Light snow is possible on Christmas Eve, with snow showers or snow flurries a continuing possibility into Christmas Day, and some minor accumulations and isolated slick spots on area roadways are possible. However, the chances of at least an inch of snow to officially qualify as Scott County’s first white Christmas appear to be diminishing.
The National Weather Service has issued a Winter Weather Advisory for Scott County and all neighboring counties, beginning at 4 p.m. on Christmas Eve and continuing through 4 a.m. Christmas morning. The issue is an arctic cold front that will bring wind and rain, and then rapidly falling temperatures, to the region for the holiday period. Rain will eventually change to snow on Thursday, but it doesn’t appear that much moisture will remain when that changeover occurs.
As recently as 12 hours ago, the National Weather Service was forecasting 1-2 inches of snow for the northern Cumberland Plateau. However, those snow totals have since been halved, and the NWS is forecasting only 0.5-1 inch of snow for the region.
That updated forecast lines up with modeling data that has been coming in throughout the day, showing the moisture out-running the cold air.
The most reliable short-term modeling data suggests that a rain-to-snow transition will occur around lunch time on Christmas Eve. That lines up with the NWS’s forecast, which calls for the changeover to snow to occur at about 11 a.m. on Thursday.
The problem, for snow-lovers, is that the deepest moisture will have exited the region by the time the atmosphere grows cold enough to support snow formation. Earlier forecasts had indicated at least a couple of hours of light-to-moderate snow after the changeover and before the main band of precipitation exited the region.
A developing surface low to the east will eventually slow down the system and allow the arctic air to catch up with the escaping precipitation. That will have some impact locally, as short-term modeling data suggests that light precipitation will back-build, resulting in some light snow showers for the northern plateau region for at least a couple of hours. The changeover will occur with deeper moisture still in place just to the east of the plateau, which is why appreciable snow accumulation is expected in upper East Tennessee. A Winter Storm Watch is in effect for that region.
The timing of the frontal system’s slow-down is the fly in the ointment. If the system were to slow a bit sooner than anticipated, allowing the cold air to catch up, Scott County and the rest of the northern plateau would receive more snow than currently anticipated. However, models currently suggest that isn’t going to happen. If the system doesn’t slow down, it’s likely that Scott County will receive less than half of an inch of snow — generally a dusting or so.
However, occasional snow flurries or snow showers are possible throughout the remainder of Christmas Eve and into Christmas Day, as cold air advection from the northwest wrings out any remaining moisture in the atmosphere in the form of convective snow showers. If banding occurs with these snow showers — which is certainly possible — additional accumulation could become more likely. That’s true throughout much of Tennessee, but especially on the Cumberland Plateau, where upslope flow — the air from the northwest hitting the terrain change west of Jamestown — will help enhance snow shower activity. It’s not uncommon for this region to manage an inch or two of snow accumulation from upslope flow events, though models aren’t currently depicting this possibility very well.
If roads remain wet after sunset on Christmas Eve, or if snow continues to fall, slick spots are likely to develop on roadways as temperatures crash into the teens before sunrise on Christmas morning. The high on Christmas Day is expected to be only in the low 20s. Widespread travel issues are not expected.