Winter Speculation 17/18 -December Thread

[Carvers Gap]

From MRX this afternoon....

LONG TERM (Tuesday night through Sunday)...A cold front will be exiting to the east to start the long-term period of the forecast Tuesday Night. Showers will come to an end from west to east. There is some question around will there be enough moisture leftover Tuesday night for a few snow shower/flurries in the mountain. For now, have continued with a slight chance of a rain/snow mix but latest models are rather progressive and depict the precipitation exiting by 06z Wednesday. The main story for the long term will be the persistent intrusion of arctic air into the area. The highly amplified pattern remains fixed throughout the long-term forecast period with a deep trough across the Eastern Conus and a ridge across the Western CONUS. The first shot of cold air will arrive Wednesday behind the initial front as the upper level pattern begins to amplify. Partly to mostly sunny skies are forecast in the dry airmass with PW values in the 0.2-0.3 inch range. High temperatures will only top out in the 40s across most valley locations. Another shot of cold air will arrive with a dry frontal passage late Wednesday night into Thursday as a upper level trough dives south out of Canada into the Ohio River Valley. High temperatures once again on Thursday will top out in the upper 30s to 40s. Another shortwave trough will dig further southward on Friday into Tennessee River Valley with 850 mb temperatures crashing into the - 10 to -8 degrees Celsius range. These values are two standard deviations colder than normal. The airmass remains dry but there could be enough lift with the trough diving further southward for a few flurries or light snow showers on Friday. Temperatures will warm into the upper 30s and lower 40s so any light precip would transition to the liquid form for most locations Friday afternoon. The best chance for precipitation during the cold blast will come on Saturday as yet again another shortwave trough rounds the base of the longwave trough. This clipper system will move into the area on Saturday with light snow shower/flurries possible. Moisture remains limited and do not expect any significant accumulations. Will not mention anything in the HWO at this time but will continue to monitor trends throughout the week. This system will bring in yet again another shot of cold air with 850 mb temperatures down into the -15 to -10 degrees Celsius range. The coldest days of the forecast period will be Friday and Saturday with highs only in the upper 30s to low 40s. The coldest morning will be Sunday with lows in the upper teen to low 20s. Temperatures will moderate some on Monday but remain a few degrees below normal. Models beyond the long-term period suggest that the cold arctic air intrusion will continue well into next week.

[PowellVolz]

From MRX this afternoon....

LONG TERM (Tuesday night through Sunday)...A cold front will be exiting to the east to start the long-term period of the forecast Tuesday Night. Showers will come to an end from west to east. There is some question around will there be enough moisture leftover Tuesday night for a few snow shower/flurries in the mountain. For now, have continued with a slight chance of a rain/snow mix but latest models are rather progressive and depict the precipitation exiting by 06z Wednesday. The main story for the long term will be the persistent intrusion of arctic air into the area. The highly amplified pattern remains fixed throughout the long-term forecast period with a deep trough across the Eastern Conus and a ridge across the Western CONUS. The first shot of cold air will arrive Wednesday behind the initial front as the upper level pattern begins to amplify. Partly to mostly sunny skies are forecast in the dry airmass with PW values in the 0.2-0.3 inch range. High temperatures will only top out in the 40s across most valley locations. Another shot of cold air will arrive with a dry frontal passage late Wednesday night into Thursday as a upper level trough dives south out of Canada into the Ohio River Valley. High temperatures once again on Thursday will top out in the upper 30s to 40s. Another shortwave trough will dig further southward on Friday into Tennessee River Valley with 850 mb temperatures crashing into the - 10 to -8 degrees Celsius range. These values are two standard deviations colder than normal. The airmass remains dry but there could be enough lift with the trough diving further southward for a few flurries or light snow showers on Friday. Temperatures will warm into the upper 30s and lower 40s so any light precip would transition to the liquid form for most locations Friday afternoon. The best chance for precipitation during the cold blast will come on Saturday as yet again another shortwave trough rounds the base of the longwave trough. This clipper system will move into the area on Saturday with light snow shower/flurries possible. Moisture remains limited and do not expect any significant accumulations. Will not mention anything in the HWO at this time but will continue to monitor trends throughout the week. This system will bring in yet again another shot of cold air with 850 mb temperatures down into the -15 to -10 degrees Celsius range. The coldest days of the forecast period will be Friday and Saturday with highs only in the upper 30s to low 40s. The coldest morning will be Sunday with lows in the upper teen to low 20s. Temperatures will moderate some on Monday but remain a few degrees below normal. Models beyond the long-term period suggest that the cold arctic air intrusion will continue well into next week.

Yeah MRX is meh as usual. They don’t get excited easily.


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[Carvers Gap]

The 0z EPS shows one of the potential pitfalls of the pattern as does the 0z GES.  The ridge builds in from the West late in wk 2....maybe a Chinook that builds some heat over the lee of the Rockies, and then the heat spreads eastward?  A sprawling PNA ridge with a weak NAO.... To me, it casts some doubt on how long the pattern can last in the upper south, especially the further west one goes.  Looks like the pattern lasts at least a couple of weeks(does that count as a pattern?)

