Christmas Storm VI

[Wild Weather Monger]

thanks. Well looking at the long water vapor loops and radar loops in Texas, it looks to me like the center of the vort isn't going to come off Houston, but more like enter into western Louisiana, a litle further north than most models are showing. This is going to be the "devil" in the details that makes or breaks a forecast i think. Also, its very good looking, and may be entering a neutral tilt stage soon. I wonder how much the convection is changing things there.

In the last few hours of animation it looks like the center has been pulled north more and is on a more easterly heading. I think I read the latent heat added something to the ambient air which allowed a new path on systems like this, so its going to be fun to follow.

You've been stressing for days now that the southern feature should hold together farther east than modeled. That certainly looks to be occurring. Kudos!

For N. Cental Ala. thru N. Central Ga. at least, I'll take my chances with this closed off over coastal La.

[Lookout]

Yeah, I was looking at that. 850's get ok, but I don't like that there is no help from the dp. Just need that northern stream sw to tuck and not over shoot. Get some good cold in here. T

It's going to be largely precipitation driven. What I mean by that is if you are under a decent enough area of precip for long enough, the column should drop to the wetbulb which should allow snow to reach the surface. But if the precip is lighter, it's probably going to be a mix of some kind. Even though the temps are above freezing, the lower dewpoints might allow sleet or snow to reach the surface.

Here is the 24 hour sounding for atlanta..notice the wetbulbs are near or below freezing. Even though the gfs shows a decent amount of precip, it doesn't drop the temps that much despite the wetbulbs. This is why I think it might not be handling the temps very well within these areas of heavier precip.

Date: 24 hour AVN valid 12Z SAT 25 DEC 10
Station: KATL
Latitude:   33.65
Longitude: -84.42
-------------------------------------------------------------------------------
LEV PRES  HGHT  TEMP  DEWP  RH  DD   WETB DIR SPD THETA THE-V THE-W THE-E   W
    mb     m     C     C    %   C     C  deg knt   K     K     K     K    g/kg
-------------------------------------------------------------------------------
 0 1000   141                                                                 
SFC  984   270   1.2  -3.0  74  4.2  -0.4 264   3 275.6 276.1 273.5 284.1  3.10
 2  950   557   3.4  -4.8  55  8.2   0.2 262   8 280.6 281.1 275.9 288.5  2.81
 3  900   994   1.6  -6.8  54  8.3  -1.6 260  13 283.1 283.5 276.9 290.4  2.55
 4  850  1453   1.5 -12.8  34 14.3  -3.3 251  19 287.7 288.0 278.0 292.7  1.68
 5  800  1941   0.9  -6.0  60  6.9  -1.9 246  26 292.1 292.6 281.8 301.1  3.04
 6  750  2459  -0.2  -1.0  95  0.7  -0.6 249  34 296.3 297.2 285.4 310.4  4.75
 7  700  3009  -2.5  -3.5  93  1.0  -2.9 252  38 299.7 300.5 286.2 312.5  4.22

[FoothillsNC]

Foothills. What are impacts on sensible weather if this low tracks through Louisiana? Does that imply a coastal low or OTS? If the northern stream digs more and the vort is more northerly, does that mean a phase is more or less likely?

I'd think the precip shield would end up futher north along with it. But with the tight northern stream ,it would only get so far, but under decent diffluence that will be across most of eastern Miss, Ala, and Ga at that time, the precip would probbably get very enhanced. Also by then the polar vort is progged to be incoming, and if the La storm is still in decent shape, I would expect it to begin to intensify and grow, deepen. But it depends on teh exact angle the vort coming in phases or not, and also, the tilt of the shortwave thats in La (or the Gulf) at that time. If its a very healthy wave, then it would probably get scooped northeast, and the snow would fly all across eastern Ala, Georgia and Carolnas. This isn't my forecast, but I won't be suprised if thats what ends up happening. Just keep watching trends.

[NorthernUpstateSC]

That's what i've been harping on for our area...it has consistently done bad with qpf up here as well, just give us the chance and think we'll be happy along and nw of the 85 corridor!

