December 2020 Medium/Long Term Pattern Discussion.

[Holston_River_Rambler]

6z Euro doesn't quite out as far as we would like, but it does look east of 0z run:

6z:

 

0z:

 

Southern stream energy was more open and the N stream can bully it more easterly 

[Carvers Gap]

SLP on the off-run(which only goes out so far as Holston noted above) is weaker and slower.   It is about 3 mb weaker.  Looks like that would run slightly south and east of the 0z run if it could go that far.  Likely means the Euro corrected a bit by not overamping the slp too early.  The precip shield in Illinois has sagged south.  Definitely less energy heading into west TN than compared to 0z.  

[Carvers Gap]

11 minutes ago, Holston_River_Rambler said:

6z Euro doesn't quite out as far as we would like, but it does look east of 0z run:

6z:

 

0z:

 

Southern stream energy was more open and the N stream cam bully it more easterly 

Great comparison graphic.  Because it is slower, I can't be sure that it will not gain a bunch of latitude, but yeah, definitely can see that less energy is making it into west TN.  I think the phases on this is crucial.  Seems like each run of each model is slightly different.  This is one of those systems that has a chance to go east of the Apps at the last minute...but tough to know.  Would not be surprised to see the SE jog continue a bit today...only to see a NW jog at the last minute.  I suspect the block over the top is being felt a bit more.  But really, that is some educated guesswork on my part.  But hey, at least we are tracking a storm on Thanksgiving!

[Carvers Gap]

Kind of a weird deal...but this is becoming a finesse solution for snow.  The stronger it is, the more it cuts west of the Apps but also pulls in cold air and has wrap around.  The weaker it is, the more it pulls east of the Apps but is more of a rainer.  Still not convinced this doesn't run through NC as a pretty strong storm.  When the solutions run up the spine of the Apps, the storm weakens.  The SLP needs to be either west or east of the Apps in order to get a strong solution.  

[Holston_River_Rambler]

6z EPS MSLPs are a little(and I mean a tad)  further south, but still a pretty tight wad of 'em around TN:

6z:

 

 

0z

 

 

[Carvers Gap]

Splitting hairs at this point, but I am noticing a cluster of lows build south and west of 0z in Georgia and Alabama (area within the blue circle).  There are fewer far to the west around the TN northern border and into western Ohio and eastern Indiana.  Tells me the Euro is consolidating on a track that is a bit more east.  How far?  No idea.  "Might" mean the model has more room to slow down and trend SE.  That slower bundle would allow for the storm to turn north much further eastward.  6z is on the left and 0z on the right.   Something to keep an eye on....

 

[Carvers Gap]

The 12z NAM has the storm now.  Not nearly as wrapped-up as one would expect from a model which has a bias of over amplifying systems. All usual caveats for the NAM at range do apply.

[Holston_River_Rambler]

Euro has come east some at 12z, but not enough. Surface low runs right up I 75 in the eastern valley. 

[Daniel Boone]

Here ya go guys. That one ruled the roost here as far as November Snowstorms.  A true Blizzard ! Cars were completely covered here in Lee County from huge drifts . Higher eles. of County received 2 ft.+. Drifts much higher. Temps were in teens during day. 

[Snownado]

11 minutes ago, Daniel Boone said:

Here ya go guys. That one ruled the roost here as far as November Snowstorms.  A true Blizzard ! Cars were completely covered here in Lee County from huge drifts . Higher eles. of County received 2 ft.+. Drifts much higher. Temps were in teens during day. 

How does Berea get 10, Richmond get 6, and Lexington get 10 ?

[Holston_River_Rambler]

This is a little bit bantery, but it is a holiday, so why not? Aren't we in that weird window we sometimes notice between days 3 - 5 when models lose storms or flip-flop, only for them to pop back up. 

[ShawnEastTN]

This is a little bit bantery, but it is a holiday, so why not? Aren't we in that weird window we sometimes notice between days 3 - 5 when models lose storms or flip-flop, only for them to pop back up. 

Absolutely! At least it used to always be that way right about this timeframe we lose it and hope is dashed then triumphantly comes back about 24 hours later. Hopefully the case here but it is 2020 so probably going to evolve to massive severe event and no freezing precip except damaging hail.

