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Wintry ❄The Christmas Miracle❄(12-24/12-25)

Jon said:
So by get the job done I’m still confused with what we’re taking about here. Flurries or are you saying epic convective snow bursts with decent to heavy rates? Sounds like you’re kinda bullish here. If you were to forecast the event, what’s the most likely outcome?
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What I’m actually saying is that your concerns about low level dry air on the HRRR are unfounded based on my last few responses to you. 60% RH in a convective environment is not that big of a deal esp when your dry layer is only just over a few thousand feet thick
 
Jon said:
So by get the job done I’m still confused with what we’re taking about here. Flurries or are you saying epic convective snow bursts with decent to heavy rates? Sounds like you’re kinda bullish here. If you were to forecast the event, what’s the most likely outcome?
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Most likely outcome, if/where it snows it’s probably not going to be just some flurries. Near Absolutely unstable soundings/steep low level lapse rates with saturated DGZ, that’s a highly convective environment. Thus, if it snows, it will come down pretty hard imo based on that and we will have mini snow squalls where precip is legitimately falling. The low levels become unsaturated with the heating of the day and without it we won’t be unstable enough to generate precip
 
Webberweather53 said:
Most likely outcome, if/where it snows it’s probably not going to be just some flurries. Near Absolutely unstable soundings/steep low level lapse rates with saturated DGZ, that’s a highly convective environment. Thus, if it snows, it will come down pretty hard imo based on that and we will have mini snow squalls where precip is legitimately falling. The low levels become unsaturated with the heating of the day and without it we won’t be unstable enough to generate precip
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Ok cool. Thanks! It makes sense given the Omega and saturation at DGZ and the connective nature.
 
Webberweather53 said:
What I’m actually saying is that your concerns about low level dry air on the HRRR are unfounded based on my last few responses to you. 60% RH in a convective environment is not that big of a deal esp when your dry layer is only just over a few thousand feet thick
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So no virga and instant snow bursts. We’ll see!
 
Jon said:
If there’s any virga whatsoever than my concern about a dry layer isn’t “unfounded”
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No need to get snarky and have an attitude here because I disagree with you. Your concern is based on the HRRR sounding you were gawking over last night and that dry layer wasn’t that strong or very deep at all, unless you can convince me that a 3-4K feet dry layer with 80% RH is substantial I don’t see your argument. Anyway carry on.
 
malak05 said:
What some models are showing for the backside snow as main line passes thru GA around 2-3 PM there is some moisture kick-in that fills in from SW/NE along back of line and it appears that would be what has potential to changeover in the afternoon hours.
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It looks like as the trough goes neutral, another small piece of energy gets injected into main energy of the upper level trough which allows some moisture to redevelop on the backside of the band. That being said, NWS just put out a tweet saying the line is moving 1-2 hours faster than their modeling so that may not bold well for any chance of snow on the backside of the band.
 
So what does this front moving faster than anticipated mean for the snow in Georgia and/or possibility of convective snow east of the mountains?
 
Webberweather53 said:
No need to get snarky and have an attitude here because I disagree with you. Your concern is based on the HRRR sounding you were gawking over last night and that dry layer wasn’t that strong or very deep at all, unless you can convince me that a 3-4K feet dry layer with 80% RH is substantial I don’t see your argument. Anyway carry on.
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I don’t recall saying substantial, maybe I did, but it’s there nonetheless. My point was to keep expectations low. You aren’t exactly the nicest with wording on here, (and maybe that’s 100% unintentional on your part and it’s how I take it), but thanks for your input. I do appreciate you answering my questions.
 
By 0z this evening, with corroborating radar and sounding data from the TN Valley directly underneath the upper level low, I think we'll have a really good gauge on which camp is going to win out tomorrow east of the mountains in the Carolinas. The drier/shallower mixed layer ARW, NSSL, & NAM cores vs the moist/deeper mixed layer HRRR.

The differences between the two models are already fairly noticeable even by hr 10.



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Sleet City USA said:
So what does this front moving faster than anticipated mean for the snow in Georgia and/or possibility of convective snow east of the mountains?
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It really only affects GA and it's potential for backend snow on the main band coming through our area right now. Doesn't really affect the snow flurry/shower potential afterwards.
 
Jon said:
I don’t recall saying substantial, maybe I did, but it’s there nonetheless. My point was to keep expectations low. You aren’t exactly the nicest with wording on here, (and maybe that’s 100% unintentional on your part and it’s how I take it), but thanks for your input. I do appreciate you answering my questions.
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Well it was definitely substantial enough that you were legitimately concerned about it preventing snow in many locations and made a post about here and on twitter, so I'd definitely consider it a substantial/significant concern no?

