So you've been enjoying the shirt-sleeve late November weather? Well, prepare yourself. Because major changes are on the way. And soon.
November proved to be a warm month. We closed out the month with an official high temperature of 65 degrees yesterday. Meteorological winter begins today with the warmth hanging around, and it looks like we'll see a high near 60 for the 69th annual Scott County Chamber of Commerce Christmas Parade on Saturday.
Enjoy the weekend and its very un-December-like warmth. Because it isn't going to last.
Weak La Nina patterns, like the one we're in, are hard to read. Sometimes they lead to prolonged warmth during the winter months. We saw that in December 1984, and some predicted it would be a warm December because of that. But sometimes they also lead to prolonged cold before or after the warmth. We saw that in January 1985, which saw a trifecta of winter storms slam the Cumberlands and paralyze this region for weeks.
It has become probable that December is going to feature some of that prolonged cold. That isn't to say it's going to be a stormy and snowy December, though there certainly could (and probably should) be some snow threats in the weeks ahead. It's just to say that it's going to be very different from November.
The Madden-Julian Oscillation, which measures atmospheric conditions in the tropics, is moving through Phases 7 and 8, and on into Phases 1 and 2, as we move through the month of December. That means nothing to you if you aren't a weather nerd, but, basically, 7, 8, 1 and 2 are the cold phases of the MJO.
In addition to that, the Arctic Oscillation — a measure of atmospheric conditions in the arctics — is still in shallow negative territory and getting set to dive deeper, which is a good look for cold air to spill into the continental U.S. The North Atlantic Oscillation, which measures storminess in the northern Atlantic Ocean region, could trend into positive territory for a while, but is more likely to stay neutral, and could plunge into negative territory about a week into December. And the Pacific North American ridge index is finally moving into positive territory.
With the AO conducive for arctic air to spill into the Lower 48, and the PNA indicating ridging in the eastern Pacific, that should be conducive for that cold air to be forced into the eastern U.S. in general, and the Southeast in particular. If the NAO goes negative and blocking sets up in the northern Atlantic, that's only going to enhance the idea of a cold month of December.
So that's where we are. Because of these indications, and others, NOAA's Climate Prediction Center is forecasting a colder-than-average month of December for the eastern U.S.:
That doesn't mean there won't be some warmth in there somewhere during the month, just that the month as a whole should be cold. For now, modeling is showing pretty good indications that the first half of December, at least, will be consistently cold. Take a look at the CPC's forecast for Dec. 8-14:
Here's how it's going to set up: After a warm start to next week, a cold front is going to blow through on Tuesday. Once the winds and rains blow out in the wake of that frontal passage, much colder temperatures will arrive. We should be in the mid 60s on Monday and could be close to that on Tuesday, then Wednesday may see us struggle to get out of the 30s. And that will be the kind of temps we see for at least the next couple of weeks.
The latest run of the GFS forecast model is particularly cold. After the frontal passage late Tuesday, it doesn't have temps getting out of the 30s again for a week. That's likely too cold; the raw data from the model usually is. In fact, output statistics from the same run of the model show us getting into the 40s each afternoon. But that's really quibbling over a few degrees either direction. The bottom line is that it's going to be much colder. And by next weekend, we could see temps in the teens at night, which would be the coldest air of the season thus far.
Initially, the pattern looks dry. But there are signals of a storm system sometime around Dec. 13-16, and if temperatures and other factors cooperate, that might be the first winter storm threat of the season. It's way too soon to say at this point.
One thing is for sure: this is the most "winter-looking" December we've had, at least as it is setting up, since 2010, when we had two major winter storms in our region during the month. That was also our last white Christmas here on the northern Cumberland Plateau.
Of course, it's much too soon to say what this weather pattern is going to be doing at Christmas, which is still more than three weeks away. It may very well have relaxed and allowed warmth to return by then. But if one had to bet, based on the signs that are appearing right now, it would probably be safer to bet for a cold Christmas than a warm one.
After the first half of the month, though, I'd probably not be willing to bet on anything. However, the latest run of the GFS model, referenced above, has us plunging all the way to one degree at the very end of its run, on Dec. 17. That would be in the immediate aftermath of the storm that's going to impact the eastern U.S. somewhere around Dec. 13-16.
The bottom line: the 60s we've been enjoying the last few days are about to go away. Winter is about to arrive, and it's going to stick around.
Eye to the Sky is a weather blog by Independent Herald editor Ben Garrett. Garrett is a weather enthusiast who has long blogged about interesting weather on his personal website. He is not a professional forecaster or a meteorologist and information on this blog should not be considered a substitute for forecasts, advisories or other products from the National Weather Service.