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[John1122]

54 minutes ago, Daniel Boone said:

Here ya go guys. That one ruled the roost here as far as November Snowstorms.  A true Blizzard ! Cars were completely covered here in Lee County from huge drifts . Higher eles. of County received 2 ft.+. Drifts much higher. Temps were in teens during day. 

That snow map has always been off. My dad always said that the snow was over the bumpers of cars during that event. So I think it underestimates totals almost across the board. 

[John1122]

35 minutes ago, Holston_River_Rambler said:

This is a little bit bantery, but it is a holiday, so why not? Aren't we in that weird window we sometimes notice between days 3 - 5 when models lose storms or flip-flop, only for them to pop back up. 

After the last three years it's basically don't trust a model if it is showing accumulating snow at any point. You'd be right 95 percent of the time doing just that. 

[Holston_River_Rambler]

FWIW the 12z Ukie is even further east now, from being the furthest west:

 

 

 

[Olhausen]

1 hour ago, Blue Moon said:

The globals have pulled accumulating snow out of Middle Tennessee almost entirely. Quite the change the last 24 hours.

Man, it seems the last few years this has happened a lot. Models showing a good snow run after run 7-5 days out and then 3-4 days out it loses it all. I’m usually good at not even worrying about getting snow till January since it’s so often the case in middle Tennessee. This one though I was letting myself get excited due to the fact it’s been 10 years since my area got a real snow in December and the law of averages says Were due. Hopefully a miracle will happen and things will trend back in our favor even though the chance is slim.

[Carvers Gap]

Trends I noticed...Euro operational looks the same.  GFS and GEM are still east of the Apps and not moving much either (though their ensembles moved west...but still east of the Apps).  I think the storm is getting shredded by the solutions which go directly up the Apps - similar to a hurricane hitting Cuba or the DR.  The phase on this is really tricky.  I think a phased system is likely.  Do I think modeling has that phase molded correctly yet?  Nope, but they are getting a bit better.  It does look like accumulations are moving north and east with each run.  If you are E TN, you want to see the storm go east of the Apps and then spin up(seems like this storm may not enough separation between us and the storm track at this juncture).  If you live in middle or west TN, the entire consolidated storm needs to be strong and west of the Apps.  Right now, the storm is splitting the difference between the two and getting washed out.  As for overall trends, I tend to lean towards a track which sends some energy up west of the Apps but the primary going just east over Asheville.  That is not wish casting by me, because that doesn't get the job done IMBY.  We will see what happens...I just don't think the models have the phase down quite yet.

[Carvers Gap]

In a lot of ways, these remind me of the slp bowling balls which we see during spring.  Those tend to hold surprises and wonder around like a drunken sailor - terribly tough to predict.  Just look at the second storm on the Euro as an example.

[Carvers Gap]

Great write-up by MRX.  Really applies to the entire forum area in many ways...

https://forecast.weather.gov/product.php?site=MRX&issuedby=MRX&product=AFD&format=CI&version=1&glossary=1

[Holston_River_Rambler]

Sunrise over our little N stream friend in the Gulf of Alaska:

 

[Daniel Boone]

2 hours ago, John1122 said:

That snow map has always been off. My dad always said that the snow was over the bumpers of cars during that event. So I think it underestimates totals almost across the board. 

Agree John. Also, measurements were taken different back then by some. They would measure after snow ended and settled. Also, during drifting events they would measure the leveled or lowest area instead of different locations for an average.

[John1122]

18z suite generally agrees with earlier runs. Looking more like elevated areas are probably going to be it for accumulation but there may be flakes in the air for a much wider area.  The models haven't resolved their issues outside of 36-48 hours that were prevalent the last two years. Especially the ensemble means. 

Backside events rarely work very well. Models almost always over do moisture associated with them. Looks like that's going to end up being the case again with this event.  If I can go out and see snow falling, that's a win these days. 

[John1122]

The Canadian is the most consistent model. The GFS moved the track 400ish miles in the past 24 hours. The NAM is further east than either model but it's the late run NAM. 

If I were making a guess none are right right now but the track will probably be somewhere in their window. 

The GFS was the least snowy model,  the NAM looked like it was going to be healthy for the Northern midstate. The Canadian is friendly to that area too. 

[Holston_River_Rambler]

Looking more and more like it will make a run up just west of or over the Apps. Still time for some surprises though. 

