Tennessee Valley 2019 Fall Speculation/Forecasting

[Carvers Gap]

Some definite trends(all though not super consistent at this point...about 2/3 of the time) in placing the trough out West on most global modeling ensembles at 0z. Those trends on modeling began last week.  I don't think they are set in stone yet, but frequency of AN heights(in the East) on modeling in the LR is increasing.  On the 0z GEFS the Aleutian low begins to disappear though the block over Greenland is there.  I do hold out hope for a full latitude trough over NA.  But honestly, looks like models are trying to decide if the trough stays in the West...or rolls eastward.  Seems like the lean is West.  Tough to find many Decembers that are cool with this SST set-up.  So, if it does get cold in December and stay cold...pulling a bit of a needle out of a haystack.  

[Carvers Gap]

The 0z Euro continues to show fairly strong warming at 10mb at high latitudes.   Have to think that is playing some part in the flip-flopping of modeling.  It has in the past.  Also means the PV is really gonna get bumped around.

[Carvers Gap]

12z GEFS continues to portray the western trough establishing itself early next week.  Not sure I buy that yet....but it is growing more consistent with this feature.  Pretty steady evolution of a flip of its original output over the past 5-6 model runs.  IMHO, I think the current cold pattern has just about run its course.  Only way we can dodge a big warm-up is if the NAO can go negative and mute what is an MJO that is trending into a tour of the warm phases(maybe at a decent amplitude at that).  The other wild card is the SSW.  This very well maybe a run-up pattern to that as described in my post yesterday.  If that occurs, later December/early January would likely have some strong cold anomalies somewhere over NA...good luck guessing where!  Not great signs for December at this point, especially with the GEFS moving the pattern flip to within seven days.  

[Carvers Gap]

Preliminary thoughts on December.  AN(maybe one torch week in weeks 2-3) weeks 1-3...transition of seasonal or cold by week 4.  SSW and -NAO(how long does it last) are big wild cards.   

[Carvers Gap]

Was a ton of discussion about this yesterday.  The 12z GFS today shows significant warming at high latitudes and in the stratosphere of that area.  Not saying an SSW is imminent, but the foundation is being laid at least for a pretty significant disruption.  Waaay out there, but look what the 12z GFS is doing.  These are the 10mb temp anomalies.  I normally would never post at this range, but the GFS/GEFS combo nailed the strat split(from 16 days out!) during the spring of 2018 and did pretty well last winter with this type of event.  The Euro is showing signs warming late in its run.  Also Typhoon Tip in the NE forum commented that this is a pretty sudden change in modeling and needs to be paid attention to...I concur.  

 

Here is a screenshot....fairly exciting stuff.

[Carvers Gap]

I'll say it.  This pattern looks remarkably similar to 1954...and last year.  November cold...talk of an SSW...warm December now in the works.  The only difference right now is the Euro Weeklies are not showing a cold winter - pretty much a torch after week 3, but when have they not?  Weeklies do not show a cold pattern and pretty much dump the cold in the northern Rockies.  Looks like(once we reach late November) that the pattern will indeed revert to the base pattern from the last twelve months for at least a little while and maybe longer.  The storm track and cold air placement are remarkably similar as well.  I say bring on the SSW...We are going to need something to shake-up the pattern.  Lastly, with the potential for an SSW...pretty much all bets are off.  That is especially good if one believes the Euro Weeklies which I am not sure that I do.  Glad we got some early season snow and cold...going to be a while before we see much more IMHO.  Thinking late December or even January before we get into a better cycle.  Pretty stark change in modeling over the past 48 hours.  Again, the one possible good thing is the strat warming event.  That is going to wreck any LR model run until it gets that right.  

[BuffaloWeather]

1 hour ago, Carvers Gap said:

I'll say it.  This pattern looks remarkably similar to 1954...and last year.  November cold...talk of an SSW...warm December now in the works.  The only difference right now is the Euro Weeklies are not showing a cold winter - pretty much a torch after week 3, but when have they not?  Weeklies do not show a cold pattern and pretty much dump the cold in the northern Rockies.  Looks like(once we reach late November) that the pattern will indeed revert to the base pattern from the last twelve months for at least a little while and maybe longer.  The storm track and cold air placement are remarkably similar as well.  I say bring on the SSW...We are going to need something to shake-up the pattern.  Lastly, with the potential for an SSW...pretty much all bets are off.  That is especially good if one believes the Euro Weeklies which I am not sure that I do.  Glad we got some early season snow and cold...going to be a while before we see much more IMHO.  Thinking late December or even January before we get into a better cycle.  Pretty stark change in modeling over the past 48 hours.  Again, the one possible good thing is the strat warming event.  That is going to wreck any LR model run until it gets that right.  

