GaWx

12Z Icon qpf

The Arctic sfc high ahead of the low on the 12Z NAM is 3+ mb weaker than that on the 6Z and much weaker than what’s on the 0Z. Any opinion about this?

12Z NAM: ZR IP Qpf

0Z EPS snow by member:

0Z EPS woke up with a significant increase in snow!

He’s transformed into Rain Cold.

0Z GEFS snow:

0Z Euro ZR: IP: @dsaur Qpf:

The 18Z GFS would easily give the Atlanta area as a whole its most impactful storm since 2/12-13/2014.

But even if so, that coldest may not include much of the S US, at least in the means as we’re going to be quite cold these next 2 weeks it appears.

Today’s Euro Weekly for 1/20-6 once again has cold dominating much of the US (especially N Rockies to MidAtlantic) though this continues to be the final week of the cold week streak (that includes the 2 weeks prior) before the long advertised change to much warmer:

About an hour ago it was 40F warmer here with low 70s and winds gusting to 40 mph. It has now dropped to mid 60s.

Tony, Based on looking at decades worth of old maps of 850s at the time of SE winter storms, I’ve found that the sweet spot for significant sleet is +1 to +2C at 850 mb combined with good wedging. The models that aren’t delaying the precip have in or near that sweet spot for your area for most of the storm fwiw (yes it will change but you’ve got a decent shot). Colder than that is snow and warmer than that is often ZR, especially +3C+.

12Z EPS: The 2m temps (along with H5 heights) dropped noticeably vs the 0Z (this as of 1PM Fri):

12Z EPS mean snow: some increase most areas vs 6Z:

12Z Euro: Due to light precip moving quickly into antecedent very low dewpoint air, it has an interesting period early in this storm with mainly ZR along with a little sleet Fri morning within an area of central GA including Columbus, Macon, Sylvania, and Statesboro. @Shack Dewpoints at 12Z Fri: still as low as mid teens as precip moves in qpf 12Z to 18Z Fri coming right into that very dry air Even at 11AM, temps are still down at 32F with the precip falling along with cold mainly NE flow in EC GA (winds not off the much warmer ocean): Result are these precip types with an emphasis on ZR in central GA: This is mainly a curiosity now but does show things could get interesting unusually south if the precip comes in early enough there on Fri morning. The Icon and GFS are similar. Here’s the GFS radar simulation as of 12Z on Fri:

12Z UKMET has the ATL area as the jackpot with 5-5.6”. This is actually a reasonably accurate map when considering their other variables of <0C 850s, temps of 32-33F, and plentiful qpf of 0.6-0.7”. If that were to verify, it would be slightly more than they got in Jans of 2011 and 2002. The last time ATL officially got 5” was in Jan of 1992 though the northside got much more in March of 1993. So, I wouldn’t bet on this much occurring at this point, especially with other models having much less due to warmer upstairs like at 850 mb. It is a high outlier for snowfall in that area compared to other models though it has shown it on the last 3 runs: 4”, 3”, and now 5+”.

It shows ZR/IP. You can see a tiny area of it south of RDU. But UK clown maps are questionable where there’s IP/ZR.

12Z GEFS mean snow (excludes IP/ZR):

The CMC has about the strongest cold bias of the major models at the surface. But the CMC/RGEM often do best in icey/CAD situations.

12Z CMC ZR: major icestorm with 1”+ ZR ATL, Gainesville, Athens, Augusta, Columbia Sleet: @dsaurgets some

12Z GFS ZR: significant in some areas. This would be a major winter storm for NE GA and bordering upstate SC (even Augusta and Columbia would be a close call to a big deal) as depicted with 2-3” of snow, some sleet, and 0.5” of ZR with 0.8-0.9” qpf: 12Z GFS qpf:

12Z GFS 24 hour snow: significant increase over recent runs plus significant IP/ZR some areas

12Z Icon snow: