A look at the meteogram (in descending order: temp/wind chill, rain, snow, freezing rain, sleet) . . .
. . . has only rain in the forecast for us tonight.
But, it’s going to be close. Our NWS published this graphic, showing snow close by:
So maybe you’re asking “What’s going on here? It’s sunny right now!”
Around noon, a “clipper” system will be speeding our way. Here’s the HRRR LaterRadar (a name I just made up) at Noon.
HRRR LaterRadar thinks the rain will arrive around 5 PM:
As you can see, there will still be more precip to come tonight as the clipper system works its way through overnight. The question is: will it be cold enough for snow?
Right now, the answer is no…to accumulating snow. We aren’t expected to get below freezing at night. The overnight low is 33°.
But that doesn’t mean we won’t see a few flakes in the air. Why?
The surface temp rarely equals the temp at 2,000 feet, or 5.000 feet, etc. It is usually colder above us (“aloft”) than it is at the surface. Obviously, as the precip falls, it’s doing so through colder air overhead, such that if it’s below freezing up there, the precip can change to snow, and a few flakes may survive and fall to the surface (then melt on contact where temps are above freezing).
Another thing that helps those falling flakes is the process of …NERD ALERT… evaporative cooling. When rain falls through a column of air, some of it will evaporate, which is a cooling process.
We visualize the temps by looking at a “sounding,” which is a snapshot of the atmosphere starting at the ground, and going up. Forecast soundings tell us (among other things) what the models think the temp will be at the surface and aloft.
Here is the forecast sounding for just after midnight. The temp is the red line. The big diagonal white line is the freezing line, so the left of the line is below freezing, the right of the line is above freezing.
This says it’ll be 39° at the surface. At 2,000 feet, the temp will be at freezing, then above 2,000 feet, it’s below freezing. So, it’s possible that any precip that falls will changeover to a wintry mix, fall, and melt at or just before it hits the ground. As you can see from the NAM4 model at 1 AM Thursday (immediately below), there will be some very light precip hanging around overnight:
Areas to our north and east will be colder and/or higher (in elevation), and are more likely to snag some snow tonight/overnight. For everyone except extreme N Davidson Co, nothing is expected, but we’ll be watching these temp profiles in case of shenanigans.
Thanksgiving looks drier, but much colder. Wake up to 33°, with a high of only 42°:
Temps will warm up Friday, Saturday, and Sunday:
This website supplements @NashSevereWx on Twitter.
Categories: Forecast Blogs