OconeeSC - I live in pickens county close to hwy. 11 not far from you at all and I agree about the qpf in our area consistently being under done. We have had alot more rain then gsp shows for the year so far and have constantly over performed on the qpf forecasts. The last good rain several weeks ago I think gsp has a little less then two inches, while we had over 5 inches. This storm is looking more and more promising and could turn out to be like the storms we used to have back in the 80's & 90's in our area.

[dsaur]

It's going to be largely precipitation driven. What I mean by that is if you are under a decent enough area of precip for long enough, the column should drop to the wetbulb which should allow snow to reach the surface. But if the precip is lighter, it's probably going to be a mix of some kind. Even though the temps are above freezing, the lower dewpoints might allow sleet or snow to reach the surface.

Here is the 24 hour sounding for atlanta..notice the wetbulbs are near or below freezing. Even though the gfs shows a decent amount of precip, it doesn't drop the temps that much despite the wetbulbs. This is why I think it might not be handling the temps very well within these areas of heavier precip.

Date: 24 hour AVN valid 12Z SAT 25 DEC 10
Station: KATL
Latitude:   33.65
Longitude: -84.42
-------------------------------------------------------------------------------
LEV PRES  HGHT  TEMP  DEWP  RH  DD   WETB DIR SPD THETA THE-V THE-W THE-E   W
	mb 	m 	C 	C    %   C 	C  deg knt   K 	K 	K 	K    g/kg
-------------------------------------------------------------------------------
 0 1000   141                                                             	
SFC  984   270   1.2  -3.0  74  4.2  -0.4 264   3 275.6 276.1 273.5 284.1  3.10
 2  950   557   3.4  -4.8  55  8.2   0.2 262   8 280.6 281.1 275.9 288.5  2.81
 3  900   994   1.6  -6.8  54  8.3  -1.6 260  13 283.1 283.5 276.9 290.4  2.55
 4  850  1453   1.5 -12.8  34 14.3  -3.3 251  19 287.7 288.0 278.0 292.7  1.68
 5  800  1941   0.9  -6.0  60  6.9  -1.9 246  26 292.1 292.6 281.8 301.1  3.04
 6  750  2459  -0.2  -1.0  95  0.7  -0.6 249  34 296.3 297.2 285.4 310.4  4.75
 7  700  3009  -2.5  -3.5  93  1.0  -2.9 252  38 299.7 300.5 286.2 312.5  4.22

I hope and think you are right! I have been with the doc for it's consistancy, and can't find myself trusting the gfs's view on temps.

Anyway, it will be nearing dusk, and we should be getting at least some cooling virga early on. I'm glad this seems to have decided to come in in the evening instead of 12zish. T

[Brick Tamland]

Who would have thought the GFS would be the one to come around at the end and give us the most precip.

[Brian]

Who would have thought the GFS would be the one to come around at the end and give us the most precip.

It usually does at the very end, does anyone think that WSW's will be issued later????

[downeastnc]

So we really need that 12Z GFS to be right huh.....looking at the RUC and how the southern stream is doing I cant say I see why it wouldnt be right or at least more so than the NAM or the 6Z GFS. Oh well getting to the point were whats happening now tells us morethan the models anyhow....hopefully the 12Z GFS is right gonna be awesome to see some flakes on XMAS for the first time here in my 38yrs.

[buckeyefan1]

CAE as of 1:07...lol

.SHORT TERM /SATURDAY THROUGH SUNDAY/...

CONFIDENCE NOW HIGH FOR MAINLY A RAIN EVENT ACROSS THE MIDLANDS OF

SOUTH CAROLINA AND EAST CENTRAL GEORGIA...

