Afternoon temperatures in the lower 40s will turn dramatically colder as a cold front pushes through this evening. We'll drop from the upper 30s to the upper 20s between sunset and midnight as wind switch to the northwest.
Moisture along this evening's front should result in some scattered sprinkles changing to a brief period of flurries or light snow showers. The general window of opportunity for the Mid-South will be between 6 p.m. and midnight. If you live in Kentucky, expect it to start closer to 6 p.m. and if you in southern Middle Tennessee it may take until midnight to arrive.
With cold air rushing in at all levels of the atmosphere, it won't take much moisture to produce some snowflakes. The morning run of the GFS model estimates a 21 to 1 snow to liquid ratio between 9 p.m. and midnight. That's about twice as much as the usual 10 to 1 snow conversion. Sometimes in the South our ratios are as low as 5 to 1 when temperatures are right on the freezing line and wet snow is involved.
The GFS model tries to develop 0.4" of snowfall for the Nashville area before midnight. That's much more than the prior model runs were calling for and has grabbed my attention. Given the latest data, I would not be shocked if some areas ended up with a quick dusting. The rest of the night's very cold temperatures in the 20s and possibly upper teens by daybreak would allow any light snow that falls to stick around.
Important disclaimer: although the GFS model is calling for 0.4" of snowfall, I'll stick with the phrase of "a dusting" for Nashville and the surrounding metro counties. I anticipate the higher terrain east of I-65 toward the Cumberland Plateau will have an upslope effect on the northwest winds and squeeze out a few more snowflakes, possible around a half inch or so by midnight.
The attached images show the various computer model forecasts for this evening. First is the GFS, which shows 0.25" of snow and 0.5" in the higher terrain east of Nashville toward the Cumberland Plateau. Second is the high-resolution, short-term NCEP RAP (Rapid Refresh) which also shows 0.25" of snow for parts of the mid-state, and a little more, around 0.5" for the Cumberland Plateau. Third is the outlier, the high-resolution NAM, which outputs a 0.25" to 0.5" of snow for the mid-state but up to 1" on the Cumberland Plateau.
I like the second look the best (the NCEP RAP) because I believe by the time the sprinkles change to flurries we'll have limited moisture to work with. With those high snow to liquid ratios I mentioned on account of all the cold air, however, I would not be shocked with a dusting of some snow by midnight.
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