December 2025 Short/Medium Range Forecast Thread

[Carvers Gap]

One last comment about the 12z suite…when looking at the ensembles, be sure to look at the number of solutions depicting a certain solution.  The warmer options are skewing the mean drastically when the median would look quite different.  This recently occurred with early December. 

[Daniel Boone]

2 hours ago, nrgjeff said:

Snow for Hanukkah. Severe for Christmas. Checks out!

Getting off my torch horse.. The following teleconnections reveal something like the chart below Days 16-20 which is Christmas and the following weekend. Maybe delay to New Year. Maybe the other way, shallow cold airmass brings a colder verification in Tennessee. Who knows?

Cold air supply in Canada
MJO tracking back through 7-8 colder phases
WPO ride still rex blocking North Pac, if we can boot any Alaska trough
Strato is still active / warm

Do not share for any commercial purposes. This was posted yesterday afternoon, so I feel like it's OK to share just here.

As usual, got some decent Year's snow wise but some not so good as well. One great one (2011) One terrible (1990) . 

[Carvers Gap]

Temps are 48, but the wind chill is 34 in this howler.  Absolutely freezing my tail off.

[Carvers Gap]

On 11/21/2025 at 4:27 PM, Carvers Gap said:

The flip has been quick!  The trend has not been our friend, but it is only November and we have just begun to fight...or something like that.

The pivot away from BN heights over Tenn Valley has voluminous support both in width and depth in the model world.  From ensembles to Weeklies....the trend is towards a standing wave SER over the SE.  It can be beaten down, but it immediately returns.  

Outlier models such at the Euro AIFS and GEPS persist.  I don't discount those.  If cold is coming, the Canadian model will see it first.  What we really want to see is the GFS deterministic to start bringing cold eastward OR the Euro control weeklies.  That Weeklies Euro control is a nifty tool.  With the exception of a few days earlier this week, it simply refused to be cold for December.

The repeated troughs into the Southwest are an ominous look if you like snow and cold.  I keep asking myself this question, "Have I been burned more by Baja lows which actually formed...OR have I been burned more by modeling which erroneously (due to feedback) put that feature in the Southwest?"  I guess we will find out soon!  Modeling often performs so poorly over that region.

I find it pretty hard to believe that the MJO in phase 8 is going to end up being warm.  So, I do think there will be some moderation(from AN heights) back towards seasonal and maybe even BN heights at some point for a 7-10 day period during December.  The Euro Weeklies today are cold at the surface, but I now think that is a bad, bad bias(and a new one at that) and an error.  Its 500 heights are now pretty much AN for most of December.  That would imply cold will push some, but the SER is the base pattern.

Again, this is shoulder season, and trends will likely still change - we can hope, right?!  However, for me anyway, my hopes that models are delaying the cold diminish with each passing run.  The reality is that it might not come to pass for much of December.  But it only takes one memorable snowstorm to make folks forget a warm pattern!  Besides, we usually don't get a lot of tracking in the valleys until January or Feb.  

We aren't even gonna talk about the retrograding BN heights(over the HB) into the West to start January!  If LR ext modeling was wrong about December cold, it could certainly be wrong about a January pattern at range!  I wish I had better news.  I will give it a few more days, and then I will almost certainly have to adjust my winter ideas.  

Have a good weekend, everyone!  At least we are getting some much needed rain.

I posted this on Nov 21st about the first and second weeks of November.  Look at the second paragraph.  That standing wave was replaced by a trough.  Is that standing wave over the SE a feedback error on the EPS and Euro?

[Daniel Boone]

21 minutes ago, Carvers Gap said:

I posted this on Nov 21st about the first and second weeks of November.  Look at the second paragraph.  That standing wave was replaced by a trough.  Is that standing wave over the SE a feedback error on the EPS and Euro?

It's beginning to look like it. 

