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Wintry Jan 15-16 Winter Storm Discussion & Obs

Interesting that GFS run was much warmer at the surface for clt. 29 and freezing rain and then climbs to 32 with the low passing to our south vs a much colder 12z run and sleet.
 
Excellent AFD from KATL:

Very complex fcst continues with much uncertainty and lack of
model consensus with possible snow/freezing rain event for
Saturday night through Sunday. The setup at least still looks to
have a strong 1030+ parent high advecting a classical CAD wedge
into the area by Saturday night, though models differ on how
low the upstream dewpts get and how cold the temps get within the
wedge. There is other variation in how far north or south the
upper cutoff wave and translated deepening sfc low are as well,
with the GFS looking to be a more northern solution and the Euro
being farther south. The southern solution would actually more
likely reinforce or strengthen the wedge as the gradient between
the low and the southern periphery of the wedge would be greater
and the more Miller Type A cyclogenesis could occur along a
stronger baroclinic zone. This could lead into a more significant
freezing rain potential. Thermal profiles still indicate that a
700-850mb warm nose will be advecting in against the wedge during
the day Sunday so have advertised what could be an onset of rain
to possible rain/snow mix Saturday night into more of a freezing
rain period mid Sunday morning into mid afternoon Sunday. The
system then looks to quickly swing into wrap-around CAA from the
north and west bringing more of a rain-to-snow transition. Given
the variation in progged snow and ice totals still in the
guidance, confidence is still rather low on amounts but we are
seeing the potential for some accumulating snow and freezing rain
near the Atlanta metro and along and north of I-20 corridor
eastward. If ice does accrete, the enhanced gusty gradient winds
would only increase the possible impact of downed
trees/powerlines. Also any snow/ice accumulations could have
lingering refreezing potential both Sunday night and Monday night.
Our forecast updates should hopefully increase in confidence in
the next 24-48 hrs once we get more of this resolved in some
short term hi-res guidance which should better capture the wedge
and various p-type extent.
 
BullCityWx said:
It’s amazing that the euro has a generational ice storm from Lexington to Camden but the GFS is like ????
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Ice is almost always over modeled 90% of the time for two reasons.
1. Temperatures are too marginal, and ice cannot accreate.
2. Models do a poor job with Ptype, and it ends up being sleet.

I definitely think #2 can be the this this time around if we’re looking at the same setup.
 
Not to be a debbie-downer but there appear to be BL issues on the happy hour goof for Atlanta - I'm talkin' ITP here- Temps start @ 84hrs at 45 & doesn't get below freezing until 105 when all the moisture is gone. 1-3" colors on the accumulation maps look nice, but with temps above 32, I don't imagine that much would accumulate.

Change my mind
 
Snownut said:
Exactly my thoughts watching this, is it's just not picking up on how cold it's gonna be

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It doesn’t matter how cold the surface is! It’s the 850 s and 925 layer! If any of those are above zero, then no snow! It can sleet and ZR with temps in the teens!
 
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NWMSGuy said:
Not sure how much further south that low will track but I would think any further south than what is being modeled folks in North Ms and Alabama may be in the sweet spot soon.

View attachment 104630
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Looking the 18z GFS, it really didn’t trend south by more than a smidge if that. It is quicker and transfers quicker though.
 
Ollie Williams said:
Ice is almost always over modeled 90% of the time for two reasons.
1. Temperatures are too marginal, and ice cannot accreate.
2. Models do a poor job with Ptype, and it ends up being sleet.

I definitely think #2 can be the this this time around if we’re looking at the same setup.
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Yeah, if you remember PDII and I think SuperCad in 2010, those were both storms where sleet saved the day. I think I-20 in SC is in trouble.
 
Showmeyourtds said:
Not to be a debbie-downer but there appear to be BL issues on the happy hour goof for Atlanta - I'm talkin' ITP here- Temps start @ 84hrs at 45 & doesn't get below freezing until 105 when all the moisture is gone. 1-3" colors on the accumulation maps look nice, but with temps above 32, I don't imagine that much would accumulate.

Change my mind
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In the GFS? You know it doesn't handle wedges well right?
 
Showmeyourtds said:
Not to be a debbie-downer but there appear to be BL issues on the happy hour goof for Atlanta - I'm talkin' ITP here- Temps start @ 84hrs at 45 & doesn't get below freezing until 105 when all the moisture is gone. 1-3" colors on the accumulation maps look nice, but with temps above 32, I don't imagine that much would accumulate.

Change my mind
Click to expand...
If the GFS truly is bad at CAD, then it'll be an outlier and we won't see temps that high. Let's get to Friday morning or tomorrow evening to find that out.
 
WxGSO said:
Remember, this is a serious CAD. The global models usually poorly model the CAD. I much prefer the NAM's temp profiles, so by tomorrow we should have a better handle.
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Just looking at extracted data for Saturday at 18z, the GFS has me at 38/31. The NAM has me at 32/2.

?
 
Showmeyourtds said:
Not to be a debbie-downer but there appear to be BL issues on the happy hour goof for Atlanta - I'm talkin' ITP here- Temps start @ 84hrs at 45 & doesn't get below freezing until 105 when all the moisture is gone. 1-3" colors on the accumulation maps look nice, but with temps above 32, I don't imagine that much would accumulate.

Change my mind
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I just saw accumulation last week at 35 when it was 80 the day before
 
I don't think you are going to see much in the way of major shifts in the models going forward. Granted, 50mi here or there can make a HUGE difference in terms of precip type for many. It's going to come down to how strong the CAD is and when the transfer of energy occurs.
 
Showmeyourtds said:
Not to be a debbie-downer but there appear to be BL issues on the happy hour goof for Atlanta - I'm talkin' ITP here- Temps start @ 84hrs at 45 & doesn't get below freezing until 105 when all the moisture is gone. 1-3" colors on the accumulation maps look nice, but with temps above 32, I don't imagine that much would accumulate.

Change my mind
Click to expand...

Easy. It’s botching the extent of the CAD. Unlike just about every other model.


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Tarheel1 said:
It doesn’t matter how cold the surface is! It’s the 850 s and 725 layer! If any of those are above zero, then no snow! It can sleet and ZR with temps in the teens!
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Yes but a colder CAD also limits how far north the LP can go north and will help really limit the warm nose coming up as far. It doesn’t play directly into the upper atmosphere temps but more do indirectly
 
Showmeyourtds said:
Not to be a debbie-downer but there appear to be BL issues on the happy hour goof for Atlanta - I'm talkin' ITP here- Temps start @ 84hrs at 45 & doesn't get below freezing until 105 when all the moisture is gone. 1-3" colors on the accumulation maps look nice, but with temps above 32, I don't imagine that much would accumulate.

Change my mind
Click to expand...

That would be great news for those that don’t want much ZR and bad news for those who want it. But I think it is too warm and that a significant ZR is more likely.
 
GaWx said:
I got you but don’t shoot the messenger ;)

Also, many wx fanatics want it whether they admit it or not. They always talk about the dreaded rain and 33 as being the worst thing, not the dreaded rain and 32 or 31.
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I'm one of those Wild Weather Mongers who adores ice. I despise sleet simply because what could have been a good snow is silly little ice pellets. If a tree falls on the house, a new roof comes in handy too. Of course, nothing beats a good coating of ice hidden under as many inches of snow as can fit! Oh, and I like canes too. Tornados, nope.
 
Can someone please post the GEFS precip type/mean map?
 
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