December 2025 Short/Medium Range Forecast Thread

[jaxjagman]

4 hours ago, Carvers Gap said:

Someone remind me…the SOI tanking means a potential bigger winter storm, right?  Strong amplification incoming and stormy.

Be a good case study upcoming in general cause around the 23rd of Nov the SOI dropped,and took out the Nina base state but rose shortly afterwards back towards NINA,so you'd have BN temps towards the middle of Dec but this would be transient because afterwards a few days the SOI would rise again.But the large fall the last few days would tell you it could get rather cold right before X-Mas unlike some of what the models seemingly show,but other teleconnections still play apart

[jaxjagman]

Ill use what the EPS shows,as heights rise into East China/Koreas this should be a warming in the east,BUT during this time the blocking along the Aluetians get shifted into Siberia,this would cause height falls into East Asia,i really think we will have a cold X-Mas,plus the MJO into which seems TO to be maybe in Africa right now maybe or at least western IO

 

[jaxjagman]

But you should see a definite warm up past the Mid of Dec,probably not brutal but AN

[Holston_River_Rambler]

Interesting to see the trend for more return flow moisture for the Sunday night into Monday system on the GFS

 

If anything the Euro is getting dryer 

 

It still has a little slug of moisture over S Alabama and eastern Georgia, but it doesn't really make it north. 

To be honest my choice to use 700mb is arbitrary, but is the place I see the biggest difference between the GFS and Euro on relative humidity panels:

 

 

the 500 mb vort seems slightly more amped on the GFS, but not by much. 

 

 

NAMs and RRFS (thanks John for the heads up about ol Rufus) emphasize a second shortwave connected to the above, dropping in and enhancing upslope without much fanfare for the first shortwave the GFS likes.  Here is Rufus and teh second shortwave in all Rufus's pixilated glory. 

 

 I suspect the GFS is wrong about the first shortwave, since even the NAM in NAMing range isn't too interested, but could be nice for elevation areas in NE TN, SW VA, and especially Western NC if not. 

I think Carvers pointed out a run of the GFS yesterday that had like 6" in portions of that area. 

[Holston_River_Rambler]

Some ensemble interest on the GEFS for Sunday night into Monday morning:

 

As expected, Euro, not so much:

 

[*Flash*]

20 hours ago, Carvers Gap said:

Someone remind me…the SOI tanking means a potential bigger winter storm, right?  Strong amplification incoming and stormy.

Yeah, that SOI sauce be crazy. As some have mentioned, the devil is in the latency of effect, but to what gives us stronger amp, we should generally root for. On an unrelated note, what are our thoughts on the second half of winter? I got one more bag Fry set to arrive on 12/17/25 so I'll be grounded from chasin' for 6 weeks (wife can't drive post c-section). Come Groundhog's Day, I'll be able to get back on the road and potentially bring my 10-year-old with me. 

[Matthew70]

2 hours ago, *Flash* said:

Yeah, that SOI sauce be crazy. As some have mentioned, the devil is in the latency of effect, but to what gives us stronger amp, we should generally root for. On an unrelated note, where are our thoughts on the second half of winter? I got one more Bag Fry set to arrive on 12/17/25 so I'll be grounded from chasin' for 6 weeks (wife can't drive post c-section). Come Groundhog's Day, I'll be able to get back on the road and potentially bring my 10-year-old with me. 

Congratulations to the you & your wife on the next little one! 

[jaxjagman]

2 hours ago, *Flash* said:

Yeah, that SOI sauce be crazy. As some have mentioned, the devil is in the latency of effect, but to what gives us stronger amp, we should generally root for. On an unrelated note, where are our thoughts on the second half of winter? I got one more Bag Fry set to arrive on 12/17/25 so I'll be grounded from chasin' for 6 weeks (wife can't drive post c-section). Come Groundhog's Day, I'll be able to get back on the road and potentially bring my 10-year-old with me. 

Congrats bro !!

[Daniel Boone]

Congratulations !

[jaxjagman]

Ensembles are going Zonal in the long range,not a warm look but its not cold either,very little QPFS,probably the only hope would be a bowling ball if it could manifest any cold with it

I'm starting to wonder if the CFS is more right with the RMM'S,its been showing it going into WP the last several days,now its showing another Kelvin,Rossby into the WP towards the end of the year and crapping out there,we'll see if it keeps showing this.