MODELS NOW IN GOOD AGREEMENT. UPPER TROUGH OVER THE UPPER

MIDWEST/GREAT LAKES...WILL REMAIN POSITIVELY TILTED AS IT TRACKS

EAST-SOUTHEAST ACROSS KENTUCKY/CAROLINAS THROUGH SUNDAY. SHORT

WAVE OVER THE SOUTHERN PLAINS WILL CONTINUE TO TRACK SOUTHEAST

ALONG THE NORTHERN GULF OF MEXICO SATURDAY...AND TRIGGER WEAK

SURFACE CYCLOGENESIS. THE MODEL CONSENSUS SURFACE LOW PRESSURE TRACK

IS EAST-NORTHEAST ACROSS NORTHERN FLORIDA AND RAPIDLY NORTHEAST OF THE

CAROLINA COAST...TOO FAR NORTH AND FAST FOR SIGNIFICANT SNOWFALL

FOR THE MIDLANDS. THE MUCH STRONGER SURFACE CYCLOGENESIS WILL

OCCUR ALONG THE MID ATLANTIC COASTLINE LATER ON SUNDAY AS SYSTEM

PHASES WITH UPPER LEVEL TROUGH.

MODEL SOUNDINGS SUPPORT MORE RAIN THAN SNOW WITH IMMEDIATE

SURFACE LAYERS MAINLY ABOVE ZERO. PARTIAL THICKNESSES AND MODELS

SOUNDINGS SUPPORT HIGHER CHANCE SNOW NORTH AND WEST OF COLUMBIA

LATE SATURDAY AND SATURDAY NIGHT. STRONGEST SYNOPTIC LIFT SATURDAY

EVENING AS UPPER LEVEL DIVERGENCE INCREASES AHEAD OF APPROACHING

SHORT WAVE TROUGH IN WESTERN GEORGIA. AS 850MB LOW MOVES OFFSHORE

EARLY SUNDAY COLD ADVECTION DEVELOPS AND SOUNDINGS SUPPORT SNOW

FLURRIES/OR FREEZING DRIZZLE ACROSS THE REGION AS MOISTURE BECOMES MORE

SHALLOW DURING THE DAY. ANY SNOW ACCUMULATION WILL REMAIN ACROSS

THE NORTH MIDLANDS/PEE DEE AND WILL LIKELY BE QUITE LIGHT. LITTLE

OR NO ACCUMULATION EXPECTED FROM THE CENTRAL MIDLANDS TO THE

CENTRAL SAVANNAH RIVER AREA. HIGH TEMPERATURES SATURDAY RANGING

FROM THE UPPER 30S NORTH TO NEAR 50 SOUTH. LOW SATURDAY NIGHT

CLOSE TO CONSENSUS IN THE UPPER 20S TO MID 30S. HIGHS SUNDAY ONLY

IN THE UPPER 30S TO LOWER 40S.

[Itunis]

It usually does at the very end, does anyone think that WSW's will be issued later????

I posted this in the banter thread, I personally doubt WSWs at this time. The GFS/Euro both show better qpf, but temps are still an issue and would prevent most in N GA from getting more than 2" or so. Not to mention the initialization errors. I personally think advisories for far N GA will be initiated later this evening as temps support mostly snow there, though QPF is a little lacking.

[NEGa]

I posted this in the banter thread, I personally doubt WSWs at this time. The GFS/Euro both show better qpf, but temps are still an issue and would prevent most in N GA from getting more than 2" or so. Not to mention the initialization errors. I personally think advisories for far N GA will be initiated later this evening as temps support mostly snow there, though QPF is a little lacking.

i would agree, cant see wsw being posted with the afternoon updates. they might do advisories for farther north, but even that is iffy at this point. i just wish the 18z would give some consistency and at least shed a little light on the storm that is coming in TONIGHT lol

[Stormsfury]

Honestly, this is the prime reason many snowstorms in the Southeast and points north are so hard to forecast and the reason why some of the past events have been so poorly forecast. Even with today's technology in our hands, it's a mass confusion amongst the major guidance.

Literally, how this thing unfolds is in a sense, like baseball, a game of inches. a little this way, you have very little, a little that way, boom dynamite. I mean, how everything is coming together is like a World Series and you have Hank Aaron, or Babe Ruth at the plate facing Cy Young. We just don't know which is going to the better player just yet.

[NEGa]

Honestly, this is the prime reason many snowstorms in the Southeast and points north are so hard to forecast and the reason why some of the past events have been so poorly forecast. Even with today's technology in our hands, it's a mass confusion amongst the major guidance.

