December 2025 Short/Medium Range Forecast Thread

[John1122]

Ironically, the GFS ensembles agree more closely at 500 than the Euro in general, and not with it's OP which is a massive WC trough/EC ridge.

 

[Daniel Boone]

The MJO appears to be progressing ideally for our Area through December. However, the AO and NAO are not if guidance were to be right. Of course, those Domains cannot be forecasted with great accuracy, particularly the NAO. 

      The good thing that can mitigate the Effects of the positve Arctic Oscillation Modes is the weak south displaced PV. We saw that in 2015 and a couple recent Years. However, if you want much greater Odds for across the Board Snowstorms you want the Arctic Domain Negative. As witnessed , most notably in 2015, Northern Area's can do well as long as the PV is weak and displaced well South in Canada.

[jaxjagman]

11 hours ago, jaxjagman said:

Check it out this winter if the MJO gets back to P5,ill look for an archive but i doubt its the same

The MJO was fairly chaotic into Maritime/WP this cycle but it was into still the Maritome the first week of Nov,i need to go back and read it more thoroughly for myself,thanks for sharing this,John

[Carvers Gap]

Pretty chilly 12z suite incoming so far.  Triptofan shut me down last night…so I missed the torch!  LOL

[John1122]

GFS torched because it killed the MJO and headed it back kinda towards 6 in the COD.

[GBOVolz]

Pretty chilly 12z suite incoming so far.  Triptofan shut me down last night…so I missed the torch!  LOL

PowellVols is in. Had to start a new account, new email


.

[Carvers Gap]

59 minutes ago, GBOVolz said:

PowellVols is in. Had to start a new account, new email


.

Glad to have you back, man!!!

[Carvers Gap]

Pretty good 12z run from the 12z GDPS para and 12z Euro(Dr No?!)....

 

[Matthew70]

Let the snow fall as much as it would like in December!  

[Carvers Gap]

I should add that climatology kind of doesn't like snow during early December in the valleys.  But during the last 15 years, it has allowed for it.  Anyway, this was the GMON from yesterday.  22 days in phase 8!

[Carvers Gap]

@John1122 is definitely on the money with the 0z GFS not even getting to phase 8.  I "think" that GFS plot is hopefully an outlier.   But....definitely something to keep an eye on, and as always, a very keen observation from John to spot that.  I "think" the 12z GFS began to correct that.

I would take the GMON above and shift that stall to the phase 7/8 border.  If it was January, I would be far more concerned w/ the faster rotation into 6.  But really, I am always concerned it rotates back into 6 - even if it wasn't showing it!  

I wonder when/if the SSW begins to show at the end of deterministic runs.  By the end of next week, we may start to see that influence at the end of those deterministic runs.

[Carvers Gap]

One more thing in a flurry of posts, I am beginning to see evidence that the NAO may begin to fire.  It is notoriously hard to predict, but it is significant in both the CMC and Euro 12z runs.  It is very evident on the 12z EPS and to some extent the 12z GEPS.  That is a BIG difference between the CMC/Euro vs GFS.  

[Carvers Gap]

I am waiting on the 12z EPS to fully populate so I can grab 5 and 10 day maps of 500 anomalies.  But here is the deterministic d10-15.   NAO and EPO regions both look good.

[Carvers Gap]

I deleted the four map comparison of temps above.  WxBell hasn't loaded the 12z d10-15 temp maps for the EPS.  It had defaulted to 0z, and I didn't catch it until now.  I should be colder than the map that was originally posted.  Same deal for the GEPS.  

[Carvers Gap]

12z Euro at 300.  This will 100% change, but this is an example of what "could" occur if a cold front drags its heels in the Gulf.

 

[Carvers Gap]

Here are the d10-15 or d11-16 500 anomaly comparisons from the big four ensembles...Heights over Greenland are rising.  BN heights over the SE.  EPO/PNA ridge.  BN heights over Alaska.  It is correct that BN heights over Alaska don't teleconnect to BN heights over the SE as a general rule. But old school winters would have a cold Alaska and cold Southeast with an almost continuous cold feed from the Yukon into the Ohio Valley.  It isn't without precedent, but recent climo is more or less against it.  Interestingly, on the GEFS, the BN heights over Alaska are temporary and maybe on one other ensemble.  Either way, that is a pretty decent cold signal for the first half of December.  I won't rule out a big ridge rolling through for a few days.