[John1122]

The GFS is just ridiculously cold and dry as a bone. Shades of December '83 all over again.

[Matthew70]

Definitely some cold air for next weekend.  If we could just get an Alberta clipper to swing thru. Below average December looks to continue for the next 2 weeks

[Matthew70]

Just now, John1122 said:

The GFS is just ridiculously cold and dry as a bone. Shades of December '83 all over again.

Hopefully some clippers get into the flow. 

[jaxjagman]

Sure looks like the MJO is getting into the IO/Maritime

10 minutes ago, John1122 said:

The GFS is just ridiculously cold and dry as a bone. Shades of December '83 all over again.

No doubt about that,,big Artic High moving down from the Upper Plains

[Carvers Gap]

Apparently, I just need to miss the 12z suite for all **** to break loose.  Shiver me timbers, GFS w/ a piece of the TPV!  Storms on the Euro.  

[Daniel Boone]

So far the truly cold air hasn't been making it into the Great Valley this Month. You can see how it fell down west and East of the Great Valley in the Month T Plot. It's in the 40's Today. That falls within Average for here. This Mornings Low was above Average due to being socked in with Fog and low St Deck.  Yesterday was near Normal as far as daily goes. The point being, although much of the East( MW, Oh Valley, NE and MA have been very cold, our Area and Southeastward hasn't in comparison.

     Qustion to debate is, the Reason why?. I'd like to see what everyone can come up with and get a common denominator . Mine is no strong Hp press down western slopes of Apps. Then there has been the residual heat Sourh of us left over from the Cuban HP that weakened and moved on SEward that pulls up toward the Jet and mixes. 

      If Modeling is correct showing the strong HP coming down from Canada into the Plains we will be in the Icebox as well as we all know.

[Carvers Gap]

I just think climatology really doesn't support super cold air until mid-December.  There are lots of "whys," but I also think the MJO wasn't in the phase where the cold centers in southeastern NA.  But it is MUCH colder than models had it when the SER was once modeled here w/ highs in the 70s.  IMHO, modeling has tended to have a shallower trough and that has verified.  The bitterly cold air I have seen modeled has been w/ the cold air masses of Dec 8th and 14th.  

And to the number that matters, TRI is -6.8F for the month so far.  That is pretty big departure.  Every day has been BN w/ a trace of snow on two of the six days.  I can say this...I have been freezing my tail off while running in the mornings.  I pretty much ice skated one morning on freezing fog.  Pretty good start in my book.

[Carvers Gap]

The other thing I am noticing is an uptick of the mean snow total over TRI.  That might be "IMBY" a bit too much, but that is usually a good thing for everyone when it goes up.  The 12z AIFS-Ensemble has 2-5" of snow from TYS to SW VA.  The 12z GEFS has 1-6" of snow from TYS to TRI.  

[John1122]

43 minutes ago, Daniel Boone said:

So far the truly cold air hasn't been making it into the Great Valley this Month. You can see how it fell down west and East of the Great Valley in the Month T Plot. It's in the 40's Today. That falls within Average for here. This Mornings Low was above Average due to being socked in with Fog and low St Deck.  Yesterday was near Normal as far as daily goes. The point being, although much of the East( MW, Oh Valley, NE and MA have been very cold, our Area and Southeastward hasn't in comparison.

     Qustion to debate is, the Reason why?. I'd like to see what everyone can come up with and get a common denominator . Mine is no strong Hp press down western slopes of Apps. Then there has been the residual heat Sourh of us left over from the Cuban HP that weakened and moved on SEward that pulls up toward the Jet and mixes. 

      If Modeling is correct showing the strong HP coming down from Canada into the Plains we will be in the Icebox as well as we all know.

To me, it's the shape of the ridge in the West. It's not been sharp S to N oriented so the cold hasn't been pressing south, more West to East. The GFS sharpens the Western Ridge and the cold crashes south. 

