A full-on pattern change is headed to the eastern U.S. next week, but before that happens, two more shots of snow are possible for the northern Cumberland Plateau region.
FRIDAY: A weak clipper system will dive through the region late tonight and into tomorrow, bringing with it the possibility of some light snow. The National Weather Service’s Morristown office, which covers Scott County and the eastern half of the northern plateau, is all in, forecasting a total of 2-3 inches of snow for this area. But the NWS’s Nashville office, which covers Fentress County and the western half of the northern plateau, isn’t, forecasting little to no accumulation.
There are a couple of issues: One, this system is going to be moisture-starved. Two, temps will warm rapidly on Friday.
Temperatures tonight will drop into the 20s after finally reaching the freezing point this afternoon. The question is how low they go. The NWS is forecasting a low of 20, undercutting both the GFS and NAM models by several degrees. Tomorrow, though, it seems likely we warm above freezing. Even the NWS is forecasting a high of 39, which still undercuts the major models by a few degrees. So if precipitation lingers long enough into the day, a changeover from snow to rain is likely to occur.
As for precipitation, there won’t be much of it. The GFS and the NAM both show less than a tenth of an inch of liquid precipitation. Of course, ground temperatures will be very cold and any snow shower that sets up over the region could quickly create some slick road conditions, particularly in the pre-dawn hours.
If the NWS’s thinking holds, we’ll probably see a winter weather advisory hoisted for the northern plateau later this afternoon. If it doesn’t, we’ll likely see them downgrade the snow accumulation expectations with this afternoon’s forecast. If I were a betting man, I’d bet on the latter.
MONDAY: By Monday, the pattern change is going to be underway. But at the same time, a potent storm system is going to develop and slide across the southeastern U.S., bringing chances of snow to much of Tennessee, particularly the northern plateau and the mountains.
For now, the NWS is being rather vague in their forecasts, and for good reason: there’s a lot of uncertainty with regards to this system. Temperatures are going to be marginal, and the exact tract of the low pressure system is going to largely determine who sees snow and who sees a cold rain as this storm impacts the region.
Temperatures Sunday morning are going to be quite cold — at least in the lower teens, and perhaps even colder than that here on the northern plateau. But the flow will flip to the south during the day Sunday. That will do a couple of things: It’ll start to usher in the moisture that will lead to precipitation — possibly snow — on Monday, but it’ll also warm temperatures above freezing.
Then the system moves in. The European global model, the ECMWF, is faster with the onset of precipitation, while the American-flavored global, the GFS, is slower. Both show a solution that would result in at least some snow for much of Tennessee, particularly the northern plateau.
It does appear that there will be enough moisture available with this system to result warning-level snowfall, if temperatures cooperate. The 6z run of the GFS shows 0.85” liquid-form precipitation, while the 0z run showed 0.80” liquid-form precip. Other major models show at least that much precip.
Most major models show a rain-to-snow scenario, with the ECMWF and the Canadian global, the GGEM, dropping fairly significant totals on the front end for the northern plateau, while the GFS would drop accumulation on the back-end after temperatures fall back below freezing Monday night.
How much snow is impossible to say. Suffice to say that the current look from most of the major models would be enough for a winter storm warning to be issued for much of the region as Monday nears. But if the storm shifts further north, snow potential will drop. Ninety-six hours is a ton of time for things to change in that regard.
Also keep this in mind: warm air advection is going to be occurring on Monday, with warmer air moving into the region. Never, ever under-estimate warm air advection. It’s possible that the arctic air that will be entrenched this weekend is more stubborn than the models are currently projecting, which would enhance snow potential, but if I’m a betting man, I’m always going to bet on the warm air advection being a little more pronounced than what the models show.
Let’s also say this: Be very, very cautious about buying into the ridiculous graphics you see on social media, such as Facebook. For example, this is the one that was receiving heavy play on Facebook yesterday:
That graphic depicts more than a foot of snow for the northern plateau. But what the person posting it didn’t point out is that this graphic is not a forecast. It’s a single run of a single model. Specifically, it was from the Canadian model. There were many other models at the same time — including several with higher verification scores — that did not show snow accumulation anywhere near this, and even other runs of the same model did not show the same.
Case in point, here’s the same model today, and those snow totals are cut in half (almost by two-thirds, in fact):
With all that said, here’s what NWS-Morristown had to say about this system this morning: “Most models generally show the onset of precipitation being all snow, followed by a warm-up during the day on Monday, changing snow to a mix of snow/rain, followed by a change back to all snow late in the event Monday night…Given the differences outlined above, have not gotten too specific with precipitation type or amounts given that this is a low confidence forecast. However, confidence is reasonably high that most/all of the region will experience snow and potentially other forms of wintry precipitation sometime during the Monday and Monday night timeframe. Additionally, higher confidence exists regarding the possibility of a significant snowfall along the East Tennessee and North Carolina mountains, and perhaps portions of far northeast Tennessee and southwest Virginia. However, a much lower confidence exists regarding specific details for snowfall amounts and precipitation timing for much of the valley, including the Knoxville and Chattanooga metro areas, and the Cumberland Plateau.”
Here’s what NWS-Nashville said this morning: “The forecast becomes very uncertain and complex late Sunday through Monday and Monday night. A couple of shortwave troughs will move into the region, helping to develop a surface low pressure system, that will eventually become a major winter storm for the East Coast. Models are continuing to have difficulties handling the evolution of the system at this time. Overall, we expect wintry precip, including some measurable snowfall, across the mid state within the late Sunday through Monday night team frame. At this time, there are too many uncertainties to forecast specific snow amounts, which could vary considerably across the area depending on the exact positions and tracks of the features.”
A TASTE OF SPRING: The pattern change I mentioned will continue to evolve as next week progresses. Any snow that falls Monday won’t stick around too long, with warming temperatures that should be at least 10 degrees above freezing Tuesday and perhaps into the 50s as soon as Wednesday. The current GFS model takes temperatures all the way to 60 degrees by next Thursday.
Here’s what NWS-Nashville had to note in that regard this morning: “After the wintry mess moves away, big changes. Temperatures will recover to near normal levels midweek, then above normal late week as a ridge from the western states expands eastward. Late week will feel like spring with highs climbing into the 60s.”
The big question is whether this warmup will be a prelude to spring or if it’s simply a brief interlude to winter. I wouldn’t necessarily count on an early spring, but winter certainly appears to be on its last legs. The mild weather appears to persist all the way through next weekend and for a week thereafter. That would put us into the last couple of days of February with no more threats of winter weather, should it pan out that way. There are some early signals that Ol’ Man Winter could flex his muscles one last time in early March, but it’s too soon to say for sure.
BOTTOM LINE: A weak clipper system tonight could result in some light snow showers that could temporarily hamper road conditions, but I wouldn’t put off any homework that is due tomorrow if I were a student. The bigger chance for snow is Monday, but by then temperatures are becoming an issue. Winter storm warning-level snows are possible, but only a fool would put money on that at this point…and the main thing is to ignore those graphics on social media that show 12 or 18 inches of snow for our region on Monday. Could it happen? Sure. But it’s not likely — not at the moment, anyway. And after that, the arctic air scoots out of the way for the foreseeable future.