burrel2

Well there's several things working against N GA. For one, the 800mb temperature gradient is laid out East to West, which cuts off Georgia's chances at snow before lunch other than the top row of counties. Also the precip moves through Georgia earlier... before the 800mb temperature gradient begins to sag south much. Secondly, the CAD didn't have time to drive much cold/dry air at the 900-950mb level in to Georgia before the storm hits. These layers improve as you go east in to SC/NC,(and later arrival of precip helps). This isn't to say that Northeastern Georgia is out of the running for accumulations, Especially if you have some elevation in the NE Ga mountains. They are actually in a pretty good spot, imo.

If the RAP and HRRR are to be believed. Precip does not arrive in the Upstate until around noon tomorrow. With most of the qpf falling from 1pm-3pm.

The 21z RAP was not kind to the NC foothills. This is through 7am Friday.

21z RAP just came out and it's all snow for the northern upstate,(assuming low levels aren't as warm as depicted.) In fact, it's not even isothermal at my house. I've got a -1C buffer through the column.

There is a CAD element involved for the upstate and NC. Without the CAD our boundary layer conditions would be horrible. With the cad we have a nice punch of sub-freezing air at 925mb, allowing snow to reach the ground as long as the mid-level warm nose doesn't mess things up.

Hrrr is still looking good in regards to the 800mb warm nose for tomorrow. This the latest run for 8am tomorrow. That line on the radar running through the upstate denotes the warmnose cutoff, I've confirmed with soundings. The 18z HRRR kept that line in place for a few hours before shifting it south a little as the heavier precip arrives.

Pickens county close to Clemson.

FYI, the RAP is similar to the HRRR in that it has no warm nose above i-85 at 10am tomorrow morning.

Here is 1pm tomorrow. That bright band denotes partially melted snowflakes at the radar beam level, hence it's a good indicator of where the rain/snow line will be. (assuming the boundary layer isn't too warm).

Me likey the 18z HRRR... keeps the warm nose at i-85 in SC for the duration of the storm. Assuming it's surface temps are off, it's all snow for the northern upstate... 2-4 inches assumig its cold enough to stick. Precip looks anemic for the piedmont of NC though.

The Northern upstate is "in the game" so to speak. No way to know what's going to happen yet. Could get blanked or could get a widespread 2-4 inches. My gut says mostly nothing since every storm I've ever tracked with an 800mb'ish warm nose has verified much warmer at that level than what short range guidance showed. But I think this storm may be different since we aren't seeing a strong push of warmer air with the precip, it's more just where the 0c line settles out/stall tonight with the frontal passage, and then when does it start back progressing South tomorrow? Just an FYI, there will most likely be a slight "push north" of the warm nose for Southeastern NC. I'm speaking for the western upstate here. Any way you slice it, the CC radars should get heavy use tomorrow from our board.

Things have definitely trended better for the southern mountains. They look to get pummeled.

I'm not super concerned about the HRR surface temps since it has a known warm bias in that regard. Also the 3km NAM quickly gets the upstate to 33 when the heavy precip moves in, even with the warm nose up above. FYI, the HRRR may have a cold bias at 800mb for all I know... we will find out.

Here's the end of the HRRR run at 4am tomorrow morning, at the end of it's run. Notice the 800mb temp has not went up, and the cold/dry air has really funneled in to the lower levels thanks to the NE fetch.

I'm very encouraged by the HRRR. The 12z run had far south evolution of the 800mb warm nose. The best I can tell the upstate isn't getting a *push* north of warmer air at 800mb during the storm. It's more like our current 800mb temps are above freezing and the cold air doesn't begin to press until the storm has started. As such, it's imperative that the 800mb between now and tomorrow morning verify on the cold side of guidance,(like the HRRR is showing). If you look at the latest run of the HRRr, 15z. It has that 800mb temp at only around freezing for upstate, SC at 1am tonight. Compare this with the 3km NAM sounding which has it at +3C for the same time. If the HRRR is correct here, I don't expect a push of warmer air at 800mb as the storm comes in, and we may well be around isothermal as the heavy precip moves in tomorrow around 10am. This is my very weenie take on the situation, and what I am clinging to for the moment. HRRR on top, NAM on bottom

The 12z 3km NAM has a warm nose of 4C at 800mb at 4am tomorrow morning for my location. The 14z Hrrr, has the that same warm nose peaking at 1.5C at 3am tomorrow. Edit: it's actually more like .5C Really have to hope the HRRR is on to something with these 800mb temps.

It's running on NCEP. Looks a little drier in the coastal plain of NC as the .75 inch line has shifted from Raleigh to just inland from the coast. Can't tell much on temperatures yet. Hopefully thermal profiles are a little better as a result.

Sleet will still accumulate at 33-34. I was on the wrong side of a warm nose for a storm a few years ago... the lowest my temp dropped to was 33.1, and started rising from that point and I wound up with an inch and half of sleet that also coated the roads.

Gonna come down to nowcasting for the northern upstate of SC. The HRRR and ARW both have my location's sounding going isothermal around 10am just as the heavy axis of precip moves in. The HRRR keeps surface temps at 34-36 though which would be an issue, but I'm guessing it has it's typical bias at play here. On the other hand, the 3km NAM has the warm nose holding strong until 1-3pm for the northern upstate. It shows surface temps at 32-33 however. If, if.... somehow the HRRR and ARW thermal profile is right then the northern upstate could get a 4 to 6 inch past job tomorrow as the heaviest rates come through between 10:00am and 3:00pm. If the 3km NAM is right, then we're going to see a lot of rain/white rain/sleet mix with a possible burst of moderate snow as the back edge swings through with little to no accumulations. It's all comes down to that 800mb warm nose, (and possibly surface temps even if the warm nose is overcome). I would be really nervous in the Raleigh area as it looks like the warm nose will most likely push in to that area during height of the storm. Also I wouldn't bank on the precip outlasting the nose on the backside there. Whoever stays just to north of the warm nose push in that region is going to get 6-10 inches. Whoever is just to the south of it is going to be extremely disappointed. My best guess is Southern Wake gets 1-3 inches of snow/sleet from the storm will the northern end of the county gets the jackpot.

Sorry, I should have been more clear. This isn't a precip type radar. You can just clearly see the transition line due bright banding on the simulated radar.

Green is .5 to 1 inch per hour. Theie maps aren't the most user friendly. https://rapidrefresh.noaa.gov/hrrr/HRRR/Welcome.cgi?dsKey=hrrr_jet&domain=full&run_time=18+Feb+2020+-+18Z

the hrr reflectivity picks up on the rain/snow line via the bright band you can see... where the melted flakes are hitting the radar beam. See the snowfall accum map I posted and it matches that bright band.

look at where that rain/snow line is on the 18z HRRR that just came out.... please be right! That's all the way down to lookout's house.

I believe it only runs at 00z/12z.