[Daniel Boone]

39 here now with lt rain. It was snowing on Stone Mountain at 2500ft and up. As well as Wallen Ridge just south of Pennington gap at around 2800ft awhile ago when the band of Precip was heaviest.

[Matthew70]

The wind and windchill here definitely stings.  The sun went away quickly this morning..

Sunday afternoon that windchill is going to absolutely be brutal.

 

[submariner]

On 12/8/2025 at 6:07 PM, Carvers Gap said:

Really, the pattern right now is cold, reload, and more cold.  That might end later in December.  

44 degrees in Maryville and we just had some ice pellets bigger than peas. 

[Carvers Gap]

18z GFS....good run.  

[Jed33]

5 minutes ago, submariner said:

44 degrees in Maryville and we just had some ice pellets bigger than peas. 

A heavy sleet band just plowed through I mean just smoked us! Only problem was it only lasted for about a minute or so. It was cool while it lasted. Tried to coat the walkway and grass. The temp fell from 40 to 38 during the time. That was unexpected, at least by me!

[Matthew70]

1 hour ago, Carvers Gap said:

18z GFS....good run.  

I like hearing cold is staying around 

[John1122]

Snow is falling here currently. Very light. MRX did just put out an SPS that isolated 1 to 2 inch totals are possible. Currently 36 degrees. I was in Knoxville all evening so no idea what may have happened while I was gone. Except strong winds have blown some stuff around. 

[Daniel Boone]

43 minutes ago, John1122 said:

Snow is falling here currently. Very light. MRX did just put out an SPS that isolated 1 to 2 inch totals are possible. Currently 36 degrees. I was in Knoxville all evening so no idea what may have happened while I was gone. Except strong winds have blown some stuff around. 

Same here. 34.8 Degree's as of 9:35 PM

[John1122]

Looks like some decent snow showers moving across SE Kentucky, as with every single event in December, I'm likely too far west unless radar just isn't picking up anything NW of me, but basically SE Kentucky, Claiborne and points East may be in good shape if the Cumberlands don't dry those out.

[louise.caison233]

On 11/21/2025 at 11:27 PM, Carvers Gap said:

The flip has been quick!  The trend has not been our friend, but it is only November and we have just begun to fight...or something like that.

The pivot away from BN heights over Tenn Valley has voluminous support both in width and depth in the model world.  From ensembles to Weeklies....the trend is towards a standing wave SER over the SE.  It can be beaten down, but it immediately returns.  

Outlier models such at the Euro AIFS and GEPS persist.  I don't discount those.  If cold is coming, the Canadian model will see it first.  What we really want to see is the GFS deterministic to start bringing cold eastward OR the Euro control weeklies.  That Weeklies Euro control is a nifty tool.  With the exception of a few days earlier this week, it simply refused to be cold for December.

The repeated troughs into the Southwest are an ominous look if you like snow and cold.  I keep asking myself this question, "Have I been burned more by Baja lows which actually formed...OR have I been burned more by modeling which erroneously (due to feedback) put that feature in the Southwest?"  I guess we will find out soon!  Modeling often performs so poorly over that region.

I find it pretty hard to believe that the MJO in phase 8 is going to end up being warm.  So, I do think there will be some moderation(from AN heights) back towards seasonal and maybe even BN heights at some point for a 7-10 day period during December.  The Euro Weeklies today are cold at the surface, but I now think that is a bad, bad bias(and a new one at that) and an error.  Its 500 heights are now pretty much AN for most of December.  That would imply cold will push some, but the SER is the base pattern.

Again, this is shoulder season, and trends will likely still change - we can hope, right?!  However, for me anyway, my hopes that models are delaying the cold diminish with each passing run.  The reality is that it might not come to pass for much of December.  But it only takes one memorable snowstorm to make folks forget a warm pattern!  Besides, we usually don't get a lot of tracking in the valleys until January or Feb.  

We aren't even gonna talk about the retrograding BN heights(over the HB) into the West to start January!  If LR ext modeling was wrong about December cold, it could certainly be wrong about a January pattern at range!  I wish I had better news.  I will give it a few more days, and then I will almost certainly have to adjust my winter ideas.  

