December 2025 Short/Medium Range Forecast Thread

[Carvers Gap]

The 12z AIFS pushes back pretty heavily on the chinook - even more so than the 6z GFS.   Take one look at the 500 map, and it doesn't look great.  But take a look at what is creeping into Greenland.  That is a game changer if it stands(and doesn't connect to a WAR).

 

But take a look at the surface.  Not what you would expect.  That isn't warm.  Cold air is seeping into the EC.  A cold hp over the GL is not a bad thing for us. FWIW, the 12z GFS looked ready to break the chinook look by the end of its run.  The NAO firing will force everything south.

 

[Matthew70]

1 hour ago, Daniel Boone said:

Thanks brother ! I hope and pray your Wife gets well and you stay healthy. Dr said Flu was bad here too. He said Covid was too but it's Symptoms haven't been as bad as the other Viruses.

Thank you!  Yes hopefully the flu shot will help me some if I get it.  Having the damaged lungs from Covid.  I need to avoid any flu.  I know vaccines can be a dirty word for many but I have to take any precautions I can. 

[Daniel Boone]

1 hour ago, Carvers Gap said:

The 12z AIFS pushes back pretty heavily on the chinook - even more so than the 6z GFS.   Take one look at the 500 map, and it doesn't look great.  But take a look at what is creeping into Greenland.  That is a game changer if it stands(and doesn't connect to a WAR).

 

But take a look at the surface.  Not what you would expect.  That isn't warm.  Cold air is seeping into the EC.  A cold hp over the GL is not a bad thing for us. FWIW, the 12z GFS looked ready to break the chinook look by the end of its run.  The NAO firing will force everything south.

 

That's the evolution of getting that pesky GOA Low moved. Force that sucker South and West . The Central Ridge gets forced back West from the classic blocking that looks to be setting up..if that 50-50 is real, that'll be the real deal blocking Pattern.

[BooneWX]

2 hours ago, Daniel Boone said:

Yeah. I still have this Upper Respiratory Virus. 12 days so far. Dr says it has now led to a Sinus and bronchial Infection. So, yeah would be a nice break with a mild period and more moisture in the air. Be careful out and about folks. Alot of nasty stuff going around. Dr even said the regular cold virus is stronger and harder to shake than usual.

I’ve got a kid in daycare and it’s been an absolute nightmare of viruses since September really. This fall and winter has been a sick season on steroids.

[Carvers Gap]

19 minutes ago, BooneWX said:

I’ve got a kid in daycare and it’s been an absolute nightmare of viruses since September really. This fall and winter has been a sick season on steroids.

Yeah, cold and viruses have been making laps in my crew.  Pretty miserable stuff and hangs on forever as @Daniel Boonenoted.  

Hopefully the 12z Euro Weeklies are right and we see cold return right after mid-January.  The 12z CFSv2 breaks for cold at about the same time.  

It looks like when the NAO fires(if it fires), that puts a clock on the chinook.  Maybe if that NAO can fire earlier, we can return to a colder pattern more quickly.  But really, I am good with a couple of weeks of warm weather.  Something makes me think the dam is gonna bust at some point sooner than later.  One good cutter, and it could all come south.

[Golf757075]

2 minutes ago, Carvers Gap said:

Yeah, cold and viruses have been making laps in my crew.  Pretty miserable stuff and hangs on forever as @Daniel Boonenoted.  

Hopefully the 12z Euro Weeklies are right and we see cold return right after mid-January.  The 12z CFSv2 breaks for cold at about the same time.  

It looks like when the NAO fires(if it fires), that puts a clock on the chinook.  Maybe if that NAO can fire earlier, we can return to a colder pattern more quickly.  But really, I am good with a couple of weeks of warm weather.  Something makes me think the dam is gonna bust at some point sooner than later.  One good cutter, and it could all come south.

I think a true pattern change will take place when the mjo starts to move. Takes a while to get out of warm patterns if they become established imo

[Carvers Gap]

That is a big time NAO on the 18z GFS run.  It doesn't have a lot of impact yet, and its staying power is TBD.  It may be a forced NAO which just results due to dynamics and is passing through, or it might be the SSW finally working its magic along w/ the QBO.  It could hook into the mid-continent ridge, but that generally would cause an NAO and subsequent cold outbreak about 3 weeks later...and has been a common feature of winters of late.

