I think I told you last night that if we get three inches of snow tonight here on the northern Cumberland Plateau, I’ll eat my hiking boots.
Well, now the National Weather Service has jumped on-board with that possibility. The NWS in Morristown has issued a winter weather advisory for the northern plateau, starting at midnight tonight and continuing through early Saturday afternoon.
Here’s a forecast graphic the National Weather Service published on its website this morning:
You all know me — I will be the first to tell you that I’m not a weather expert, don’t pretend to be and don’t want to be. Interesting weather is a hobby of mine and I try to be well-read on the subject but when it comes time to get serious about the weather, stick to the forecasts from the National Weather Service or your favorite TV weatherman.
But I have to say this: if Scott County receives 2-3 inches of snow tonight, I will be shocked.
There will be fairly decent moisture associated with this system. Forecast soundings from the 0z run of the GFS show about 0.35 inches of precipitable water in the atmosphere through tomorrow morning. So this isn’t necessarily going to be like many winter systems that bring a light snow threat to this region, where moisture is becoming scarce as cold air grips the region. There will be a window of at least 7-8 hours where snow showers will have plenty of moisture to work with, and the snow could fall at a pretty good clip at times. The same forecast soundings show atmospheric freezing levels below 2,500 ft. by 7 p.m. this evening, with surface temperatures in the mid 30s. Theoretically, the rain-snow changeover could be close by that point, several hours earlier than the midnight time frame highlighted in many official forecasts. (Again: that’s data from just one model. Soundings from the NAM model have more of the lower level of the atmosphere above freezing at 7 p.m., with surface temperatures in the low 40s.)
But here’s why snowfall amounts will be skimpy along the northern plateau: ground temperatures. Remember, we’re still early in the season. We were well into the 70s on Monday and we were in the low 60s as recently as yesterday. Ground temperatures are warm. The temperature should fall below freezing late tonight, but not far; temperatures are expected to bottom out around 30 degrees or so. It would take some very high rates of snowfall to cause road conditions to deteriorate. It wouldn’t take as much snow to start creating some measurable accumulation on grassy and elevated surfaces, but snow will have a tough time accumulating under the lighter bands or showers of snow.
I think the forecast of the NWS in Nashville, which calls for a dusting of snow in Jamestown, is probably more reasonable. We could see up to an inch or so on the grass or on someone’s roof, but this is very unlikely to be anything major for areas outside the mountains, from where I’m standing.
Aside from the snow, the NWS has also lowered temperatures in its forecast to 37 for the high tomorrow and 29 for the low Sunday morning. That’s not surprising, given the numbers the models have been spitting out fairly consistently, and the forecast may go even lower as we head into tomorrow. The GFS model just continues to get colder on every run. The 0z run this morning showed a high of 36 on Saturday and a low of 23 Sunday morning. The 6z run a few hours later showed a high of 35 on Saturday and a low of 22 on Sunday morning. Remember, those are raw numbers from one (well, in this case, two) run of one model, and they’re likely a bit too cold. But even if you tack on a couple or three degrees, it looks like a hard freeze is in store for Sunday morning.
Given that, and the gusty winds (to 25 mph) that are expected for Saturday, the last of the fall foliage should disappear rapidly here on the northern plateau.