[Carvers Gap]

12z NAM goes west again w the weekend system. Low in the Lakes will cause problems IMO.

[nrgjeff]

Carvers is on point as usual. Good stuff! While we take it with a grain of salt, you bet I'm wishing for that week 5-6 scenario when a broader area of below normal heights for the Continental US, and cutting off that awful blowtorch Chinook in Western Canada. Well, Calgary and Edmonton probably like it, lol...

If you believe the European monthlies verbatim (remember grain of salt) spring may start Martin Luther King Day. Weeklies stay seasonably cold through mid-January; but, the Euro month January is mild. Could that mean a warm last two weeks of January, or just a model choke? Amplified pattern right now could be giving it fits, but a warm regime later in January is a risk. February has been shown warm on both the CFS and Euro monthlies for a while.

I really do not favor a drastic regime change. Probably continue back and fourth. December should average cooler than normal despite the warm start. I have Jan/Feb slightly milder than normal, still colder than last year. No recent matches for slightly mild Jan. Feb 2016 and Feb 2011 are reasonable though.

[BullCityWx]

The 12Z NAM looked interesting for New Orleans/Mobile/Pensacola. 

[Carvers Gap]

13 minutes ago, Queencitywx said:

The 12Z NAM looked interesting for New Orleans/Mobile/Pensacola. 

We organizing a chase?

[Carvers Gap]

17 minutes ago, Queencitywx said:

The 12Z NAM looked interesting for New Orleans/Mobile/Pensacola. 

Seriously though, I debated on even mentioning the NAM.  Seems to always be too amped.  As a good wx hobby friend would say, the GFS has a progressive bias.  This is probably the Euro track.  Good luck for you all in NC.  We of course will be hoping for a westward jog...seems too late for a substantial one that we would need.

[John1122]

She's moved NW steadily. I could see some far eastern folks picking up flakes at the rate it's going. Longer range, still have to hope for clippers to bring the heat. Maybe get lucky and cook something up with the cold around. 

Curious as to whether the monthlies were showing a warm December a few months ago?

[BullCityWx]

2 hours ago, Carvers Gap said:

Seriously though, I debated on even mentioning the NAM.  Seems to always be too amped.  As a good wx hobby friend would say, the GFS has a progressive bias.  This is probably the Euro track.  Good luck for you all in NC.  We of course will be hoping for a westward jog...seems too late for a substantial one that we would need.

Honestly, I'd be surprised if the precip shield doesnt grow, given the jet pointed at us. 

[nrgjeff]

Euro Monthlies have been cold December and mild February since September. January has been zig zag city, not a huge surprise if it's the transition month.

1 hour ago, John1122 said:

...Curious as to whether the monthlies were showing a warm December a few months ago?

CFS changes by the hour, lol. Anyway I'm most interested in how January turns out. If it stays cold, 2010-2011 winter compares. If January turns mild we have not had a recent slightly mild January (+1 or +2). January has been cold or very mild.

Short-term: Friday flakes will likely be restricted to North Carolina mountains. Saturday might be only northeast of I-24 and at elevation. Blank CHA/BNA but TYS might get flurries and TRI could get a dusting. Maybe. Recommend observing from the Plateau or Mountains.

[Carvers Gap]

It will be interesting to see the spacing between events after this system passes to our SE.  The 18z GFS has a fantasy system at 210.   Interestingly, the Euro has the same system and similar synoptic set-up.  IMO, that may be a timeframe to watch.

[1234snow]

I would love to see some snowfall maps from the 18z NAVGEM. It was beautiful for the Valley and mountains. Of course it’s probably over amped but it may be sniffing something out at the 500 mb level. Has a cut off low over the Mid south and eventually has the clipper energy trying to phase in at the end.

I’m ready for another season of tracking these patterns and storms. I’ve looked at the models the past few weeks and have read your posts but never got around to posting. Some great discussion leading up to this winter.

[Carvers Gap]

With the 6z GEFS and 0z EPS depicting normal to AN temps during d10-15...I expect the Weeklies tonight to flip.  The operationals and their ensembles have been warming in the medium range for about three days.   The EPS was MAN this morning during that time frame.  I could be wrong, but the ridge building in from the West looks like it means business.  I still like the prospects of at least a potential storm before this happens during the d7-9 range.  It is possible that this is the move back to normal that the Weeklies depicted before another cold shot.  Going to be tough to move that ridge once in place.  The 0z EPS erases the NAO, but keeps the PNA.  It does try to retrograde the departing trough westward.  But that is a sprawling PNA.

[Carvers Gap]

I should clarify what I mean by flip.  I think the ridge out West holds....but forces the trough eastward to the point that we are normal to AN.  Almost like we will have to rely on backdoor cold fronts or storms to bring cold,. The cold will lurk just north of the border...but that ridge means business.  A neutral or +NAO is counterbalancing a strong PNA ridge.  Trough gets forced in to the NE.  Maybe that resets for another shot of cold...maybe it holds in place.  But I think the Weeklies will be different tonight in a significant way.  Hope I am wrong.