[Carvers Gap]

I am just now catching up on overnight and afternoon modeling, so please forgive me if I am on stepping in old footprints.  These are the real feel temps for the mid-month cold front.  The GFS I "think" had this on d16 of its run a few days ago.  It is now well within d10.   The 12z EPS is the colder of all the ensembles, and that gets my attention w/ its usual warm bias.  Some deterministic models don't get us above 20 degrees.  

This reminds me of the 09-10 setup.  It got cold right as school let out - as in the very day school was dismissed for Christmas.  Cars were stranded in a pretty good commuter snow storm.  This could be an 83-84 deal where it gets cold and doesn't snow. I fully see that.  However, I see the Euro cranking a big storm high around this time frame.  Often, we will see cold temps and big snows coupled.  These temps are pretty much on bare ground.  The GFS gets TRI below zero(in some places) with actual temps.

The thing that concerns me a bit is that the GFS has the warmest MJO!!!  If it is just now catching on(and it has a habit of seeing cold shots before other models at range during December), then look out.  

Still time for things to change, but a big shot of cold air is growing likely but not certain.  Once we get to day 6-7, I think the cold is baked in the cake...so a few more runs to go.  

TRI has managed -6.8F and TYS -7F(for the first six days of the month) without strong amplification.  What I am seeing w/ deterministic runs is a tendency to amplify the pattern sooner than later.

 

[John1122]

We are -8 for the month, but normally you arrive there by being -16 and then normal over short periods. This has been essentially-7 to -10 each day, so nothing super cold. 

[Carvers Gap]

With the potential or much colder temps this month, and a tendency not to soar way AN....we could be looking at a top 10 cold month for TRI.  I'll have to go check and see...but that is off the top of my head.  7 day ensembles for mid month are -10 to 15F BN

[Carvers Gap]

Since 1980, the only month I can find w/ a faster(low max temp) start is 1985.  Here is the Dec 1-4 data for 2025.  These are the max temp departures.  As Boone noted, overnight departures are not as strong.  I have to think that is due to a lot of fog and cloud cover.   I'll update w/ more recent numbers when this updates again.

***updated w/ reference maps of max AND low temp compositees***

 

 

 

 

 

[Carvers Gap]

Here is the average(lows and highs) for December through the 4th.  I will go back up and post the map(with the reference years above...give me a sec to edit that one)...

1985, 2000, 2010, and 2024(almost the same start) are very similar or colder to 2025.  But that is about it.  

[Carvers Gap]

1 hour ago, Daniel Boone said:

So far the truly cold air hasn't been making it into the Great Valley this Month. You can see how it fell down west and East of the Great Valley in the Month T Plot. It's in the 40's Today. That falls within Average for here. This Mornings Low was above Average due to being socked in with Fog and low St Deck.  Yesterday was near Normal as far as daily goes. The point being, although much of the East( MW, Oh Valley, NE and MA have been very cold, our Area and Southeastward hasn't in comparison.

     Qustion to debate is, the Reason why?. I'd like to see what everyone can come up with and get a common denominator . Mine is no strong Hp press down western slopes of Apps. Then there has been the residual heat Sourh of us left over from the Cuban HP that weakened and moved on SEward that pulls up toward the Jet and mixes. 

      If Modeling is correct showing the strong HP coming down from Canada into the Plains we will be in the Icebox as well as we all know.

And a great question I might add.  A great question is always better than a great answer....The more I think about it, the more I think it is because they have more snow cover right now.  The trough is just a tick too far to the East right now as well.

[Daniel Boone]

39 minutes ago, Carvers Gap said:

I just think climatology really doesn't support super cold air until mid-December.  There are lots of "whys," but I also think the MJO wasn't in the phase where the cold centers in southeastern NA.  But it is MUCH colder than models had it when the SER was once modeled here w/ highs in the 70s.  IMHO, modeling has tended to have a shallower trough and that has verified.  The bitterly cold air I have seen modeled has been w/ the cold air masses of Dec 8th and 14th.  

And to the number that matters, TRI is -6.8F for the month so far.  That is pretty big departure.  Every day has been BN w/ a trace of snow on two of the six days.  I can say this...I have been freezing my tail off while running in the mornings.  I pretty much ice skated one morning on freezing fog.  Pretty good start in my book.

