Potential remains for some light snow accumulations Thursday night into early Friday morning, as a weather disturbance impacts the northern Cumberland Plateau region.
Exactly how much snow remains very much in question, and there is a lot of potential for no accumulation to speak of. It’s a highly variable system that will do its best to leave meteorologists uncertain about what to expect until the very last minute.
The situation is a closed upper level low that will lift from the lower Mississippi Valley into the Tennessee Valley overnight at Friday. Upper level lows are so notorious for being difficult to predict that there’s a saying associated with them: “Upper level low = Weatherman’s woe.” That’s likely going to be the case Thursday night, as someone, somewhere is likely to wind up in the right position to receive some accumulating snow. Predicting exactly who that’s going to be is almost impossible at this point because the slightest variation in the track of the low will change who that is.
Complicating matters further are the borderline thermal profiles, which leave a razor-thin margin for error. If temperatures at the surface are slightly above freezing, obviously that creates a situation where heavier precipitation rates would be needed for appreciable accumulation to occur.
As of Wednesday morning, the various leading weather models are all over the board with regards to where the upper low will track, what temperatures will be, and how much accumulation will occur.
The GFS global model is showing little to no accumulation for anyone in East Tennessee, the Cumberland Plateau included.
The ECMWF global model, on the other hand, is showing several inches of accumulation for the plateau region.
The NAM numerical model is depicting an inch or two accumulation for the plateau, which seems reasonable.
The HRRR short-range model is showing the potential for several inches of snow, but with a tight gradient that means one area might see appreciable snowfall while another area nearby does not. Taken literally, the current run of the HRRR would be a repeat of the Christmas Eve system, with the plateau on the western edge of accumulating snow and better chances of accumulation in the valley locations such as Knoxville.
For now, the National Weather Service in Morristown is forecasting a 50% chance of snow showers Thursday night, with a low of 31 degrees.
The borderline temperatures should help any significant travel problems from occurring, unless precipitation rates wind up being high, in which case road conditions could deteriorate overnight Thursday into Friday morning. It’s too early to try to pinpoint that possibility. Either way, conditions should improve relatively quickly on Friday, as temperatures are expected to warm into the upper 30s to near 40 degrees as this system departs. In fact, the NWS is forecasting any remaining precipitation to change back to rain around lunch time on Friday.
The next chance for snow will come late Monday into Tuesday. For now, it looks like the system will be far enough to the south that it won’t seriously impact the northern plateau region, but if it winds up further north than currently expected, Tennessee will be in play for some wintry weather.