On the bright side, the EPS members see hope for at least a solid dusting for the usual upslope areas and even a chance for valley areas:

 

 

 

 

 

 

 

 

[Holston_River_Rambler]

I will say the 6z RGEM has an interesting solution at the end of its run. The initial low does run up west of the Apps, but N Stream energy drops in and cuts off and provides some lift:

[Carvers Gap]

Long Range Update(at least from my perspective, and as Jeff would say, certainly open for debate!)....

In the LR, this morning's 0z EPS has moved a trough into EPO/PNA region after d12.  Trough is still in the East as well, but looks like a retrograde to a ridge is underway.  Interesting feature is a -NAO in conjunction with the western trough.  That would actually work, and would create nation wide cold driven by cold invasion the West and spreading eastward.  The problem is that -NAOs on modeling have rarely verified, and even if they do, just for a fraction of the time and strength originally modeled during recent winters.  

Euro Weeklies update (from last evening) has a similar solution though this morning's 0z run is certainly more aggressive and quicker in establishing the western trough.  Interesting thing to watch will be the weak AN heights over the Davis Straits which are persistent after Dec 20 and after the -NAO from Dec 10-20.  Looks like there will be temporary intrusions of cold after the 20th with the base pattern for winter beginning to take hold which is a trough in the Northwest.  Will it happen?  Not sure.  The Euro Weeklies sure missed(like totally whiffed) on this upcoming trough amplification as recently as two weeks ago.  Also of note, the last 4 runs have certainly evolved into a "less hostile" look over the East after Dec 20th..  Could it be that we finally get a -NAO during winter which will mute the upcoming warm phases of the MJO?  Don't bet on it...but given how winter has started with a big surprise, I wouldn't bet against it either.  On the subject of the Euro, today's run of the MJO on the NCEP site loops the MJO in the null phase and certainly looks poised to head into the warm phase tour.

I would say right now that given the complete whiff by the Weeklies on the early December pattern, take it with a bit of a grain of salt.  Also important to remember that the Weeklies do have a tendency to settle down and become a bit more accurate(as accurate as a 4-7 week model can be) as the winter season settles in.  Of note the GEFS Extended Ensemble locks in an eastern ridge beginning around Dec. 19th and never looks back through the end of its run which is Dec 31.  So, the Weeklies do have some support though LR modeling (of the variety past 3 weeks) do have a warm bias at times.

Of note the 6z GEFS nor the 0z GEPS most recent runs do not have the 0z EPS look.  Both still have an eastern trough.  Have to think the GEFS will flip soon as its MJO from yesterday took the warm tour.  An important note is that the MJO is a bit weaker than last year west of the dateline.   I definitely give some increased cred to the Canadian ensemble as it has just schooled the GEFS and EPS on the upcoming pattern.  No idea what the global verification scores will look like, but it appears to have nailed the short term upcoming pattern over the SE prior to other models.  The  GEPS has been decent of late and will hold more weight than normal for now in my book.   

Lastly, when I see a big mid-Atlantic ridge which sort of retrogrades into a WAR(western Atlantic ridge), makes me think that the SPV(polar vortex at 10mb) is going to get hammered.  There is plenty of chatter about a SSW on Twitter for sure, and has been for a few days.  However, the aforementioned ridges are also a great hint other than the Twittersphere.  That might be why a -NAO is beginning to show up as the SPV is getting jostled around.  I do think we need to be wary as the last two winters have featured lots of failed or less than advantageous PV splits and false -NAOs(after much wx model advertising).  However, the start to winter for early Dec appears to feature an abrupt change in modeling (to cold) and would not surprise me to see that happen 1-2 more times for 10 day time frames.  

Also, important to remember that early winter is a very tough time to score IMBY.  As some have noted though, that has been the trend of late - early season snows in various micro-climates (meaning not widespread) followed by meh winters.  Still, the problem is that often cold is still marginal at this latitude in early December.  Hopefully, we can get some snow showers in E TN with the first system this week and maybe middle and/or west TN can grab some low elevation snow as well.  The 6z off run of the Euro certainly implied that.  Next system is all over the place on modeling...so will have to watch that one closely.

[Carvers Gap]

If there is one potential bias I am noticing(it seems across the board on all operational modeling), is the tendency to over amplify in the d5-7 time frame - even stalling systems for long periods of time.  