Literally, how this thing unfolds is in a sense, like baseball, a game of inches. a little this way, you have very little, a little that way, boom dynamite. I mean, how everything is coming together is like a World Series and you have Hank Aaron, or Babe Ruth at the plate facing Cy Young. We just don't know which is going to the better player just yet.

i really wouldnt want to be a met in the se right now..i mean what do you do? no consensus, and its such a close call and this is the kind of bust remembered a long time, either way. play it safe, just mention some snow and when there is a white christmas everyone is happy. if the 18z are wet and the mets honk on a white christmas in the se and we get nothing, well that will be in everyone's memory a long time (and not just little kids lol). its a total catch 22

was pretty excited at the 12z runs until i saw the error message. so i guess its down to the 18z and maybe 00z and then thats it, total now cast time (finally)

[dsaur]

Honestly, this is the prime reason many snowstorms in the Southeast and points north are so hard to forecast and the reason why some of the past events have been so poorly forecast. Even with today's technology in our hands, it's a mass confusion amongst the major guidance.

Literally, how this thing unfolds is in a sense, like baseball, a game of inches. a little this way, you have very little, a little that way, boom dynamite. I mean, how everything is coming together is like a World Series and you have Hank Aaron, or Babe Ruth at the plate facing Cy Young. We just don't know which is going to the better player just yet.

I wish that satellite was centered directly overhead on the vapor loop. Trying to gage the horses positions at this oblique angle is difficult, and it seems that it will be coming down to a photo finish. T

[phil882]

Honestly, I think the bigger player at work here is the seemingly insignificant northern stream short-wave that was poorly modeled yesterday by the gfs. Now that it is becoming more obvious that it is a discrete feature, it might have some pretty significant short term implications. Let me explain below.

Lets forget about the southern stream shortwave for a second and just focus on the northern stream feature that looks to be causing the bulk of the phasing now. Just take a comparison of the both the 18z gfs and the 06z gfs compaired with the wetter runs of the 00z gfs and the 12z gfs...

If you notice when this shortwave was depicted as weaker and almost non existent, the low off the SC/NC coast was significantly weaker, and the finger of moisture into the piedmont of NC/SC was also weaker. However, both the 00z runs, and especially the 12z run show a stronger shortwave feature in the northern stream, which seems to promote an earlier and stronger phase that allows more precipitation to occur across the southeast.

Now lets take a look at the latest analysis from the RUC to see which run is verifying the best.

The RUC seems to indicate a more potent northern stream shortwave than even the 12z gfs was indicating. Thus, I think the wetter and more amplified solutions of the 12z and 00z gfs are more likely to verify. In fact, if the 18z RUC is correct, it seems that these solutions might not be amplified enough!

[Rankin5150]

Dang...I have been so focused on track, QPF and phasing that I have lost a little bit of sight on the Temperature aspect of things. NWS-GSP shows my area (Charlotte back to Shelby in Rain/Snow mix tomorrow afternoon, at the height of the storm. Sheesh... I guess I need to look at thickness profiles, unless someone wants to calm my weenism down...

[NEGa]

Honestly, I think the bigger player at work here is the seemingly insignificant northern stream short-wave that was poorly modeled yesterday by the gfs. Now that it is becoming more obvious that it is a discrete feature, it might have some pretty significant short term implications. Let me explain below.

thank you for the great write up and explanation. that makes perfect sense, and i am always amazed at how great people are here at finding these small interactions that operate like the 'butterfly' affect further upstream. this is a great explanation. . . visual aids are always effective!

[eyewall]

Alright I made an update of my accums and forecast along with a new discussion:

http://www.sandhillswx.com/

[HKY_WX]

Honestly, I think the bigger player at work here is the seemingly insignificant northern stream short-wave that was poorly modeled yesterday by the gfs. Now that it is becoming more obvious that it is a discrete feature, it might have some pretty significant short term implications. Let me explain below.

Lets forget about the southern stream shortwave for a second and just focus on the northern stream feature that looks to be causing the bulk of the phasing now. Just take a comparison of the both the 18z gfs and the 06z gfs compaired with the wetter runs of the 00z gfs and the 12z gfs...

