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Wintry December 28-29th Possible Winter Storm

deltadog03 said:
As you know, as well as many, even if we only get a .25" of ZR it will be light enough that it can accumulate quickly.
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Great point, Chris. It isn't just the amounts. If it is spread out over longer periods, I'd think that the same amount of ZR would likely accumulate more

Meanwhile, I'm not sure if anyone mentioned this, but the 18Z German (ICON) has more WSW 500 mb flow than its prior runs, which seems to be leading to more qpf while still maintaining about as cold.
 
GeorgiaGirl said:
JMO, but this really isn't 2014 like imo with the danger that posed if any precip fell at all, yes it's been cold today but before the last day and a half to two as with 2014, it was sustained cold for much longer before the event happened...early Jan had the major cold snap for example. It won't be an everything falls sticks everywhere situation in the Deep South states I don't think...

There is a power danger though, as always with ice. Just think about it, if this is a bust low on QPF, man oh man.
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Thanks Georgia Girl. I didn't want to draw a correlation to January 2014 because it was substantially colder for longer before that event and if my comments was translated as much, I apologize.

I was thinking about the heavy wet snowstorm we had here earlier this month, when it was 70 degrees within 48 hours of the event starting. We're lucky if we sniff 45 tomorrow, then cloud cover Wednesday and precip Thursday-Friday morning.

The power danger is real, especially with our trees in such a distressed state given Irma and the heavy snow earlier this month. What trees didn't fall in those two events are vulnerable even with light ZR.

--30--
 
The extremely high 1km resolution Swiss model looks like it's going to be much further NW of most guidance w/ our storm. The end of the 18z run just beyond 72 hours has some snow/sleet in upstate SC all the way back to Greenville-Spartanburg lifting northward into NC. Unfortunately I can't get any other regions aside from NC or SC.... Curious to see how this model evolves over the course of the next day or so
Screen Shot 2017-12-25 at 5.08.20 PM.png
 
deltadog03 said:
As you know, as well as many, even if we only get a .25" of ZR it will be light enough that it can accumulate quickly.
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Also Chris, correct me if I'm wrong, but lighter QPF Rates will delay WAA from coming down to surface, in turn leading to a longer duration ZR event
 
Webberweather53 said:
The extremely high 1km resolution Swiss model looks like it's going to be much further NW of most guidance w/ our storm. The end of the 18z run just beyond 72 hours has some snow/sleet in upstate SC all the way back to Greenville-Spartanburg lifting northward into NC. Unfortunately I can't get any other regions aside from NC or SC.... Curious to see how this model evolves over the course of the next day or so
View attachment 2304
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Based on this as well as the more WSW H5 flow of the 18Z ICON, I do have to wonder if the common NW trends in the models will occur. If so, that could at least save SAV-CHS from getting a sig ZR since just a couple of degrees of warming could make the difference. Opinion?
 
GaWx said:
For GA: The 12Z GEFS mean is suggesting significant icestorm from near or just south of a line from Tony to GaGirl (N of this line may be mainly IP though lighter qpf) and then S of this to S/SW of MCN and then E to somewhat SW and S of SAV. For the areas in as well as S and SW of SAV, the QPF is about the heaviest, near 0.35", which would be at or near the most ZR for a storm since 1922.
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Yeah, sometimes the sleet band is only 30 miles wide. I can be in sleet and it's snowing at the airport, and zr in Barnesville. And light qpf can still cause lots of issues if it sticks from the onset. Hope I'm in the sleet zone, lol. I'm already maybe getting sleet tomorrow night, so Thurs is still up in the air as to how cold it gets. Love these set ups, but that waa can cause headaches and heartaches, lol.
 
dsaur said:
Yeah, sometimes the sleet band is only 30 miles wide. I can be in sleet and it's snowing at the airport, and zr in Barnesville. And light qpf can still cause lots of issues if it sticks from the onset. Hope I'm in the sleet zone, lol. I'm already maybe getting sleet tomorrow night, so Thurs is still up in the air as to how cold it gets. Love these set ups, but that waa can cause headaches and heartaches, lol.
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Heck I remember I think in about 1974, we had a system that gave Snow North of ATL, ZR/IP through Metro, and there were Tornado Watches out below Macon...
 