[Carvers Gap]

By 200, the NAO is having significant effects on the run compared to previous runs.  The 12z AIFS scores a coup if it nailed it first.

[Carvers Gap]

Wow.  If that NAO is real on the 18z GFS, it very well could force split flow...and you kind of see it at the end of this run.  That will completely upend modeling over the next few days if legit.  That would be a major player.  The 12z AIFS and 18z GFS now have this.

[Carvers Gap]

I think what we will see is the MJO slide into phase 6 as the NAO fires.  The mid continental ridge will hook into it briefly.  That will create a significant SSW.  The MJO will slide into 7-8 as the CHI charts showed over the weekend.  The entire cold air mass gets released into a full latitude trough over the US w/ the storm track south of the Ohio River Valley.  Good sign if it holds.  The NAO will work against us at first, but as it matures...that is when it pays off.

[Golf757075]

10 minutes ago, Carvers Gap said:

I think what we will see is the MJO slide into phase 6 as the NAO fires.  The mid continental ridge will hook into it briefly.  That will create a significant SSW.  The MJO will slide into 7-8 as the CHI charts showed over the weekend.  The entire cold air mass gets released into a full latitude trough over the US w/ the storm track south of the Ohio River Valley.  Good sign if it holds.  The NAO will work against us at first, but as it matures...that is when it pays off

Carver, that's good news if true! Op runs and ensembles will show a colder outcome if it's legit. If not, it won't imo.

[John1122]

Use with caution, but the CFS fired off a big -NAO and cold underneath a few days post Christmas. 

 

[Carvers Gap]

The 18z AIFS has a -EPO ridge at the end of its run.  A lot of this looks like SSW signals - hints of HL blocking.

[John1122]

That NAO depicted above really strengthens around Dec 28th on the CFS. 

[Daniel Boone]

1 hour ago, John1122 said:

Use with caution, but the CFS fired off a big -NAO and cold underneath a few days post Christmas. 

 

I saw where Bamwx is buying that Depiction. He's getting backlash of course. I recall the Winters when we got cold and Snow with a GOA Low in Place and that was how it was done. Systems would track NW to SE down the Jet . Sometimes Systems would traverse the STJ and phase in the lower Ms Valley. Those were the big ones if you got one in that Pattern. However, I recal some 3-6 inches with the Miller B and Clippers in that Pattern. 

[Daniel Boone]

3 hours ago, Carvers Gap said:

I think what we will see is the MJO slide into phase 6 as the NAO fires.  The mid continental ridge will hook into it briefly.  That will create a significant SSW.  The MJO will slide into 7-8 as the CHI charts showed over the weekend.  The entire cold air mass gets released into a full latitude trough over the US w/ the storm track south of the Ohio River Valley.  Good sign if it holds.  The NAO will work against us at first, but as it matures...that is when it pays off.

The MJO is what had me concerned when we were discussing modeling may be pushing back west gradually with the big warmth . If it does go six with a GOA Low it could possibly force a deep western Trough . May start seeing bowling balls down the west Coast and then move inland. If that's the case, you may be right about the NAO and it may hook with the Continent Ridge but, the good thing too is that's more rare than the NAO, SER Hookup. If the NAO is Central based, Greenland centered, it's doubtful any mid continent hookup. It may just force that Ridge west and cause it to sharpen between the far western Trough and back building Eastern one. That happened a couple of times in the late 80's and early 90's. . 

Rather Tricky setup to forecast coming up. Timing of these features is going to affect the Outcome considerably, imo.

[John1122]

I'm verifying much cooler than forecast lately. Last night my predicted low was 21, it was 15 this morning. Predicted high was 45, it was 41. Predicted low of 32 tonight, it's already 26. 

[Daniel Boone]

16 minutes ago, John1122 said:

I'm verifying much cooler than forecast lately. Last night my predicted low was 21, it was 15 this morning. Predicted high was 45, it was 41. Predicted low of 32 tonight, it's already 26. 

Are you in a mountain Valley in any way ? It's 35 here. There was snow still lying around up in Wise County today. Half inch to an inch in some shady areas in Norton and Wise . The  Temperature was near 40 there this Afternoon.

[John1122]

1 hour ago, Daniel Boone said:

Are you in a mountain Valley in any way ? It's 35 here. There was snow still lying around up in Wise County today. Half inch to an inch in some shady areas in Norton and Wise . The  Temperature was near 40 there this Afternoon.

Yes, I'm surrounded on all sides by 2500ft+ peaks.