Have a good weekend, everyone!  At least we are getting some much needed rain.

The pattern looks messy, but there’s still time for shifts. One good storm can flip the mood fast, so I’m not giving up hope yet.

[John1122]

Got a dusting of snow, had a couple of decent showers. 31 degrees. 

[Holston_River_Rambler]

 

URGENT - WINTER WEATHER MESSAGE, HOLSTON'S WEATHER EMPORIUM, Mossy Grove, TN 6:30 AM EST

****YE OLDEN CLIPPER WARNING***

* WHAT...Light to occasionally moderate snow. Snow accumulations 1 to 4 inches, greatest across higher terrain. Winds gusting as high as 7 mph will produce pretty sights.

* WHERE...Eastern KY, SW VA, and possibly Bristol, TN and Mountain City, TN The greatest additional accumulations will focus across the higher terrain of the High Knob and peaks on the KY and NA border above 2500 feet.

* WHEN...Starting late this evening

* IMPACTS...Plan on some snow covered and slippery road conditions as well as the comfortable ease of a clipper's accumulations. Hot chocolate is recommended for these trying times.

SUMMARY...SW VA and eastern KY is in danger of getting hit by the first traditional clipper to hold together all the way to the southern Apps region in what seems to me like 7.5 million years. Some of the Hi Res models clip extreme NE TN too. 

Pretty much all the Hi Res models show the same thing, even the ever stingy NBM. 

 

[Carvers Gap]

3 hours ago, louise.caison233 said:

The pattern looks messy, but there’s still time for shifts. One good storm can flip the mood fast, so I’m not giving up hope yet.

That post was from November 21st as an example of how quickly things changed(back to cold) in modeling.  I was commenting at the time about a standing wave which never materialized in reality.  

I will have some comments hopefully this morning about the possible upcoming pattern change to a ridge over the East.  And yes, I do think it is probably a pattern change which will last through the last ten days of December and through most of January....but that isn't a slam dunk just yet, but more of a strong likelihood.

[Jed33]

Picked up a nice dusting here at the house overnight and actually saw more in town as I drove in to work this morning. Guessing there was maybe 1/2in or so at one point during the night here in town just judging by what’s left on rooftops and grass.

[John1122]

The MJO has indeed been in Ph 6 for a few days now. Hopefully it doesn't stay long. I suspect it's behind the massive warm ups we keep seeing modeled. Either way, the forecast looks bleak in the long range again. Not that it has been spectacular for our area really. 

[Carvers Gap]

I had a long post and basically just dumped it...too long.  The 12z GFS looks like it has an infinite loop which has crept into it(and other models) yet again.  This time it is over the PAC NW and front range of the Canadian Rockies.  Until that gets worked out, modeling is probably wrong.  I don't understand how that feedback loop is making its way into all modeling(reference early December fiasco).  Now, it could be right.  However, when we see a vortex continue to spin up in the same place over and over....you probably have found an infinite loop.

The 12z GFS shows what happens(late in the run) when the model exits the loop.  If that loop isn't real, it will likely exit that loop much earlier in the period which is what happened in early December.

As for the MJO, to me it looks like phase 7 on the actual OLR satellite map for today w/ some elements in 3 and 4.  It is definitely flirting with 6, but the tops look brighter in 7 and even some in 8.  RMM1/RMM2 has the MJO index in low phase 8 with it bordering on 7.  It might be generous to have it in 8.  The problem w/ phase 6 is that there is generally always some type of convection over the MC all the time at this time of year.  

That said, the cold forecast for tomorrow and bitter cold for Sunday/Monday looks like a classic phase 8 look.  After that, we see either a pattern relaxation(if indeed that is an infinite loop) or a pattern change to a western trough(if the infinite loop is actually real).