I guess I still go by 1980 to 2010 Averages more. The Avgerages have really jumped over the year's and the thing is that's not always caught is the last sevral Year's that jump is added on in the NWS Station Avgs. The Avg high for Pennington gap this Date was 47 Hi 27 low in 2010 I think. So, average is running below that for the balance but not extreme( however, I think that has gone up some now). KTRI  now says the Average high there is like 51 or so Low 31 I think. That's several degrees milder than used to be for there.  

So, with "Today's" Averages we're running a good bit below. the point basically being the difference in comparison to our west and East. There is a Spike through here of not of below as the aforementioned. I think John actually hit it with the western Ridge Height as far as the point being addressed. 

    I see your reasoning though as the cold we have got has been constant. Of which is a rarity, especially this early.

      

[Carvers Gap]

7 hours ago, Holston_River_Rambler said:

Interesting to see the trend for more return flow moisture for the Sunday night into Monday system on the GFS

 

If anything the Euro is getting dryer 

 

It still has a little slug of moisture over S Alabama and eastern Georgia, but it doesn't really make it north. 

To be honest my choice to use 700mb is arbitrary, but is the place I see the biggest difference between the GFS and Euro on relative humidity panels:

 

 

the 500 mb vort seems slightly more amped on the GFS, but not by much. 

 

 

NAMs and RRFS (thanks John for the heads up about ol Rufus) emphasize a second shortwave connected to the above, dropping in and enhancing upslope without much fanfare for the first shortwave the GFS likes.  Here is Rufus and teh second shortwave in all Rufus's pixilated glory. 

 

 I suspect the GFS is wrong about the first shortwave, since even the NAM in NAMing range isn't too interested, but could be nice for elevation areas in NE TN, SW VA, and especially Western NC if not. 

I think Carvers pointed out a run of the GFS yesterday that had like 6" in portions of that area. 

It is back to 6" for portions of Sullivan Co on the 12z today.  The AIFS has 1-3".  I still think it is over done, but the GFS can sometimes score a weird coup from time to time.  For now it is an extreme outlier.  I wouldn't be surprised for NW facing slopes to see 1-2" out of that system tomorrow night.

[Daniel Boone]

9 minutes ago, Carvers Gap said:

And a great question I might add.  A great question is always better than a great answer....The more I think about it, the more I think it is because they have more snow cover right now.  The trough is just a tick too far to the East right now as well.

Yes, that's another reason that makes sense. I was actually wondering earlier today if the wind shifted to the NW that even without a frontal passage our Temp would fall due to upstream snowcover.

[Carvers Gap]

6 hours ago, *Flash* said:

Yeah, that SOI sauce be crazy. As some have mentioned, the devil is in the latency of effect, but to what gives us stronger amp, we should generally root for. On an unrelated note, what are our thoughts on the second half of winter? I got one more bag Fry set to arrive on 12/17/25 so I'll be grounded from chasin' for 6 weeks (wife can't drive post c-section). Come Groundhog's Day, I'll be able to get back on the road and potentially bring my 10-year-old with me. 

Congratulations, man!!!  I just now saw this.

Second half of winter is a toss-up for me.  I tend to think the pattern we see right now will repeat and/or be very hard to break down.  If this was an amplified pattern, I think it breaks down quickly.  But these flatter wavelengths are gonna make it tough to budge.  Cosgrove likes a backloaded winter and has sound analysis to back it up.  I am gonna roll with 95-96 light.  That would mean a cold start followed by a warmup which is followed by the worst of winter per Cosgrove.  Now, that runs against my seasonal ideas, but it sure looks like that is on tap.  My original ideas are winter in December followed by a gradual warm-up for Jan-Feb.  I may still get that if December goes in the tank, ie Jan-Feb would almost have to be warmer against the norms.  But Jan and Feb could be colder than my original ideas.  

The big thing for me is that the coldest air on the planet is here and in Asia.  Our source regions have been lacking in recent years, but not this year.  With the QBO at -25.35 for November(and an unexpected drop after what appeared to be the plateau before it rises), it sure looks like winter still has some life in it for Jan-Feb...I would guess the NAO is about to fire up.

These strat warming episodes could very well make for some cold mischief during January.

[jaxjagman]

Record low on Deb 14 in Nashville was 6 degrees back into 1917,so that would break our record if it were to be correct