[Carvers Gap]

Kind of wild in the wx model world at 0z and 6z.  The 6z GFS cuts into the Chinook lifespan fairs significantly.  IF the NAO is a realistic player, it is likely going to turn the pattern after 240 upside-down.  It sure did last night on several runs.

[Carvers Gap]

12z suite is rolling.  I am going to put my thoughts on this suite in this single post.  I will simply update it by editing.  Feel free to comment.  Just know this post is going to have several comments.  So, you might "like" one thing, and it might be followed by something you don't like.  Haha.

12z GFS

-The GFS is really the first model to correct the Pacific NW.  It has beens slowly doing this very several runs.  Let's see where this run goes.  I generally just toss the run if a slp wonders from British Columbia to 500 east of LA.  6z had a realistic solution.

-@ 132 the GFS is flirting w/ a winter event over SE KY, SW VA, and NE TN.  Probably is WAA, but tough to tell.  Interesting development which I don't think has been there before.

-The interesting thing is that there is a hp sitting over the top of that.

-@ 195  that looks like more feedback over the Pac NW.  Interestingly, there is an EPO ridge forming(temporary?).  Definitely seems like this timeframe is a demarcation between a good path back to winter weather and on that is not.

-@204 that storm off the coast of Cali looks like it might move inland.  Any storm that enters at the latitude of Los Angels has to be watched on the EC.  Many times a storm will enter and exit at similar latitudes of NA...not matter how far north our south they wonder while over the continent.

-@240 generally I just look at the long wave pattern as details are going to change by the next run.  The GFS got lost around 195...and ended up with a much different solution

-the Dec 22nd cold front is present w/ wintry precip on its northern edge as it departs...big take away and we'll see if it sticks.

-I should add that the -NAO is present on this run, but slightly less strong.  The NAO is very difficult for models at range, but can make big difference upstream if they form a block.

-As wild as that run got, it pretty much got to the same point that 6z did by 270.

-300+ The GFS puts the trough back in the East(temporary?).  The run-to-run change graphics for this time frame are gonna be fun - really fun.

-On both the GEM and GFS...the NAO is east based but having a major effect on the 500 upstream pattern of all of North America.  Right now, the GFS has a window from Dec 23-Dec30 for the chinook.  Then, recent deterministic runs tend to slam the door on that by the New Year.  The real fun begins is if the 6z GFS run blends w/ the 12z run at some point....chinook muted and then trough into the East.  Don't know if that can happen, but w/ the MJO in the COD, the SSW may be taking the driver's seat.  The NAO would likely be a result of that.

12z AIFS

-Looks remarkably similar to the GFS.  Looks like around 300 it wants to send a decently amplified trough eastward.  Not sure if that is temporary or not, but w/ the NAO sitting up top...that teleconnects to an eastern trough more times than not with the usual caveats mentioned by Boone and me in early posts.

[Carvers Gap]

The GFS and the GEM (if one extrapolates past 240) continue to tease some big changes just after d10.  The NAO is trying to be a player.  It backs up the entire flow upstream and basically resets the 500 chinook pattern.  Is it right?  IDK.  If we can get a storm to hit the West Coast near Los Angeles, that might do the trick in flipping the trough back East.

[Daniel Boone]

2 hours ago, Carvers Gap said:

The GFS and the GEM (if one extrapolates past 240) continue to tease some big changes just after d10.  The NAO is trying to be a player.  It backs up the entire flow upstream and basically resets the 500 chinook pattern.  Is it right?  IDK.  If we can get a storm to hit the West Coast near Los Angeles, that might do the trick in flipping the trough back East.

Yep. Still got the usual crowd in Enso forum going complete eventual mild takeover for the east into January. Don S. even. He may change his thoughts with the latest data on the NAO coming in stronger and backing west. They were sold on it being east based. Larry's having to set them straight with latest charts. I won't gloat though as, it's not set in Stone yet. 

[Carvers Gap]

1 hour ago, Daniel Boone said:

Yep. Still got the usual crowd in Enso forum going complete eventual mild takeover for the east into January. Don S. even. He may change his thoughts with the latest data on the NAO coming in stronger and backing west. They were sold on it being east based. Larry's having to set them straight with latest charts. I won't gloat though as, it's not set in Stone yet. 