The euro weeklies beyond week 3 are nearly completely unreliable. 

[Holston_River_Rambler]

I think the tropical mess is definitely different this year. I just hope it leads to a good snowsome outcome.

Last year's tropical convection was stuck in the Indonesia area was driving the SSW and I think there was even some discussion of it creating a feedback loop. Looks like it is the same situation this year, but in a very different region, over the western Indian Ocean and Africa. 

EPS thinks it wants to stay there for a bit. 

What's extra interesting to me right now is having the best tropical forcing further west is being projected to have a similar result. Last year the catch phrase was mountain torque and Masiello seemed to suggest at least once that MSLPs in East Asia were facilitating a more efficient transport of heat to the strat at high latitudes. Of course that's only if I even came close to interpreting him correctly. It kinda made sense at least in a visual way. Tropical forcing shaped the expanded Hadley cells in  and they and Ferrell cells helped guide the jet(s). SSW helped lower the tropopause in the tropics and cold airmasses in Siberia dropping down even made it to the Phillippines and all this helped maintain convection where it was. 

My question is now how is all this going to play out with a new year and obviously new circumstances. We're definitely not doing loop de loops in MJO phases 4-5-6 this year! 

Does the forcing further west lead to more Ural mountain torque instead of Himalayan? TBH I'm not even sure what that means, but surely it can't have entirely the same result or can it?  

Very interesting too to see some of the divergent thoughts folks have on how the winter will play out in the broader AmWx forums and wxtwitter. Isotherm emphatically says toasty east of the Rockies D - J, but seems a bit more cautious for Feb - March, based on the descending QBO and possible high-latitude blocking developing then. Isotherm was also firmly against there being anything like a  SSW before mid to late Jan.  Griteater seems fairly optimistic to me and emphasizes the IOD and a -NAO. Isotherm only mentions it the IOD once and argues for a predominantly +NAO.  On the other hand, Grit thinks that the "The NPac SST pattern [will] evolve thru winter based on the winter 500mb pattern.  For example, a pattern with an anchored Aleutian Low and Western North America ridging would lead to a +PDO SST structure." Isotherm went negative on the PDO.  Raindancewx is like Grit, but to paraphrase him, a tad further west with the cold anomalies. Eric Webb seems to be all about a warm December (#loltorch?) and Masiello wants to stay by his fire from late Dec on. Does he just like fires? Or is he showing his hand? After trying to decipher him last winter, I'm not so sure. 

Gun to my head, I'm watching the tropics to see where the convection sets up and how that effects the jet.

But this winter just feels different and colder to me so far. Will be interesting to follow the strat. for a bit and how models deal with the MJO being in the COD. 

 

 

 

[Carvers Gap]

19 minutes ago, BuffaloWeather said:

The euro weeklies beyond week 3 are nearly completely unreliable. 

Don’t disagree.  Like I said, if this SSW is legit...nothing is realiable until it works itself out.  Now, Weeklies can give us hints...but it’s warm bias makes it unreliable right now.  In this case, absent and SSW, it does make sense to have a warm December given climatology.  However, if we have a cold December...you can thank me for the reverse mojo.  LOL.

[Carvers Gap]

I don’t think things are exactly like last year, but there are some strong similarities.  Things that aren’t the same are the QBO trajectory, the SOI is in sync now(remember last year it was a Niña phase during a Nino), and it’s not last year.  But there are definite similarities.  In truth, just no idea where this goes after the SSW.  I could make a pretty good case that the strat warm likely caused the eastern winter to be warm last year when the cold dumped west.  Does lightning strike twice in the same cold spot?  Probably not.  My hope is that we pull an 09-10 rabbit out of the hat.

[Carvers Gap]

Lastly,  the potential SSW is going to be fun to follow while we hit this pattern that doesn’t support snow.  Usually we don’t have anything follow at this time of year.

[Carvers Gap]

Some nice trends on modeling overnight...Both the 0z EPS and 12z GEFS seemed to take steps in the right direction, mainly both found the -NAO that had been a prominent feature until the past few runs.  Let's see if they hold at 12z.  Again, have to think this SSW(minor or major...no idea) is causing issues understandably.  