If you notice when this shortwave was depicted as weaker and almost non existent, the low off the SC/NC coast was significantly weaker, and the finger of moisture into the piedmont of NC/SC was also weaker. However, both the 00z runs, and especially the 12z run show a stronger shortwave feature in the northern stream, which seems to promote an earlier and stronger phase that allows more precipitation to occur across the southeast.

Now lets take a look at the latest analysis from the RUC to see which run is verifying the best.

The RUC seems to indicate a more potent northern stream shortwave than even the 12z gfs was indicating. Thus, I think the wetter and more amplified solutions of the 12z and 00z gfs are more likely to verify. In fact, if the 18z RUC is correct, it seems that these solutions might not be amplified enough!

yep the 18z ruc is continuing the trend of weakening the lead PJ wave and strengthening the one over the western dakotas that is diving south. if that continues, it will result in even less shearing of the stj wave and increasing the chance of a phase as the northern jet comes in behind it.

[Stormsfury]

i really wouldnt want to be a met in the se right now..i mean what do you do? no consensus, and its such a close call and this is the kind of bust remembered a long time, either way. play it safe, just mention some snow and when there is a white christmas everyone is happy. if the 18z are wet and the mets honk on a white christmas in the se and we get nothing, well that will be in everyone's memory a long time (and not just little kids lol). its a total catch 22

was pretty excited at the 12z runs until i saw the error message. so i guess its down to the 18z and maybe 00z and then thats it, total now cast time (finally)

I think KCHS is playing it the best. KCAE's earlier discussion was obviously uncoordinated with KCHS. I still think it's obvious, there's snow to be had, but the biggest question is just how much and with a severe spread of solutions with just subtle differences, there's just no way to confidently say, this or that's going to happen.

This system is nowhere near like the Feb 12th storm where my confidence was at an all-time high.

[NEGa]

I think KCHS is playing it the best. KCAE's earlier discussion was obviously uncoordinated with KCHS. I still think it's obvious, there's snow to be had, but the biggest question is just how much and with a severe spread of solutions with just subtle differences, there's just no way to confidently say, this or that's going to happen.

This system is nowhere near like the Feb 12th storm where my confidence was at an all-time high.

safe is the way to go, esp at this time of year. i was really hoping to at least have a better idea by now, but i may not be able to make any plans for tomorrow until tonight

[FoothillsNC]

yep the 18z ruc is continuing the trend of weakening the lead PJ wave and strengthening the one over the western dakotas that is diving south. if that continues, it will result in even less shearing of the stj wave and increasing the chance of a phase as the northern jet comes in behind it.

my fear is that the Tx wave won't get out ahead of it in time. Its so close. But the trends on RUC are good. I'd also like to see alittle more ridging ahead of the Tex wave when its nearing the gulf coast about 18 hours. Theres no doub the southern trough goes neg. tilt right at the end there, weakens a little but good structure. If everything comes together absolutely perfectly , this would be quite an intense snowstorm, with high snowfall rates, but thats one humongous big IF. And usually hard to get.

[kanc2001]

I think KCHS is playing it the best. KCAE's earlier discussion was obviously uncoordinated with KCHS. I still think it's obvious, there's snow to be had, but the biggest question is just how much and with a severe spread of solutions with just subtle differences, there's just no way to confidently say, this or that's going to happen.

This system is nowhere near like the Feb 12th storm where my confidence was at an all-time high.

CAE is obviously being conservative, guess they figure if the bust and snows its way better than if they forecast accumulating snow and there is nothing. Have noticed their lack of coordination with CHS. seems like they have a better relationship with GSP as they have to introduced boundery layer issues in their zones...

[phil882]

thank you for the great write up and explanation. that makes perfect sense, and i am always amazed at how great people are here at finding these small interactions that operate like the 'butterfly' affect further upstream. this is a great explanation. . . visual aids are always effective!

