over the North Pole. When the AO turns negative, it tends to mean that something has happened in the Arctic that leads to milder conditions and a weaker polar vortex, allowing cold to meander away from the North Pole and toward the populous mid-latitudes. Notice on the chart above that back in mid-January, we had a negative AO, which led to the cold outbreak. Also notice that not every negative AO produces excessive cold! We had a pretty strong bout of negative Arctic Oscillation conditions back in early December, which coincided with Houston’s most recent 80 degree day. We did turn colder after that day, but not excessively so.
Anyway, the AO is forecast to go negative, strongly so around mid-February. This gets a lot of meteorologists’ attention, and justifiably so. It’s a strong signal for strong blocking in the polar region. And indeed, if you look at the Climate Prediction Center’s outlook for days 8 through 14, it shows colder than normal temps forecast over a broad portion of the Lower 48.
Now, this map is plenty cold for sure. But it’s also moderate confidence. In other words, we’re not super confident in major cold right now. This meteorologist would say we are moderately confident in moderate cold. Frankly, modeling has been a little underwhelming with respect to the cold in mid-February. Some of the modeling that picked up on the ferocity of the January cold early on is not exactly doing so now, though it is forecasting cold. So at this point at least, a repeat of a January 2024-like cold outbreak in Texas seems like a longshot. But it’s going to be cold, and no, we cannot rule out a another (modest) freeze before winter ends.
This setup may be more interesting for the Southeast, particularly with a lot of moisture getting pumped in from California again. If you could perhaps combine some of that moisture into a well-timed low pressure system in the Southeast with some meaningful cold air, we could see some wintry weather in the South or Mid-Atlantic somewhere through late month.