Friday’s “snow day” was well forecasted. Monday’s was not.
For the fourth time this winter season — and for the second time in 72 hours — Scott County had at least an inch of snow on the ground on Monday, catching motorists off guard and forcing schools to close as Ol’ Man Winter paid yet another visit to the northern Cumberland Plateau.
He’s been a frequent guest this winter, and we’re a little less than halfway through. For distinct and separate snowfalls have become a somewhat rare occurrence in this part of the world during the relative snow drought that began in the late 1990s and continues today. Granted, most of the snows thus far this winter have been on the light side, not much — if any — over that one-inch mark, with the exception of the first one back on Dec. 1. Some call them nuisance snows: just enough to be a burr under the saddle without really amounting to a whole lot. Nevertheless, they still count.
And there could be more of them.
First, let’s examine the surprise Monday morning snowfall.
This was perhaps the most disruptive snow of the season, for two reasons: For the first time, snow was falling with temperatures well below freezing and ground temperatures already cold. So, the snow readily stuck to roadways as soon as it began. Secondly, no one was prepared for it. Kids were already at school and lots of folks were on their way to work when the snow began to cause road conditions to deteriorate.
So what happened? A major storm system was dumping copious amounts of snow in places like Texas and Louisiana on Sunday. It was always known that there was a chance for some light snow to reach as far north as the Cumberland Plateau, but nothing much was expected from it for two reasons: one, models were showing a well-entrenched layer of dry air in place, and, two, the main storm was far enough away that there wasn’t much forcing to serve as a catalyst for precipitation this far north. As a result, the National Weather Service was forecasting only a 20% chance of snow with a dusting to half an inch of accumulation.
Even in its morning forecast update, which was published a little before 4 a.m., the NWS in Morristown didn’t seem too alarmed at the potential for snow to cause disruptions across the Cumberland Plateau. Temperatures were above freezing in valley locations, warm air advection was working its way north, and the dry air was still in place.
But even several hours earlier, some models had begun to catch on to the idea of more precipitation than originally anticipated, as a healthier plume of moisture streamed from the southwest to the northeast across Middle Tennessee and onto the plateau. As it turned out, not even the dry air could eat up all of that moisture. And the snow falling into that dry air created some evaporational cooling, which drove temperatures further below freezing on the plateau and helped create slick road conditions.
Something else didn’t happen, either: Temperatures during the day didn’t get into the mid 30s, and temperatures aloft didn’t warm enough to change the remnant moisture from snow to rain. So light snow flurries continued off and on throughout the day, and while most roads improved significantly under the midday sun (even though it remained blanketed by clouds), shaded roadways remained very snow-slick as the sun set and temperatures plunged below freezing again.
So, as a result, schools remain closed on Tuesday.
With this fourth snowfall of the season out of the way, what’s next? In previous blog entries, I’ve noted that the ingredients are all here for a winter weather pattern. I wrote last week that Friday’s system and today’s system might not be too conducive for snow here on the Cumberland Plateau, but they would serve to whet snow-lovers’ appetites before the pattern turns truly wintry by the end of this week.
Nearly all of the major teleconnections that meteorologists pay close attention to during this time of year are favorable for intrusions of cold, arctic air with an active southern branch of the jet stream. That’s a setup that screams winter weather potential. Right on schedule, it looks like we’re about to get pretty cold for the end of this week and much of next week. With that said, there are no real storm signals showing up that create alarm at this point. We might see some light snow from the northwest flow if some impulses of energy manage to swing through, but there’s no bonafide winter storm on the horizon.
Could it be that we make it through this period without a serious snow threat? It’s certainly possible. But I wouldn’t bet on it just yet. I’ve used the analogy of baking a cake a couple of times: just because you have eggs, flour and sugar in the pantry doesn’t mean that you’re automatically going to have a cake. But this much we know: the ingredients are all on the table, and right now we’re just waiting to see if mother nature is going to decide to bake cake.
For the next 15 days, the GFS computer model doesn’t have us getting any warmer than 48 degrees on the northern plateau. Keep in mind that we haven’t been out of the 40s since the very warm New Year’s weekend (when we hit 65 on Jan. 2). Beginning Jan. 4, our high temperature has been in the 40s or colder every day. If the GFS model proves true, we could see a stretch of three consecutive weeks with the temperature never getting to 50 degrees. Obviously that’s not the same as having a few inches of snow on the ground or sub-zero temperatures on the thermometer, but it’s pretty impressive for this part of the world.
So, the bottom line is that there’s an ample supply of cold air in place. Right now it just needs a storm system to interact with it. Ironically enough, the same GFS model is pretty much bone dry for the next couple of weeks. So maybe we do get through this without a winter storm threat. But let’s also acknowledge this: this pattern is perfect for a major winter storm. And I don’t mean a nuisance snow of an inch or two, like we’ve seen so far this winter. I mean a major snowstorm, that creates memories. For now, that storm isn’t showing up on the horizon. But we probably shouldn’t let our guard down just yet.