GaWx said:
Based on this as well as the more WSW H5 flow of the 18Z ICON, I do have to wonder if the common NW trends in the models will occur. If so, that could at least save SAV-CHS from getting a sig ZR since just a couple of degrees of warming could make the difference. Opinion?
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As partially discussed on another forum (I'll expand more here), what will have to happen to get this storm to come northwest & deliver a major winter storm to the southeastern US includes one or more of the following:...
1) Stronger disturbance in the southern branch. Vorticity grows exponentially in the presence of pre-existing vorticity and/or stretching, having a stronger system to work with from the beginning will pay massive dividends for our odds to see a major storm, and our chances will increase non-linearly (increasing more quickly as the s/w grows more intense & vis versa)
2) More stream separation between the southern and northern branch waves east of the Rockies. This allows the storm not to be northern stream dominant and entices more moist west-southwesterly flow aloft that can push precipitation deeper inland across the SE US instead of dry northwesterly flow with one consolidated wave in the northern branch of the jet.
3) More progressive trough over SE Canada. The faster it lifts out, the less confluence there is, thus our storm & parent s/w can intensify
4 (extra credit)) Slower trailing disturbance in the northern branch behind our s/w as it leaves the Rockies wouldn't hurt either, and would allow our s/w to undergo barotropic energy conversion more quickly (Barotropic energy conversion is another way of saying a trough tilted against the mean flow (negatively tilted south of the jet core in the N hem) grows at the expense of the jet, drawing momentum from it and converting background kinetic energy into eddies).

In comparison to other guidance, all 4 of these parameters are tilted more favorably for a big winter storm in the German (DWD-ICON) model which is why its solution is so extreme...

DWD-ICON
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UKMET
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CMC

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GFS
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Webberweather53 said:
The extremely high 1km resolution Swiss model looks like it's going to be much further NW of most guidance w/ our storm. The end of the 18z run just beyond 72 hours has some snow/sleet in upstate SC all the way back to Greenville-Spartanburg lifting northward into NC. Unfortunately I can't get any other regions aside from NC or SC.... Curious to see how this model evolves over the course of the next day or so
View attachment 2304
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Is it possible to post this same graphic but include the entire area instead of just NC?
 
JtSmarts said:
@Webberweather53 it also looks like that swiss model has the precip starting on Thursday morning. It seems like most of the models were indicating more of a Thurs evening/Friday morning deal.
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Yeah I noticed it was considerably faster, this is close to the truncation and a lot of the precipitation is near the edge of the domain, I'd like to see it move forward on the model and to the center of the domain. I'm actually not sure what its parent model is that provides the external boundary conditions which could have a pretty substantial effect on its forecast (for ex, the NAM is nested inside the GFS's global domain, if however the NAM was nested inside the CMC, ECMWF, or UKMET it would produce different solutions, especially closer to the edge of the NAM nest (like the Pacific NW, Caribbean, western Atlantic, etc. where it relies more on the parent model (the GFS).), nor am I currently aware of its biases but the model is very impressive in its own right to have a resolution of 1km and my experience with the model is that it's very solid esp in 48-60 hours, often completely obliterating the coarser 3km NAM & its WRF/NMMB cores, HRRR, & RGEM. For example, in the day preceding the early December winter storm, we had a morning w/ particularly low dew points that the HRRR, RGEM, & NAM completely botched, showing dews in the mid-upper 20s at best, we actually somehow got into the mid 10s which is where the super swiss HD had it. This is just one example, many of my meteorology friends at NC State could identify plenty more.
 
0z NAM is rolling, don't see any large changes yet out to 17 hours other than the surface high entering the northern Rockies and upper midwest looks a hair stronger
 
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