 

[housemtnTN]

Bring on the snow!

[Daniel Boone]

1 hour ago, Carvers Gap said:

I am waiting on the 12z EPS to fully populate so I can grab 5 and 10 day maps of 500 anomalies.  But here is the deterministic d10-15.   NAO and EPO regions both look good.

That's what we need. 

[Matthew70]

2 hours ago, Carvers Gap said:

I should add that climatology kind of doesn't like snow during early December in the valleys.  But during the last 15 years, it has allowed for it.  Anyway, this was the GMON from yesterday.  22 days in phase 8!

It can park there for all of January & February if like.  

[Matthew70]

2 hours ago, Carvers Gap said:

One more thing in a flurry of posts, I am beginning to see evidence that the NAO may begin to fire.  It is notoriously hard to predict, but it is significant in both the CMC and Euro 12z runs.  It is very evident on the 12z EPS and to some extent the 12z GEPS.  That is a BIG difference between the CMC/Euro vs GFS.  

Keep the flurry of posts coming.  When your on a flurry it says good things usually is being shown on the models! 

[*Flash*]

24 minutes ago, Matthew70 said:

Keep the flurry of posts coming.  When your on a flurry it says good things usually is being shown on the models! 

Truth. A hot thread during winter is generally a great thing! 

[Carvers Gap]

This kind of feels like one of these patterns where the warm pattern sits at about d13-15 and holds for a while.  Models really want to rush through the cold phases of the MJO, and that often ends up being an error.  It really looks like it wants to take its time.   Modeling was about 7-10 days too fast w/ the cold snap, and likely will be similar when we flip back warm.  I mean at some point during a La Nina winter, that trough has to slide into the Mountain West, right?  OTH, there is some brainstorming that this pattern is starting to show some Nino tendencies.  We do NOT want a La Nada in E TN.  Weak ENSO(Nada or Nino) is preferred.  

The Euro Weeklies look good for most of December.  They do show the trough eventually backing West, but that likely happens due to normal pattern cycles as well.  Here is the kicker...if that SSW finally works its way into the TPV, that warmup might not be real.  There is a risk of a double dip cold snap.  Nina climatology(cold December) + early season SSW (cold early and/or mid Jan) is on the table.  I do not think modeling even remotely has this pattern modeled well.  The -NAO on the 12z suites was prominent.  If that deal is real, things could get really squirrelly.  

I will be really surprised if we don't have something to track very soon.

[Carvers Gap]

 

[Carvers Gap]

The 18z GFS does not have this.  But here is the 18z RGEM at range. I think the GFS is a bit too amped.  The RGEM might be a little over done in Middle TN, but time of day is crucial.  This is basically a midnight to 1:00AM onset.  

 

[Carvers Gap]

The 18z GFS is right along the Ohio River Valley w/ the southern edge of the system.  I could make a good case for either result.  Climatology tends to support the northern track, but it really depends on how strong the high is over the top of this system.

[Carvers Gap]

1 hour ago, Matthew70 said:

Keep the flurry of posts coming.  When your on a flurry it says good things usually is being shown on the models! 

Haha.  Let's hope so.  I try to post in snippets as I have found over the years that those are easier to read than the essay posts - which I still use.  In other words, I think it is easier for folks (most of us are used to social media posts which are shorter) to ready the shorter posts.  Plus, sometimes I will have a big post which is "in process" as I look at model suites...and then it gets lost due to a refresh or any number of user errors.  Plus, I can delete an inaccurate or poorly worded "shorter" post and not lose an entire train of thought.

Truly, it is a lot more fun when everyone else is posting.  I like that the most by a long shot.  I think that is when our forum is at its best.  When it is quiet over the holidays or weekday mornings...sometimes I will post more.  But you all make the place what it is.

[jaxjagman]