On a previous post, we talked about how the teleconnections weren’t supporting much in the way of cold and snow potential for the Mid-South region through the first half of January, but that signs were pointing towards a potentially more winter-like pattern for the second half of January.
While there’s no true source of arctic air to funnel extreme cold into our region through the first half of the month, it now looks like the return to winter weather potential could be a little ahead of schedule.
Let’s break it down.
The pattern that we’re dealing with is a combination of a negative North Atlantic Oscillation and a negative Arctic Oscillation. Real quickly, let’s recap what these are: The NAO is a measure of storminess in the northern Atlantic Ocean region — think places like Greenland, Denmark, etc. The AO is a measure of storminess in the Arctics. These are just two of several teleconnections that are closely monitored by meteorologists, but they’re perhaps the two most easily understood in laymen’s terms. In general, the combination of a -NAO and a -AO leads to colder and sometimes stormier weather in the eastern United States. A -AO allows the jet stream to shift further south and unleash colder air into the continental U.S., while a -NAO brings lower air pressure to the eastern U.S., often resulting in cold outbreaks and increased storminess. A -NAO is especially effective when a so-called “Greenland block” develops. This refers to high pressure over the northern Atlantic basin, which prevents arctic air from circulating in a counter-clockwise direction around the pole as it ordinarily would. Just like a traffic jam, if the air isn’t flowing smoothly, the cold air will back up. Because it has to go somewhere, the eastern U.S. often winds up being colder as a result. If you throw in a positive Pacific North American ridge index — which is a measure of air pressure in the eastern Pacific Ocean — that can help funnel colder air into the eastern U.S. All of these things can work together for a relatively cold weather pattern that ultimately impacts Tennessee.
So far this winter, we’ve seen a -NAO, -AO and +PNA combination dominate — which is why we’ve been relatively cold with multiple snow chances in Tennessee even though we’re in a La Nina winter (which often translates to a milder winter — which is what long-range meteorologists forecasted).
The combination of a -NAO, -AO and +PNA doesn’t always translate to colder and snowier weather in East Tennessee. But the chances of seeing winter storms develop with that look are far higher than when that combination is flipped. Throw in the possibility of a sudden stratospheric warming event that could result in a displaced polar vortex, and you have all the ingredients for cold and snowy weather for at least a couple of weeks beginning in mid January. Anyone who has spent much time in the kitchen knows that having eggs, flour and sugar doesn’t automatically equal cake, but you can’t have a cake without those ingredients. That’s where we stand right now. The ingredients are in the pantry. Whether they all come together remains to be seen.
But we’re starting to see models hone in on several threats over the next 7-12 days. Right now, it doesn’t look like we’ll have an especially deep supply of cold, arctic air, but there is cold air lurking closely enough nearby to create problems if the storm tracks work out correctly.
The first one to keep an eye on is Thursday night into Friday. For now, it looks like it’ll probably wind up being a little bit too warm for snow here on the Cumberland Plateau. (And there’s not a lot of moisture to work with, anyway.) The GFS computer model is showing a big winter storm for the western Carolinas, while we see only a little light snow here that doesn’t amount to anything. But the ECMWF — which is the European counterpart to the GFS — is showing appreciable snow accumulation for much of East Tennessee. Taken verbatim, it still leaves the plateau region generally snowless, but accumulations can be found much closer to home on the ECMWF than on the GFS. For now, this is a storm that probably won’t amount to much of anything for the Cumberland Plateau, but it’s worth keeping an eye on.
After that, there are storm chances that appear to set up about every 3-4 days. And while none of them are showing up as a winter storm for the plateau region at the current time, any of them could potentially develop into that as we get closer. And it looks like true arctic air could return to our region by around Jan. 17-18.
At the very least, it looks like the next couple of weeks are going to feature seasonably cold temperatures, with no real warmth to speak of, even if we don’t see a single snowflake fall. While things could change, models currently aren’t showing temperatures getting out of the 40s at any point in the next 15 days. That may not be anything to write home about, necessarily, but it’s a far cry from what many climatologists were expecting a few weeks ago, when it seemed like we could see a much warmer-than-average month of January.
For now, the potential weather pattern that lies ahead is still evolving. Maybe it winds up being a dull and boring pattern without much in the way of snow and cold. Or, maybe it winds up being quite cold and snowy. The ingredients are there. For now we wait to see if mother nature decides to bake a cake.
