Ever since Bing Crosby sang about it during World War II and sold more than 50 million copies of the song, Americans everywhere have dreamed of white Christmases.
Historically, white Christmases are pretty uncommon in East Tennessee. There’s only about a 15% chance of a white Christmas with at least one inch of snow on the ground in any given year on the northern Cumberland Plateau. There have been two white Christmases in Oneida in the past 20 years, with the last occurring exactly 10 years ago.
This year is extremely unlikely to rival that white Christmas in 2010, when Christmas morning dawned with more than half a foot of snow on the ground, but it looks like chances are fairly good that this Christmas will be one of the ones that Crosby sang about, with a strong arctic cold front swinging through the region on Christmas Eve to deliver a rain-to-snow scenario and much colder temperatures.
The National Weather Service forecast for Oneida is for a 90% chance of rain changing to snow on Christmas Eve, with precipitation chances tapering to 50% by the afternoon. The day will start rather mild, with temperatures in the 40s, but falling temperatures are expected throughout the day on Thursday. Depending on the exact timing of the cold front’s arrival, temperatures could fall to near freezing by around lunchtime on Christmas Eve, and be below 28 degrees by sunset.
Moderate rainfall will be moving out of the region when the cold air arrives, creating a classic cold-chasing-moisture scenario that is fairly common in East Tennessee during the winter months. As temperatures drop, whatever moisture remains will transition to snow, and light accumulations are possible across the region, particularly here on the northern Cumberland Plateau.
Forecasters at the National Weather Service are closely monitoring the approaching frontal system. In its forecast discussion published Tuesday afternoon, the NWS’s Morristown office notes how tricky the forecast is.
“Arctic fronts are tricky to forecast as guidance usually has a tough time resolving these fronts and the depth of cold air,” the discussion noted, before going on to lay out several scenarios that are possible as the colder air moves in.
Taken at face value, all major computer guidance models show the potential for several inches of snow accumulation across the northern plateau region. However, most of those depictions are likely overdone. Cold-chasing-moisture scenarios don’t typically produce much snow even in favored areas like the plateau, with the moisture escaping as the cold air arrives. For that reason, the NWS’s Nashville office is forecasting little to no accumulation, with perhaps up to one inch on some parts of the plateau.
Indeed, one major medium-range model — the GFS — had been depicting 8 to 10 inches of snow consistently until just a few days ago, when it began to rapidly downgrade its projections. It now projects 1-2 inches of snow for Scott County.
However, as NWS-Morristown notes in its forecast, this is an unusually strong arctic cold front, with steep lapse rates that will favor heavier bands of snow. If — and it’s a big if — the cold air arrives fast enough, there could be a short-lived period of relatively heavy snow that could accumulate relatively quickly. Additionally, some light snow showers or snow flurries will likely out-live the departure of the heavier precipitation, which could mean some minor accumulations.
It’s going to be impossible to predict exactly where — if anywhere — heartier snow accumulations occur. Areas that wind up under heavier bands of snow could receive modest accumulations, while areas a short distance away receive very little snow accumulation.
As a general rule, this setup of cold-chasing-moisture is one where forecasts of several inches of snow often wind up giving way to less than an inch of snow. That could well be the case with this particular system, but chances seem relatively good that anyone on the northern plateau between Oneida and Jamestown and neighboring areas see at least an inch of snow and — thus — a white Christmas. (For the record, the NWS’s official forecast for Scott County is for a half inch to one inch of snow.)
No matter what, it looks like snow will be in the air on Christmas Eve with much colder temperatures by Christmas Day, so it’s going to at least feel like the Christmas that Bing Crosby sang about. Temperatures will be in the mid teens by sunrise on Christmas morning, and high temperatures on Christmas Day will not get out of the low 20s before we plunge back into the mid teens Christmas night.
The warm-up will be quick and pronounced; Saturday’s temperature will likely hit 40 degrees, and temperatures will be back to near 50 by the end of the weekend.
The good news for those with travel concerns is that widespread travel issues shouldn’t occur if snowfall is on the low end, as currently predicted. However, some isolated issues are certainly possible, with temperatures plunging so quickly and deeply as at least light snow showers are still occurring. Any areas that wind up under heavier bands of snow, if they develop, could see more substantial road hazards.
The forecast, including timing of the changeover from rain to snow, should become clearer on Wednesday. However, short-term modeling currently indicates that a changeover from rain to snow could occur early in the day on Thursday, well before lunch.