A gradient look w/ cold trapped in Canada...I can buy that.  8-10 days of repeated vortices spinning up over the PAC NW...not so much.

[Carvers Gap]

One thing to add and I haven't looked at SSW maps today.  It has been my experience that when we see a big WAR(western Atlantic ridge for the new folks), that ridge often precedes significant SSW events, especially if the ridge is anomalous.    That WAR will also often preceded HL blocking as well.  I don't have the lag on that, but I would guess 2-3 weeks and the bottom comes out.

[John1122]

It's just barely into 6, hopefully it's looping back towards 7,8. The beautiful pass through 8-1 the models had could have been great. It made it there (to 6)  a few days ago and models started blowtorching the lower 48 around that time. Which is basically phase 6 in a nutshell in winter. Hopefully Canada doesn't get scoured of cold. The snowpack north of us will likely be gone by Christmas if modeling is correct. I'm ready for a reset anyway, I think winter will make a comeback some time in January, unless we go full 1989-90. 

[Daniel Boone]

The MJO is basically a spread out cluster or clusters if you will. It not being very defined in a single area is making it's effects on the Pattern harder to pinpoint. Forcing is at a wider Area so to speak. If that consolidates into 8 later in the Month , or whatever phase, that typical Phase outcome should become most evident providing Other Driver's don't overpower it, imo. 

[John1122]

The main thing we can hope for is the shake-up isn't 6+ weeks, and that whatever happens after that, the Pacific is more favorable going forward. The current pattern is the Ohio Valley dream, and the Central Virginia snow globe, while we get stray flakes and glancing dustings. If Pacific had been a little more cooperative we'd have been clippered to 10+ inches by now. 

[Daniel Boone]

2 minutes ago, John1122 said:

It's just barely into 6, hopefully it's looping back towards 7,8. The beautiful pass through 8-1 the models had could have been great. It made it there (to 6)  a few days ago and models started blowtorching the lower 48 around that time. Which is basically phase 6 in a nutshell in winter. Hopefully Canada doesn't get scoured of cold. The snowpack north of us will likely be gone by Christmas if modeling is correct. I'm ready for a reset anyway, I think winter will make a comeback some time in January, unless we go full 1989-90. 

Yeah, COD heading toward six looks like on the Chart and that was the 8th so, extrapolating that course would be coming into six now. Sat Imagery as Carvers alluded looks rather undeterministic irt where really.

[Daniel Boone]

If it does like last time, it may even touch five and then crawl through 6. That would probably be a Months worth of crap for us if Blocking doesn't mitigate it.

[Carvers Gap]

Is that a different RMM1/RMM2 than CPC uses?  I noticed it is ABM generated.  I haven't seen the CPC site go into 6, and it is updated to the 11th.  Here is the CPC site's for today.  It never crosses into 6.  If they are different, I wonder which is more accurate.

Now, back to model feedback, and the 12z GFS was EXTREME with it today.  I figured that if was noticing at 500, the surface had to be crazy.  This is a comparison of the AIFS and GFS at 12z.  Notice anything?  This is how we know that we are dealing with model feedback, OR the ski slopes in the Sierra Nevada are about to get buried(not without precedent BTW).

 

[Carvers Gap]

Until that feedback gets fixed, things are not going to be right.  I think we see one of two things happen.  Either a trough sets up shop in the West or that trough kicks out and models correct.   I just don't know.  But I do know this...either the AIFS or GFS is off its rocker.

[John1122]

25 minutes ago, Daniel Boone said:

Yeah, COD heading toward six looks like on the Chart and that was the 8th so, extrapolating that course would be coming into six now. Sat Imagery as Carvers alluded looks rather undeterministic irt where really.

The forecasts are still mostly favorable for it, but they are all starting it a little off where it actually is now by the look of it. Sadly, even with the favorable forecasts we still manage to get warm on models. Not sure if it's a headfake by them or if it's the MPNA from the paper I linked last month, that says 8 isn't cold of the MPNA is negative.