[Carvers Gap]

@nrgjeff, time to jump into the fray.  What ya got?

[Daniel Boone]

This period coming up is going to be tough. So many variables juggling for position. 

[Carvers Gap]

7 hours ago, Daniel Boone said:

This period coming up is going to be tough. So many variables juggling for position. 

DB...you had some good thoughts in the main ENSO thread.   I have considered the full latitude trough option for the U.S.....It was good to hear someone else say it.  The ridge in the eastern Pac and the -NAO would argue for that pattern I think.  Again, really good thoughts.

[Daniel Boone]

Thanks buddy.  Just being an old timer with experience and memories that help. 

   Brother, you definitely add valuable insight to the forums. 

Let's hope the Ghost of those winters of yore pay a visit . Although, I couldn't enjoy them like I used to. Tough to handle the cold anymore.

[Holston_River_Rambler]

Pretty trend of the trend on the GEFS over the pst few runs: 

EPS not bad either:

 

 

 

 

[TellicoWx]

Great discussion everyone, I also find the part about a possible SSW event intriguing cause it lines up with the two years I'm looking into...2002 and 2004. I like using the top down method for the atmosphere and looking longer range. Since 1948, only 02 and 04 are close to where the QBO is currently at as far as reading plus trend. Both years also were close to a neutral state ONI, granted this year we are closer to actual 0 than those 2 (.6 and .9). Both 02 and 04 featured a wintertime SSW event as well. But that is where the similarities end for 02 and 04. While both started close to avg for the month of Dec temp wise, Jan and Feb went in complete opposites. 2002 went cold for both, while 2004 torched to a degree. The AO/NAO combo was complete opposites as well. The divergence in those two setups, is the SST near Alaska, warm pool there assisted the ridging along the west coast in being a predominant feature. While 04 was a cold pool state allowing the cold to stay bottled over Canada and warm Pacific air to flood the continental US. We are in a warm SST currently (ridge promotions), QBO has been falling (trend is more important than reading) which acts as a primer for dislodging the PV. If the NAO can sync up with the ridging, we could definitely see the cold drop coast to coast at some point. Those SST off Alaska is a big key for us and I don't think LR modeling has that completely worked out. So with the current setup, I think Dec will end up close to avg, with a BN Jan, and slightly BN Feb (based on fairly good odds of a weak/mod SSW event coupled with the SST). If we lose the warm pool and the EPO doesn't go moderately negative, the keep the shorts handy lol.

Sent from my SM-S767VL using Tapatalk

[Carvers Gap]

12z GFS as well as 6z GFS are advertising an Arctic origin air mass late in both runs.  12z is still running.  That is frigid.  Some -30+ stuff streaming across the pole from Siberia.

[Carvers Gap]

And there is Boone's full latitude trough...right on time.  

[Carvers Gap]

Kind of a fun weather day on ensembles.  Lots of positives to talk about(like that?).   We will see if the trend continues tomorrow.  As someone said in the MA forum, I am a tad bit wary after seeing such great modeling last year...only to have the rug pulled out at the last minute.  Very strong block being portrayed for early December.  Here's to 0z not flip-flopping back to a less favorable pattern.  Today's looks were pretty awesome.  

[Mr. Kevin]

49 minutes ago, Carvers Gap said:

Kind of a fun weather day on ensembles.  Lots of positives to talk about(like that?).   We will see if the trend continues tomorrow.  As someone said in the MA forum, I am a tad bit wary after seeing such great modeling last year...only to have the rug pulled out at the last minute.  Very strong block being portrayed for early December.  Here's to 0z not flip-flopping back to a less favorable pattern.  Today's looks were pretty awesome.  

Carver, im intrigued about the possible SSW event. Last year it didnt propagate correctly. They are tricky. Would the teleconnections do dramatic things if the SSW is the real deal? I was curious about that. 

[TellicoWx]

2 hours ago, Carvers Gap said:

Kind of a fun weather day on ensembles.  Lots of positives to talk about(like that?).   We will see if the trend continues tomorrow.  As someone said in the MA forum, I am a tad bit wary after seeing such great modeling last year...only to have the rug pulled out at the last minute.  Very strong block being portrayed for early December.  Here's to 0z not flip-flopping back to a less favorable pattern.  Today's looks were pretty awesome.  