GaWx has a nice run-to-run post about the 12z GEFS and how it started to lower heights over the NE in response to the NAO.  I have had the NAO wreck my ideas more than once(good and bad) both when it appeared suddenly or didn't appear as forecast.  It is a true wrecking ball.  Until models sort it out, proceeding with caution is wise.  I agree.

[Golf757075]

10 minutes ago, Carvers Gap said:

GaWx has a nice run-to-run post about the 12z GEFS and how it started to lower heights over the NE in response to the NAO.  I have had the NAO wreck my ideas more than once(good and bad) both when it appeared suddenly or didn't appear as forecast.  It is a true wrecking ball.  Until models sort it out, proceeding with caution is wise.  I agree.

Carver, I believe if the nao can become west based, we will be in better shape. Hoping we don't squander most of January on warmer than normal. Still need a pattern reshuffle to have a chance later imo

[Matthew70]

1 hour ago, Daniel Boone said:

Yep. Still got the usual crowd in Enso forum going complete eventual mild takeover for the east into January. Don S. even. He may change his thoughts with the latest data on the NAO coming in stronger and backing west. They were sold on it being east based. Larry's having to set them straight with latest charts. I won't gloat though as, it's not set in Stone yet. 

It’s truly unbelievable that people say they want snow, but they seem to be more happier with the warmer temps.  I call them trolls.  If winter is really over like they say, why are they even chatting in a winter forum?

[Matthew70]

22 minutes ago, Golf757075 said:

Carver, I believe if the nao can become west based, we will be in better shape. Hoping we don't squander most of January on warmer than normal. Still need a pattern reshuffle to have a chance later imo

There is going to be a  pattern reshuffle eventually.  As far as part of January being warm. We always have at least one week of warm weather in January. Also known as the January thaw.  Maybe we’re having it in December instead.  People need to remind themselves that the biggest snows for Tennessee usually occur in February. Especially for West and Middle Tennessee.

[Jed33]

3 minutes ago, Matthew70 said:

There is going to be a  pattern reshuffle eventually.  As far as part of January being warm. We always have at least one week of warm weather in January. Also known as the January thaw.  Maybe we’re having it in December instead.  People need to remind themselves that the biggest snows for Tennessee usually occur in February. Especially for West and Middle Tennessee.

I was just thinking earlier today, what if the January thaw that we normally get was displaced by a few weeks into December instead of January. Wouldn’t that be something! Now, don’t get me wrong, I’m not calling for that, nor do I even know if there’s any precedent for that. It’s just a thought I had. 

[housemtnTN]

36 minutes ago, Matthew70 said:

It’s truly unbelievable that people say they want snow, but they seem to be more happier with the warmer temps.  I call them trolls.  If winter is really over like they say, why are they even chatting in a winter forum?

I will say, I prefer the warm weather over cold, but since the weather is out of my control, and it's gonna be cold, then LET IT SNOW!!

[Carvers Gap]

The 18z GFS appears to have lost most of its feedback with BN heights coming over the pole at to crash into the eastern ridge.  The NAO bout to be tested this run.  Let’s see where it goes.  Just looking for consistent trends at this point and not random solutions.

-only minor feedback on the West Coast this run.  So far...

-at 300, that is a big time trough in bound...and a monster NAO

-Shortly after...the chinook pattern is gone.

- Basically, the Chinook has from Dec 24-29th to do its work.  It might be the most overtracked feature across forums in many years.  Turns out, this may well just be your standard warm-up after a cold spell.

-the mechanism is n place late in the run for a full latitude trough w/ trough wedged between an west Alaskan block and a Greenland block.  

-trough dives west at the end of the run, but almost certainly would have to kick east.  There is a little bit of feedback along the WC again.  If the trough dives through the front range and not along the coast....that would bring bitterly cold air into most of the country. 

-right now we can see modeling correcting away from feedback.  How do we know that?  Infinite vortices are not forming off the coast of Washington State.

-Important...what makes more sense it that a double block(omega) is forming(a bit non-traditional) in the medium and long range.  Energy is diving down the left side of the trough, gets kicked eastward, and the right side of the block slows down the energy and forces it north.  The Rex block has trouble forming(thorn in the medium range) as the NAO exerts force.  What I expect to happen is the NAO(if it is real) eventually forces an EPO or PNA to pop...ridge comes East.  That almost fits what I "think" will be the MJO rotation with a more sustainable eastern trough by roughly mid Jan give or take a week.  The NAO could speed up that transition...so it has to be watched.