[Carvers Gap]

15 hours ago, 1234snow said:

I would love to see some snowfall maps from the 18z NAVGEM. It was beautiful for the Valley and mountains. Of course it’s probably over amped but it may be sniffing something out at the 500 mb level. Has a cut off low over the Mid south and eventually has the clipper energy trying to phase in at the end.

I’m ready for another season of tracking these patterns and storms. I’ve looked at the models the past few weeks and have read your posts but never got around to posting. Some great discussion leading up to this winter.

You need to post more!!!  

[Carvers Gap]

The end of the 12z GFS is where I hope this is where this is headed.  It reloads.

[Chattownsnow]

1 hour ago, Carvers Gap said:

The end of the 12z GFS is where I hope this is headed.  It reloads.

I like the timing and squashing of the s/w that the GFS shows around HR 210-240. My gut tells me that time period we score. I know a lot of others are talking about it also but it's just been muted because of the storm coming in a couple days. I believe a lot of folks are going to be disappointed with this weekend system. Hopefully the next storm we all score.  

[John1122]

The GFS is so dry we will have to look out for forest fires as we approach Christmas.

[Carvers Gap]

10 minutes ago, John1122 said:

The GFS is so dry we will have to look out for forest fires as we approach Christmas.

Do you think we stay that dry?  Definitely fits Niña climo. Monday's Weeklies were dry w AN snowfall.  I suspect tonight's run is not as cool.  Jeff had some good comments in the other December thread.  The 12z was cold for sure.  What winter are you comparing this to in your records?

[Carvers Gap]

32 minutes ago, Chattownsnow said:

I like the timing and squashing of the s/w that the GFS shows around HR 210-240. My gut tells me that time period we score. I know a lot of others are talking about it also but it's just been muted because of the storm coming in a couple days. I believe a lot of folks are going to be disappointed with this weekend system. Hopefully the next storm we all score.  

Those wave events are just tough to predict unless the cold has been there for some time.  I am loosely interested in whether we see some flakes on this side of the mountains, but not overly invested.  Even during our best winters, early December is not great climo and plenty of things are working against measurable snow...though it has happened in the past and will happen again.

[Wurbus]

It looks like the NAM and NAVGEM are trying to throw a little moisture into East TN with the upcoming system. Still doesn't look like a whole lot, but would be nice to see some light snow or flurries this early in December. Hopefully we can get something out of the potential system 8-10 days out.

[rdwhynot]

Woo Hoo  KBHM  (11:1 Ratio)

 

[Carvers Gap]

3 hours ago, rdwhynot said:

Woo Hoo  KBHM  (11:1 Ratio)

 

Good luck to you all.  Be sure to keep us updated!

[Carvers Gap]

Weeklies after week two are AN and sometimes seasonal.  Fits my thinking from this AM.  The PNA ridge out West spreads eastward.  It pushes the trough northeast.  It is an odd battle, but the SER is not the problem...it is the heat building out of the Southwest.  More later...

[Carvers Gap]

To add to the above...pattern gets a zonal look with the cold bottled up in Canada.  LR forecasting is a crapshoot.  If the Weeklies had been run from the 12z run of the Euro, it would have looked a bit different.  Overall, the trough will still be in the East but pulls back and even tries to retrograde a bit....but we loses the trough east of the Hawaii.  That is a nice signal for cold here. Will add more to this post later w the edit feature.  I will add that the snow mean is still good.  The control buries us.  Dry signal for the entire forum area....but still a similar snow mean to my Monday post.

[nrgjeff]

Yes I agree on the Euro weeklies. When I first saw AN heights over the SE 3/6 weeks I about threw my device through a window, but fortunately took a deep breath. No stubborn SER is forecast. Some warm days? Yes. However we'll have cold days too.

AN heights and surface temps come in here week 2 which is close to the 11-15 day period. Weeks 3-4 Southeast heights are at or slightly above normal but with zonal flow or even slightly cyclonic curvature. That's not a SER. 

After the week 2 warm-up, weeks 3-4 look variable averaging near normal. Weeks 3-4 are Christmas and New Years. Canada is a cold source region for the first time. Fast flow is likely through the Ohio Valley. We of course hope it will buckle favorably with cold air in place.

Weeks 5-6 are not bad either. Still some ridging sloshing around Texas with zonal or better flow this way. Will not worry about those weeks yet. Snow in South Texas today promotes optimism. 

[Carvers Gap]

Was definitely not a torch.  Normal to slightly above normal will get the job done in January.  I agree w Jeff...the Weeklies definitely have some windows for storms.  The snow mean was decent despite a dry pattern.  When the pattern is bad...normally the snow mean is not good.  It was still decent.

[Carvers Gap]

Snow means from the Weeklies...

Bristol/Elizabethton/SW VA: 12-13”

Knoxville: 6”

Nashville: 4”

Bolivar: 3”

Memphis: 2+”

North Alabama and MS were similar to last time w 2” and slightly more where the current weekend storm is forecast.  

[JayCee]

Light, steady snow falling this morning on the drive to work east of Sevierville in the foothills.  Looks like we could possibly see up to an inch here today.  Just east of here, the mountains and the Asheville area could get 5 or more inches of snow.