If the GEFS is anywhere in the right ballpark on the EPO, a big time shot of cold is about to drop into the central/eastern US. The Pacific is our biggest driver and can overcome a not favorable AO/NAO. -AO/-NAO can help lock the EPO in for longer periods of time. Last year with the strengthening going on with the PV (QBO rising), it would have taken a serious -EPO/-NAO regime to dislodge a decent lobe south. With the opposite happening so far entering winter (QBO in decline), I don't think the modeling will be anywhere as bad. Just don't need the QBO to stall or start rising.

[Carvers Gap]

Pretty amazing to see the LR models flip-flop all over the place right now.  It is not unusual for sure, but pretty much every day now in the d9-15 range - massive changes in the NA circulation pattern.  The EPO ridge is so tall on the 6z GEFS that it tucks a trough underneath it.  Saw that most of last winter.  So, we definitely want an EPO ridge..but not on steroids where the trough can tuck under it.  The -NAO helps on the GEFS.  On the EPS, the ridge is far enough West that the cold dumps West.  It has a weaker -NAO.  I am just wary right now.  Last year, many models were almost universally cold in their depiction through mid-December.  After that early snowstorm in NE TN, the models flipped to a big EPO ridge with a trough tucked under it.  In the middle of all of that was a big SSW event.  I think until that event happens, modeling cannot be trusted during and beyond that event(minor or major).  Also, can't tel much until that -NAO establishes.  Once in place, very stubborn to move and models will almost always break it down too quickly.  

[Carvers Gap]

Working through modeling, Twitter, JMA, and even a little JB this AM....I think the cold start to December is plausible.  I have seen some 1960s analogs being tossed around.  I do agree that the setup being portrayed is a bit unusual in that teleconnections favor both an eastern and western trough.  Pac is favorable for the West.  Atlantic is favorable for the East.  There are significant differences in how the American model and Euro model are handling the MJO.  The GEFS is taking the MJO through the COD and back into the cold phases.  The ECMWF crawls(and I mean crawls) through the warm phases of the MJO.  That might be why we are seeing some differences in modeling.  The GEFS has handled things better in the d10-15 range lately.  I never completely trust any model, but especially not the GFS/GEFS combo.  That said, they have don really well.   Here is the MJO link so you can see for yourself...

https://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/clivar_wh.shtml

[Carvers Gap]

That -68F over Greenland at 324?  Has the GFS ever gone that low on this side of the globe?  Not sure I remember seeing anything remotely that cold on the GFS in that area.

[Carvers Gap]

13 hours ago, Mr. Kevin said:

Carver, im intrigued about the possible SSW event. Last year it didnt propagate correctly. They are tricky. Would the teleconnections do dramatic things if the SSW is the real deal? I was curious about that. 

SSWs in my opinion are like letting a bull loose in a china shop....The only thing predictable is that it is going to wreck havoc.  Seemed like last January's SSW did actually propagate downward fairly effectively into two or three daughter vortices at the tropospheric level.  There was extreme cold associated with and record snowfall in western Montana and western Wyoming.  One might make an argument that it took nearly ten months for those effects to wear off.  They had snow well into May and June at 6,000' out there.  Their warm season lasted only from July to August, before winter came very early.  Unpredictably severe cold is often associated with them.  Plenty of SSWs do "fail."  I think we just want it properly shaken...not stirred.  Sorry...couldn't resist.

[Carvers Gap]

Look at the min for the region shown on this map from the 12z GFS.  -77.1F!!!  Looks like our source region for cold is getting a bit better.

[tnweathernut]

Good discussions here the last few days.  Thanks for the maps, Carvers!  

This is probably the calm before the storm.  It has been a LONG time since we have seen early season blocking in Greenland come to fruition.  We have seen it as a mirage virtually every winter this decade at long leads, but it almost never materializes.  If blocking forms as universally projected as a closed circulation (now well within day 4) our chances of scoring a system to track go way up IMO. 

This kind of a block won't typically break down easily and can last for longer than modeling tends to indicate.  It may take some time to attain a workable Pacific and/or work cold enough air into the pattern, but should the Pacific not align in a fashion that sends a deep trough into the west,  it's not unreasonable we would have something to track around the first part of December.  

If what happens in November the winter will remember, we may be in for a memorable year in the snow/ice department.

[Daniel Boone]

I see CPC IS going warm for most of the country for December. Following those climate models. Of course, cpc is warn biased anyway as most of us know.