GaWx

The major indices are all combining to help make this SE winter storm and cold happen: PNA over +1 leading up to and during storm AO had gone to below -3.5 and still ~-2 during storm NAO period of sub -1 leading up to and during storm MJO cold supporting weak to moderate left side leading up to and during storm The last time in met. winter with this strong a combination of +PNA/-AO/-NAO along with left side MJO was way back on 2/7/10! Before that, it was way back in Jan of 1985 (several days: 4,5,7, 17). Before that was 1/15/1977. So, cherish this very rare combo that has occurred only about once every other decade or so. Each of these three periods was associated with very memorable SE wintry events including deep SE following within a few days: -2/7/10: preceded a major SE snowstorm by 5-6 days (2/12-13/10) with 8” at Columbia for example and NW FL snows of 1” on 2/12 and 0.5” on 2/14 -1/17/85: preceded by just 3-4 days either the coldest or 2nd coldest lows on record (back to late 1800s) in much of SE US -1/15/77: preceded extreme cold in SE US by 2-4 days, which included snow in many areas including much of FL with light accumulations central FL and flurries way down to Homestead and the Bahamas! -1/7/24: ?

12Z GFS sleet for AL/GA/SC: wide area and looks rather impressive, Tony, with possibly ~0.5” at your abode, about the most I’ve seen yet for you and many of these areas on any model’s run (note the 0.7 at Athens): @dsaur Aren’t you just north of the Experiment station? But as you always say with sleet, the more worrisome ZR is usually lurking though this is not high in your area…maybe 0.10”:

It does except this model has it changing to rain Fri evening in/near downtown ATL.

I do not recall.

12Z Icon 850s are +1C to +3C and thicknesses near 552 dm in this area of S GA showing as snow. If I thought this was real I wouldn’t be considering driving 250+ miles to what could end up mainly as an icestorm.

12Z Icon “snow” 6Z Icon “snow” but 850s are +1 to +3C:

6Z Icon: this isn’t real. Otherwise I wouldn’t consider driving to the ATL area. 850s are +1C to +3C and 2m temps are near or just above 32F. So it could be from sleet. But QPF is only ~0.25 max in the E portion for that period. The model is treating it like snow! 0.25” in form of sleet couldn’t accumulate that much.

Fellow wx weenies, I need some advice. If you were in Savannah with no chance for wintry precip, would you drive 4-5 hours to N Gwinnett county (NE of ATL) on Thu if family or friends offered you a room to stay in for the weekend and enjoy it with them? It is a few miles S of the Mall of GA. This could easily be ATL’s biggest winter storm in 11 years and years til the next major one. I haven’t seen a flake or pellet in 7 years! But I’m worried ATL is going to get mainly ZR. While ice looks pretty and would be exciting to see, heavy ZR could mean long outages/no TV/cold inside and no snow or sleet to look at and walk in. So, it could get miserable. If I knew it were going to be nearly all snow and sleet, it would be an easy decision. Weenies, what would you do?

18Z GFS much IP/ZR ATL vs 12Z with still heavy (~4.5”) snow (vs 5.5” 12Z). About same qpf. Precip types vs 1000/500 mb thicknesses still suspect (though not quite as off). So, I’m still thinking too heavy snow in southern part of snow accum. ZR: increased from 0.1” to 0.25” ATL; ip also increased from near 0 to 0.10”

Yep. For example, ATL moved from 3.5” of snow on 12Z to 0.5” on 18Z.

18Z Icon snow: heaviest is further north than 12Z

I was there for the 1/21/87 ATL snow. It had no sleet or ZR on the borderline. Instead it was heavy snow in most areas but heavy rain (with possibly some flooding) just to the SE. This one looks different due to potential significant ice in possibly a wide region in the transition. The latest CMC and NAM say mainly ZR ATL.

Looks like mainly ZR downtown ATL on the 18Z NAM with ~1” of snow pretty similar to 12Z CMC. Also, note that all of the snow is well north of the 552 thickness line, which makes sense unlike the 12Z GFS’s snow going to ~555.

Interesting! That’s a bold call for Atlanta. Your map has mainly plain rain (light green) all the way up to Sandy Springs (N of Perimeter) with no snow and just a little ice. This is bold because all 12Z models but UK have further south downtown ATL at 30-32 (UK starts 34 but it has thermal issues and still then drops to 32 with heavy snow) GFS: 5.5”; little IP/ZR; qpf 0.95” UK 5”; little IP/ZR and some rain lol; qpf 0.85” Icon 3.5”; qpf 0.95” Euro 2”; moderate IP/ZR; qpf 0.58” CMC 0.2”; mainly ZR and IP; qpf 0.70”

Today’s Euro weeklies are still full steam ahead fwiw for -PNA/SE ridge in the first half of Feb.

That depends much more on colder 850s than it does on surface dewpoints.

Not me. I’m over 100 miles away from the good stuff! I can relax because there’s nothing to worry about since there’s virtually no chance of anything significant nearby.

12Z models’ snow/other wintry/qpf for downtown Atlanta: huge range: GFS: 5.5”; little IP/ZR; qpf 0.95” UK 5”; little IP/ZR and some rain lol; qpf 0.85” Icon 3.5”; qpf 0.95” Euro 2”; moderate IP/ZR; qpf 0.58” CMC 0.2”; mainly ZR and IP; qpf 0.70” AVG: 3.2”; qpf 0.81” So, anywhere from heavy snow, generous qpf, and little IP and ZR of GFS/UK to CMC’s almost all ZR/IP and more moderate qpf. I wouldn't want to be an Atlanta forecaster right now! Anyone have a good feel for ATL yet?

12Z Euro: ZR: IP: qpf:

I’m questioning more the snow line on the 12Z GFS. Snow in some places with thicknesses as high as 555 mb, a low tracking near Cordele, GA, and 5-6” of snow in Atlanta don’t usually all go together. I’d say that on the GFS either the thicknesses are too high (and will end up being lower like that of UK/Icon), the low track is too far north, and/or the heavy snow line is too far south.

This UKMET map, like CMC, makes much more sense in relation to 1000/500 mb thickness guidelines with it having all the snow with thicknesses lower than 548 dm. But then it has rain in NC up to 540 line, which doesn’t jibe. Aside: Note that UK has 547 line much further south than GFS/CMC. Thus it makes sense that ATL has heavy snow on the UK.

I hate to see this but mainly ZR instead of mainly snow actually makes more sense for much of this area based on 1000/500 mb thicknesses guidelines. Also, I’m considering the track of the low.

Here’s the 12Z CMC for the same time, which much better concurs with the guideline of a 546-7 thickness snow line: this is like night and day vs the GFS! Again for comparison, here’s GFS with snow with thicknesses almost to 558!

Is anyone else bothered by this thickness/precip type 12Z GFS map? Typically in the SE the snow line is near 546-7. But this shows snow with thicknesses well over 552! How can this be? This is so odd! Can anyone explain this? I’d be highly suspicious of precip types on this.

12Z Icon 10:1 clown has 1.4” of snow at Statesboro, GA, from 0.21” of qpf. That can’t be right with 850s of +2C and surface temps of 34+. It could be sleet but 0.21” of liquid equivalent of sleet won’t accumulate to more than half that and that’s with no melting (temps of 32 or lower). And then it has accumulation up to 0.2” in my area and 0.1 into far N FL. CHS is 37+ and 850s are +2 and it shows 0.4”. Impossible! All of the southern end of this map looks way overdone based on its own parameters. Looks like an algo issue: