beanskip
Member
GSP/CLT back in the game if 18z NAM is, you know, sober.
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Wintry January 21-23 2025
- Thread starter SD
- Start date
WolfpackHomer91
Member
Same rule as earlier applies.... youd have to think its a bit more filled in than this but good way to start eve session
packfan98
Moderator
astroworld123
Member
we might be otw back ladies and gentlemen
Now we're cooking here midway between Atlanta and Athens:
Love it. Maybe FFC got an exclusive early showing
I’m proud of them for being different. Hope it pans out for them- don’t want to see them getting cooked online
Not sure on amounts (probably pretty light), but the snow is seemingly significantly further N/W across NC at hr 30. Returns showing back to the Triad, although will need to check more maps to see what’s reaching the ground…a better radar comparison in any case.
packfan98
Moderator
Yeah, the outline is there, but pretty anemic amounts this run. I expect it to fill in more over the next two model cycles
That was a big run. Really need that trend to keep going at 0z
Blue_Ridge_Escarpment
Member
you can see with the more NW movement how it drastically reduces the snow on the GA and SC beaches and 95 corridor. More mixing.
18z
12z
Orientation shift SW to NE and a big shift in impact area thru GA and Carolina even up to N. Metro a few more shifts like that are very possible and people could be getting some love further North while still deleivering goods to south
12z
Orientation shift SW to NE and a big shift in impact area thru GA and Carolina even up to N. Metro a few more shifts like that are very possible and people could be getting some love further North while still deleivering goods to south
That was a really good discussion....now we see why there is so much uncertainty with the models grasping the precip and expansive coverage to be much greater than modeled.
18z
12z
12z
Yeah, it’s hard to see getting more than an inch or so, even if this trends better. Wouldn’t hate seeing some snow on the ground with temperature below freezing all day on Wednesday, though. 1” is encroaching on Raleigh there on the 18z NAM.
Of course, with cold temps 1” will be more high impact on travel conditions than normal, should it happen. January 2005 harkens.
Area Forecast Discussion
National Weather Service Peachtree City GA
250 PM EST Mon Jan 20 2025
...Afternoon Area Forecast Discussion...
.SHORT TERM...
(This afternoon through Tuesday)
Issued at 247 PM EST Mon Jan 20 2025
Key Messages
- Winter storm warning issued for areas generally between Macon- Columbus south. Winter weather advisory to the north about to the I85 corridor.
- Light snow flurries could begin across central and parts of north GA as early as 9am on Tuesday.
- Temperatures in the upper teens with moderate winds may lead to windchills between 5 and 15 degrees. A Cold Weather Advisory has been issued for the entire WFO.
To keep things at a reasonable length, please refer to the previous AFD for a good analysis of the incoming winter weather potential. This AFD will cover changes/updates as well as concerns with model output going into the next 24-48 hours. With that, lets begin by addressing the limiting factors with this system.
The main point of concern can be condensed (*dum dum tsss*) down to the "where" and "how much" of moisture. Most models are in agreement
that over-riding moisture will be plentiful above 700mb. Significantly greater uncertainty exists at the 900-800mb level. Models have actually trended at a weakening of the dry layer at these lower levels (at least in recent runs). The 12z HREF sounding between Columbus-Macon and ATL being a great example of this (see Sunday 12z sounding at 1pm Tuesday and current 1pm Tuesday sounding). The controlling factor there is the strength of short/long lived southwesterly flow. The length of time over which SW flow occurs will be inversely proportional to the amount of sublimation. With all that said, there remains the potential that Hires guidance is under-representing the potential for snowfall as far north as the I20/I85 Corridor. One wonders if the ~1000ft less for the precip to fall to the surface may play assist snowfall to the surface.
Given this information, snowfall amounts have remained relatively unchanged if increased across the southern counties (see Winter
Storm Warning). This comes with a major Astrix. Should mid level moisture underperform areas in the advisory may very well see little to no snow (yay, less impacts!). Conversely, should moisture perform as discussed above, snowfall may very well likely overperform current forecast snow totals (yay, snow day!). Either way, it's going to be cold, as highs will likely struggle to get out of the
30s. Though this is also highly dependent on snowfall start time and when sfc temps reach the wetbulb (dry conditions mean Tw is well below freezing). Lows Tonight and Wednesday night will be frigid, with lows of 10 to 20 degrees and wind chills as low as the single digits.
National Weather Service Peachtree City GA
250 PM EST Mon Jan 20 2025
...Afternoon Area Forecast Discussion...
.SHORT TERM...
(This afternoon through Tuesday)
Issued at 247 PM EST Mon Jan 20 2025
Key Messages
- Winter storm warning issued for areas generally between Macon- Columbus south. Winter weather advisory to the north about to the I85 corridor.
- Light snow flurries could begin across central and parts of north GA as early as 9am on Tuesday.
- Temperatures in the upper teens with moderate winds may lead to windchills between 5 and 15 degrees. A Cold Weather Advisory has been issued for the entire WFO.
To keep things at a reasonable length, please refer to the previous AFD for a good analysis of the incoming winter weather potential. This AFD will cover changes/updates as well as concerns with model output going into the next 24-48 hours. With that, lets begin by addressing the limiting factors with this system.
The main point of concern can be condensed (*dum dum tsss*) down to the "where" and "how much" of moisture. Most models are in agreement
that over-riding moisture will be plentiful above 700mb. Significantly greater uncertainty exists at the 900-800mb level. Models have actually trended at a weakening of the dry layer at these lower levels (at least in recent runs). The 12z HREF sounding between Columbus-Macon and ATL being a great example of this (see Sunday 12z sounding at 1pm Tuesday and current 1pm Tuesday sounding). The controlling factor there is the strength of short/long lived southwesterly flow. The length of time over which SW flow occurs will be inversely proportional to the amount of sublimation. With all that said, there remains the potential that Hires guidance is under-representing the potential for snowfall as far north as the I20/I85 Corridor. One wonders if the ~1000ft less for the precip to fall to the surface may play assist snowfall to the surface.
Given this information, snowfall amounts have remained relatively unchanged if increased across the southern counties (see Winter
Storm Warning). This comes with a major Astrix. Should mid level moisture underperform areas in the advisory may very well see little to no snow (yay, less impacts!). Conversely, should moisture perform as discussed above, snowfall may very well likely overperform current forecast snow totals (yay, snow day!). Either way, it's going to be cold, as highs will likely struggle to get out of the
30s. Though this is also highly dependent on snowfall start time and when sfc temps reach the wetbulb (dry conditions mean Tw is well below freezing). Lows Tonight and Wednesday night will be frigid, with lows of 10 to 20 degrees and wind chills as low as the single digits.
Mahomeless
Member
It’s virga but it’s there, snowing at a few thousand feet
Need a miracle back west but nice trend for many the last 3 nam runs
Need that energy to dig more to move further south if we wanna see more forcing, we are getting there 
Pops
Member
No science here but still bet sn I w reaches I 20 from alabama through georgia..js
Robinssnow7
Member
Question... those nam totals... would that include virga or what it expects to reach the ground?
WolfpackHomer91
Member
Get the dews to be realistic and some virga yes.....but as I said earlier youd have to imagine this black box here is more full. Plus the Orientation still looks good.... keep it tilting and we can tap the faucet a tad I think
I truly love this hobby
Virga is factored in and taken out of QPF. Of course, FFC had some discussion that models could be overestimating how much precip will be lost to virga, as well, which could argue for more than what the models are showing, but that’s above my pay grade. Some of these DPs progged on the modeling do seem unrealistically low, though.
3K NAM with a little tick NW too. Interesting the northern cutoff is sharper than it's lower resolution cousin.
packfan98
Moderator
Definitely. Could be some heartbreak with mixing in coastal regions and Florida.
CAE raw off the 12z GFS:
Very cold 850s and .14 precip probably 1.5.-2 inches realized.
Code:
36 01/22 00Z 34 16 338 5 0.05 0.00 536 558 -8.8 -16.7 1028.4 100 -SN 045BKN112 120OVC228 251BKN355 37 34 20.0
42 01/22 06Z 28 22 38 10 0.09 0.00 536 558 -11.2 -16.5 1028.7 100 -SN 053BKN088 118OVC234 234OVC420 34 28 7.4Very cold 850s and .14 precip probably 1.5.-2 inches realized.
Robinssnow7
Member
Thank you.Virga is factored in and taken out of QPF. Of course, FFC had some discussion that models could be overestimating how much precip will be lost to virga, as well, which could argue for more than what the models are showing, but that’s sniff my pay grade. Some of these DPs progged on the modeling do seem unrealistically low, though.
bud006
Member
Just watched the briefing. I Thought Keith did a great job explaining and illustrating the concerns FFC has with the modeling, and the possibility of column saturation getting precip to the surface (especially metro and to the north) that the models have struggled to reflect.Love it. Maybe FFC got an exclusive early showing
I’m proud of them for being different. Hope it pans out for them- don’t want to see them getting cooked online
And right on cue, we see the latest NAM showing snow reaching the surface in the northern burbs.
What a fascinating close call this will be for a major metro area. I mentioned a couple days ago this very well may be a nowcasting scenario, and I’ve already told my wife if I call her tomorrow afternoon and tell her to leave her office, she needs to go.
—30—
Match the Kuchera ratios to the radar simulations for a quick analysis.
3K NAM did tick north - but it’s well south of the 12km- big time improvement for CAE area though 
packfan98
Moderator
Yeah, it will catch up a bit by the 12z run tomorrow, but you can bet it will be one of the driest models.
Makeitsnow
Member
NAM is finally understanding how to lift air parcels.
I am a few more tics away from legit business about 20 mile north of I 20 in West Georgia turn baby turn
beanskip
Member
Been waiting for the inevitable BL/temps issues in TLH -- no signs of it ... until 18z -- lost a degree or two from north Florida -- took away all my cushion! Who knows if it's right, of course.
ForsythSnow
Moderator
Honestly, what are the odds we see more of this and see the upper level DGZ produce and rip so much it completely blasts through the dry layer?