 
This event on Nov 30th in the St Louis metro area probably isn't a bad, conservative analog to what we'll see tomorrow in the Carolinas (& most NWP models never forecasted even so much as a flurry in their forecast fields, most places saw at least flurries.), although this trough and associated cyclonic vorticity advection is much, much stronger this time around than it was for STL on Nov 30. Both of these generally argue for better coverage of precipitation and higher rates where precipitation occurs tomorrow in the Carolinas vs in STL on Nov 30 imo.

Nov 30 event
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Tomorrow
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Webberweather53 said:
This event on Nov 30th in the St Louis metro area probably isn't a bad, conservative analog to what we'll see tomorrow in the Carolinas (& most NWP models never forecasted even so much as a flurry in their forecast fields, most places saw at least flurries.), although this trough and associated cyclonic vorticity advection is much, much stronger this time around than it was for STL on Nov 30. Both of these generally argue for better coverage of precipitation and higher rates where precipitation occurs tomorrow in the Carolinas vs in STL on Nov 30 imo.

Nov 30 event
View attachment 59867


Tomorrow
View attachment 59869
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I still Managed a light rain snow mix with that November 29th trough to ?
 
Webberweather53 said:
The lower levels aren’t dry though in that sounding, if you looked at the corresponding sounding from pivotal weather, the lower level relative humidity is still greater than 80%, with a sub saturated layer that’s only 3000-4000 feet deep verbatim on the HRRR, that’s a pretty negligible dry layer if you ask me. Yes saturation with respect to ice is an additional percent or two lower than water which gives additional one or two RH percentage points in a sub freezing environment. If the HRRR came to fruition there wouldn’t be any concerns with dry air imo based on that sounding you showed. Oth, other models like the NSSL, ARW, & NAM are drier with a shallower mixed layer and they do look more concerning in that regard and I think the HRRR may be over mixing the BL which is causing it to produce more precip than the other cams. For ex: Simply mixing two relatively moist but unsaturated parcels leads to supersaturation because the mixing occurs linearly while saturation vapor pressure is exponential. Excess boundary layer mixing begets saturation and forcing for ascent
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So in other words the HRRR is trolling us.


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For foothills people ive noticed the 3K NAM has increased total for areas along and east of the blue ridge even has a three inch area at my house. The hrrr is also starting to trend in that direction also. its currently 43.8 here so well see....good luck fellas
 
LovingGulfLows said:
It looks like as the trough goes neutral, another small piece of energy gets injected into main energy of the upper level trough which allows some moisture to redevelop on the backside of the band. That being said, NWS just put out a tweet saying the line is moving 1-2 hours faster than their modeling so that may not bold well for any chance of snow on the backside of the band.
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Looks like that may be happening with the line developing on the east side of BHM.

D8B5F3A5-C996-423D-BC73-F67661EAB2FA.jpeg
 
FallsLake said:
Many years back, we had some convective snow bands come through the day after a storm. It was very impressive. It would darken up, snow (big flakes) for 20 minutes, stop, and then the sun would come out. It did this three or four times.
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Yeap I was at NCSU at the time around 96 or so.


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HSV AFD update at 0950
“
The depth of moisture appreciable increases between 700 mb and 850
mb in most guidance late this afternoon into the evening hours. This
combined with forcing along and ahead of the quick moving secondary
cold front and some fairly steep low level lapse rates this evening
should allow for some scattered snow shower development this evening.
Given the west northwest orientation of the low level winds ahead of
the front, some very minor lake enhanced snow bands look possible
from portions of Morgan county into the Lake Guntersville area,
primarily east of the I-65 corridor. If these occur some local
accumulations around one half of an inch could occur. Road
temperatures should remain warm enough to keep any accumulations
mainly on grassy surfaces. Will be evaluating any possible advisory
criteria in the afternoon forecast package, but at this time impacts
do not look widespread enough for one yet.”
 
WSB in house radar says nada. Of course it may be bunk. Hard to believe with how quick it’s moving for there to be changeover unless we see substantive redevelopment over the west and some reports that we actually have some pingers.


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JHS said:
GSP hinted in their latest discussion that small pops might be needed east of the mountains for tomorrow.
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Im def interested in there next update especially the implications of the precip stalling/slowing down this evening. The wienie in me wants the precip to hang around longer to get the cold air to catch up....
 
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