Thanks! It really does go to show how just small changes to tiny features in meteorology can have significant even major implications to a forecast. This is especially true with regards to phasing since energy transfer is a very delicate thing. You can have all the available potential energy in the world, but if you don't have the features work out just right, you don't get the most efficient energy transfer and thus there is not as much kinetic energy produced to get your snowstorm. Specifically with this event, I think the northern stream is going to drive what occurs in the next 24-48 hours. The southern stream feature is nice to add energy (through latent heat), but it still looks to get squashed before it really can cause any meaningful dip in the upper level heights. Thus, its up to this northern stream feature is dip down far enough south to tap into the positive vorticity advection that this southern stream shortwave is producing.

[WXinCanton]

I posted this in the banter thread, I personally doubt WSWs at this time. The GFS/Euro both show better qpf, but temps are still an issue and would prevent most in N GA from getting more than 2" or so. Not to mention the initialization errors. I personally think advisories for far N GA will be initiated later this evening as temps support mostly snow there, though QPF is a little lacking.

I agree! Happens with every event some people get so hell bent on why we dont have WSW or warning. Folks WSW don't make it snow, I think we found that out last year

[Carvers Gap]

I'd think the precip shield would end up futher north along with it. But with the tight northern stream ,it would only get so far, but under decent diffluence that will be across most of eastern Miss, Ala, and Ga at that time, the precip would probbably get very enhanced. Also by then the polar vort is progged to be incoming, and if the La storm is still in decent shape, I would expect it to begin to intensify and grow, deepen. But it depends on teh exact angle the vort coming in phases or not, and also, the tilt of the shortwave thats in La (or the Gulf) at that time. If its a very healthy wave, then it would probably get scooped northeast, and the snow would fly all across eastern Ala, Georgia and Carolnas. This isn't my forecast, but I won't be suprised if thats what ends up happening. Just keep watching trends.

Honestly, I have no idea where these posts are going. I posted this once. Mods send me an IM if their is a problem. Thanks for the discussion, Foothills. I agree this is going to be a tight fit if it is going to phase. Merry Christmas and thanks for the response. The RUC has been interesting the last few runs.

[Lookout]

I hope and think you are right! I have been with the doc for it's consistancy, and can't find myself trusting the gfs's view on temps.

Anyway, it will be nearing dusk, and we should be getting at least some cooling virga early on. I'm glad this seems to have decided to come in in the evening instead of 12zish. T

I hope so too lol. Hopefully we can get enough precip early enough to prevent much warming tomorrow. This is one of the rare times it looks to start early in the morning. If this started in the afternoon, we would warm up too much.

I posted this in the banter thread, I personally doubt WSWs at this time. The GFS/Euro both show better qpf, but temps are still an issue and would prevent most in N GA from getting more than 2" or so. Not to mention the initialization errors. I personally think advisories for far N GA will be initiated later this evening as temps support mostly snow there, though QPF is a little lacking.

I agree. I'd be surprised if anyone gets 2 inches outside the mountains in north georgia. I think the best anyone can hope for is an inch. It probably will only occur in rather narrow/small areas with everyone else getting a dusting to half inch or less. Mainly because of marginal surface temps combined with the fact this is falling in the daytime so you have solar insolation keeping ground temps warm enough to melt a good portion of whatever falls. The gfs/nam don't show a lot falling after dark unfortunately.

Of course this is assuming the models are handling things right. Obviously if such scenarios robert and others have mentioned happened, we would be looking at something a lot more interesting.

Here is the current ground temps

[eyewall]

[eyewall]

I agree! Happens with every event some people get so hell bent on why we dont have WSW or warning. Folks WSW don't make it snow, I think we found that out last year

A classic example of this is the Sanford Meso Band last year. Advisory there but no warning and they got pummeled.

[HKY_WX]

my fear is that the Tx wave won't get out ahead of it in time. Its so close. But the trends on RUC are good. I'd also like to see alittle more ridging ahead of the Tex wave when its nearing the gulf coast about 18 hours. Theres no doub the southern trough goes neg. tilt right at the end there, weakens a little but good structure. If everything comes together absolutely perfectly , this would be quite an intense snowstorm, with high snowfall rates, but thats one humongous big IF. And usually hard to get.

Yea, the southern vort needs to move a little quicker. The ruc kinda does that. We'll see what happens.