[Daniel Boone]

2 hours ago, Carvers Gap said:

Long Range Update(at least from my perspective, and as Jeff would say, certainly open for debate!)....

In the LR, this morning's 0z EPS has moved a trough into EPO/PNA region after d12.  Trough is still in the East as well, but looks like a retrograde to a ridge is underway.  Interesting feature is a -NAO in conjunction with the western trough.  That would actually work, and would create nation wide cold driven by cold invasion the West and spreading eastward.  The problem is that -NAOs on modeling have rarely verified, and even if they do, just for a fraction of the time and strength originally modeled during recent winters.  

Euro Weeklies update (from last evening) has a similar solution though this morning's 0z run is certainly more aggressive and quicker in establishing the western trough.  Interesting thing to watch will be the weak AN heights over the Davis Straits which are persistent after Dec 20 and after the -NAO from Dec 10-20.  Looks like there will be temporary intrusions of cold after the 20th with the base pattern for winter beginning to take hold which is a trough in the Northwest.  Will it happen?  Not sure.  The Euro Weeklies sure missed(like totally whiffed) on this upcoming trough amplification as recently as two weeks ago.  Also of note, the last 4 runs have certainly evolved into a "less hostile" look over the East after Dec 20th..  Could it be that we finally get a -NAO during winter which will mute the upcoming warm phases of the MJO?  Don't bet on it...but given how winter has started with a big surprise, I wouldn't bet against it either.  On the subject of the Euro, today's run of the MJO on the NCEP site loops the MJO in the null phase and certainly looks poised to head into the warm phase tour.

I would say right now that given the complete whiff by the Weeklies on the early December pattern, take it with a bit of a grain of salt.  Also important to remember that the Weeklies do have a tendency to settle down and become a bit more accurate(as accurate as a 4-7 week model can be) as the winter season settles in.  Of note the GEFS Extended Ensemble locks in an eastern ridge beginning around Dec. 19th and never looks back through the end of its run which is Dec 31.  So, the Weeklies do have some support though LR modeling (of the variety past 3 weeks) do have a warm bias at times.

Of note the 6z GEFS nor the 0z GEPS most recent runs do not have the 0z EPS look.  Both still have an eastern trough.  Have to think the GEFS will flip soon as its MJO from yesterday took the warm tour.  An important note is that the MJO is a bit weaker than last year west of the dateline.   I definitely give some increased cred to the Canadian ensemble as it has just schooled the GEFS and EPS on the upcoming pattern.  No idea what the global verification scores will look like, but it appears to have nailed the short term upcoming pattern over the SE prior to other models.  The  GEPS has been decent of late and will hold more weight than normal for now in my book.   

Lastly, when I see a big mid-Atlantic ridge which sort of retrogrades into a WAR(western Atlantic ridge), makes me think that the SPV(polar vortex at 10mb) is going to get hammered.  There is plenty of chatter about a SSW on Twitter for sure, and has been for a few days.  However, the aforementioned ridges are also a great hint other than the Twittersphere.  That might be why a -NAO is beginning to show up as the SPV is getting jostled around.  I do think we need to be wary as the last two winters have featured lots of failed or less than advantageous PV splits and false -NAOs(after much wx model advertising).  However, the start to winter for early Dec appears to feature an abrupt change in modeling (to cold) and would not surprise me to see that happen 1-2 more times for 10 day time frames.  

Also, important to remember that early winter is a very tough time to score IMBY.  As some have noted though, that has been the trend of late - early season snows in various micro-climates (meaning not widespread) followed by meh winters.  Still, the problem is that often cold is still marginal at this latitude in early December.  Hopefully, we can get some snow showers in E TN with the first system this week and maybe middle and/or west TN can grab some low elevation snow as well.  The 6z off run of the Euro certainly implied that.  Next system is all over the place on modeling...so will have to watch that one closely.

One thing of note, especially with LR modeling is the heavy weighting of ENSO. So, this could be alot of the shifting to the western trough. Of course, may very well happen and of course with the strength of La niña,  odds favor that.

[Carvers Gap]

Was interesting to see the 12z GFS shift to a Miller A for the second system.  

[Carvers Gap]

Second storm on the 12z Euro is not going be that westerly cutter.