A few hours of light freezing rain or drizzle are possible across the northern Cumberland Plateau region early Monday morning.
The National Weather Service at Morristown highlights the threat in a hazardous weather outlook published Saturday afternoon, saying that no impacts to utilities are expected, but some slick spots may develop on roadways. In a graphic prepared for its forecast, the NWS says about five-one hundredths of an inch of freezing rain may be seen in Scott County, with lesser amounts south into Morgan County and east into Campbell County.
At issue is a disturbance that is poised to trek across the region on Monday, just as the arctic air mass that has been in place for the past week is being eroded. Precipitation will likely be very light, and temperatures will warm well above freezing on Monday, so this will not be a high-impact event. But with the ground frozen -- very much so -- from the past week's temperatures, it won't take much to cause some minor travel issues as the day begins. That's sure to be of interest to students and teachers across the county, who will be hoping to use their second built-in snow day on Monday.
So, what are the chances that we actually experience enough freezing rain to force schools to close? There's a lot of uncertainty (isn't there always when it comes to winter weather in the South?) but it could happen.
A southerly flow will kick in ahead of the storm system on Sunday. This will bring us our warmest temperatures in a week on Sunday afternoon, when the NWS is forecasting a high of 37. The question then becomes whether we'll cool below freezing Sunday night, and what time precipitation will arrive early Monday morning.
Interestingly, our forecast has been trending colder. We originally were expected to drop into the low teens tonight, and climb into the 40s on Sunday. Now, however, the forecast is for only the upper 30s on Sunday, after a low in the single digits tonight. The NWS was forecasting a low of 31 Sunday night; it's now forecasting a low of 29.
I blogged a couple of days ago that warm air advection is often under-estimated here on the Cumberland Plateau, where there are no terrain features to help block warm air advection. Even though higher elevations are typically cooler than lower elevations, the opposite is often true when a southerly flow kicks in ahead of an approaching storm system. Once the southerly winds kick in, you often see warmer temperatures in Oneida and Crossville than you do in Knoxville and Oak Ridge, as the warmer air builds in from the top down, and the valley — sheltered by the plateau to the west and the Smoky Mountains to the east — sometimes sees colder air pool up.
There have been many times when meteorologists were forecasting freezing rain for our region and it just didn't happen because the southerly flow prevented temperatures from dropping below freezing during the overnight hours. I wouldn't be surprised if the same happens tomorrow night. But that's obviously not guaranteed.
It's worth noting that while the GFS forecast model has lowered its projections for our temperatures tonight and tomorrow, it continues to hold temperatures above freezing tomorrow night. Model output statistics from the GFS show us dropping only to 35 degrees tomorrow night. Raw data from the model has us dropping briefly to 30, though we're back to 32 by sunrise and above freezing by 10 a.m.
It's also worth noting that the 3K NAM forecast model and the original NAM model are both colder than the GFS, and have us around 28-29 degrees at sunrise on Monday. The Canadian is a little closer to the GFS, but is slightly colder.
Our first real indication of what we'll experience in terms of freezing rain will come tomorrow afternoon. How warm do temperatures get? The warmer they get before the sun starts to set tomorrow, the harder it will be for them to cool below freezing during the overnight hours. If we exceed our forecast high of 37, that might be an indication that freezing rain isn't going to happen. It's worth pointing out here that the HRRR, a typically reliable short-term model that updates hourly, now shows us topping out in the low 40s on Sunday afternoon. And the latest run of the 3K NAM, which is coming in as I type this, is coming in slightly warmer than the previous run of the model for Sunday afternoon.
Of course, temps are just half of the equation. Even if temps are below freezing, there can be no freezing rain without...well, rain. The 3K NAM does show very, very light precipitation over our region around sunrise Monday. As cold as the ground is, any drop of rain that falls with temps at 32 or below will freeze on contact. However, as light as the precipitation is showing up on the models, it won't be too shocking if it doesn't materialize.
By Monday afternoon, our temperature should be at 40 or above, and any ice that accumulates will quickly melt. But it only takes an hour or two of freezing rain to cause problems Monday morning.
Further out: It still looks like we're going to be in the 60s by Wednesday and may push close to 70 on Thursday, which is going to feel like a sauna compared to the temps we've experienced recently. But a stronger storm system is still on the table for the end of next week, and that could have some wintry mischief attached, followed by another round of cold temps by next weekend, before temperatures get even warmer the following week. Next weekend could be our best shot of accumulating snow thus far this winter, but it's still a long way out and subject to many changes. If you're hoping for snow, you better place your chips on next weekend. If we miss out then, it'll likely be the end of January or early February before the pattern reloads and we see another chance of accumulating snow.
Eye to the Sky is a weather blog by Independent Herald editor Ben Garrett. Garrett is a weather enthusiast who has long blogged about interesting weather on his personal website. He is not a professional forecaster or a meteorologist and information on this blog should not be considered a substitute for forecasts, advisories or other products from the National Weather Service.