December 2025 Short/Medium Range Forecast Thread

[Carvers Gap]

I haven't talked a ton about the d10-15 today, but modeling is MUCH colder with it.  The 18z GFS is frigid.  Its ensemble isn't much warmer.  The EPS at 12 was cold.  I think the MJO juice has made it to the deterministic models and their accompanying ensembles @Daniel Boone!  The juice is loose!

[Carvers Gap]

4 hours ago, nrgjeff said:

This system will probably do more than Monday night Tennessee north of I-40. Not everywhere, but more places esp northeast Tenn.

More I mean snow. Fortunately the ice looks trace again. Regrettably I don't have time to write more. Good luck up there!

You all are keeping the lights on which we appreciate greatly!!!!

[Daniel Boone]

4 hours ago, John1122 said:

It looked like Maine or somewhere here in 1996. There was snow piled up to the bottom of stop signs and in mountains in parking lots from Early January until around Valentines Day.

Same here John. I lived in downtown Pennington gap then at an Elevation of just 1360 and recorded 52 inches for the Season. Much of the Area received more due to Elevation. Wise set State Seasonal Record with 123.4 inches.

[Carvers Gap]

The 6z GFS might be its coldest run yet.  The 0z Euro and CMC have several light events which are northern stream driven.  Models continue to get colder.

[Carvers Gap]

The GFS has had this time frame(give our take a couple of days from Dec 17th) on-and-off as a potential time for very cold air.  The 0z Euro also has this but just a bit shallower.  The extreme solutions have not verified yet, but only IMHO because climatology really hasn't supported it yet.  By mid-December, very cold air has precedent over the valley regions.   This also fits recent MJO rotations - I have not looked a today's as of this post.

Again, if you like nickel and dime events(sometimes w/ mixed precip), the next 2-3 weeks are full of them.  Let's see if they verify.  Right now the trough axis is slightly too far to the East.  Where is the actual SER when you need it, right?  

[Daniel Boone]

After the shafting we Tennessee Valley Folks got from this one hopefully we get lucky with the other's up the pipeline. I had a light dusting from this one. Blacksburg about 5". Even Danville at about 800ft elevation in South Central VA near the NC Line has 3" and still snowing.

[Carvers Gap]

1 hour ago, Daniel Boone said:

After the shafting we Tennessee Valley Folks got from this one hopefully we get lucky with the other's up the pipeline. I had a light dusting from this one. Blacksburg about 5". Even Danville at about 800ft elevation in South Central VA near the NC Line has 3" and still snowing.

I think the next "system" will be Sunday night.  The 12k NAM has it as does the RGEM.  it is coming in at night.  If the NAM is correct, that could be minor to moderate upslope for the Plateau and maybe the Apps. 

The MJO is a "choose your own adventure" this morning at CPC.  It has yet to loop back around.  But....the GFS and Euro now show it stalling in 8 - and I am still not sure that actually happens!  If it actually stalls in 8 for a long period of time(and it is already halfway across 8), that would leave the door open for very cold temps.  I almost kind of wonder if the CFS has it right.  It trucks across the cold phases, rolls through the COD to 6, and then goes back through the cold phases again.  That looks an awful lot like those CHI graphics Jax recently posted.  Strong 1-2, strong Maritime, continues to dateline.  I do think we have a cold shot coming mid month...we'll see if I am right!  LOL.

[jaxjagman]

Not sure the MJO is really stalling out,its during the next few days the signal is getting nothing but constructive interference from Kelvin.Rossby.CFS has been showing this for several days now

[Carvers Gap]

The 12z Euro is frigid w/ a couple of days of real feels that have below zero readings.  Both the 12z GEFS and GEPS ensembles show cold temps some time between Dec 14-17th.  I suspect we see an anafront(a constant them of mine I know) at some point in that time frame.  I think we could see 1-2 very cold air masses push through the area mid-month.  And honestly, all of us would probably appreciate some moderation if those come to pass.

[Carvers Gap]

The 12z GEFS has temps twenty-five degrees below normal in WI at 195 w/ all of that headed SE.  During that same hour, our forum area has departures of fifteen degrees BN.  That is frigid for an ensemble at this range. The 12z GEPS is even colder over our forum area w/ temps 20 degrees BN over much of the area. The GEPS brings another cold shot around the 21st.  

The 12z EPS is rolling.  It has the same cold shot, and is a bit "warmer."  It is only 10-15 degrees BN.  That is cold for a model w/ a bit of a warm bias in d10-15.

Short story, even at this range, there is a growing likelihood of very cold air making it to our latitude by mid-month.  Both the GEPS and AIFS ensemble(to some extent), show the second cold shot around the 20th.  With so much snowpack immediately to our north, these cold air masses are on greased skids.

[Carvers Gap]

Just looking at northern hemispheres modeling, the coldest air on the planet will likely be over the Yukon d8-15 roughly.  The mechanism to deliver that into the Upper South is present in the forum of a flat western ridge.  The colder of the air (for now) will slide across the upper MidWest and into the NE.  HOWEVER, any kind of cutter or storm which gains latitude could send all of that into the Tenn Valley region.  Both the 6z GFS and 12z Euro have minor slp events which do it.  I cannot imagine what a big storm would wrap in.  A portion of the TPV is basically parked over the Hudson Bay, and just pinwheels cold air southward. In other words, we have a trough modeled.  The source region for that trough is very cold air.  Remember these winters where NA was void of BN air...not this year!

[Carvers Gap]

I mentioned 95-96 yesterday.  Interestingly, the d8-14 analogs have that analog(I didn't see it until today FTR).  I am glad not to see 83-84 in that mix!  Dec 2012 is double weighted as well.

19951129
20161209
20121128
20221129
19961223
20101212
19951204
20211222
20121203
20081231

[jaxjagman]

22 minutes ago, Carvers Gap said:

Just looking at northern hemispheres modeling, the coldest air on the planet will likely be over the Yukon d8-15 roughly.  The mechanism to deliver that into the Upper South is present in the forum of a flat western ridge.  The colder of the air (for now) will slide across the upper MidWest and into the NE.  HOWEVER, any kind of cutter or storm which gains latitude could send all of that into the Tenn Valley region.  Both the 6z GFS and 12z Euro have minor slp events which do it.  I cannot imagine what a big storm would wrap in.  A portion of the TPV is basically parked over the Hudson Bay, and just pinwheels cold air southward. In other words, we have a trough modeled.  The source region for that trough is very cold air.  Remember these winters where NA was void of BN air...not this year!

Strong blocking into the Western Aluetians,Bearing Sea being shown would pump up a +PNA but where does the Trough Axis set up,definite cold look towards the Mid month

[Carvers Gap]

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

[Carvers Gap]

Might have been a hiccup, but the 18z GFS lollipopped NE TN and SW VA for Sunday into Monday....as in half of a foot.

[Carvers Gap]

Best I can tell is that we caught the same jet streak from the 12z run, but it backed flow just a bit.  That is an extreme outlier, but interesting.  Doubt it will be there in the future, but something to keep an eye on w/ low expectations.

[Daniel Boone]

2 hours ago, Carvers Gap said:

I mentioned 95-96 yesterday.  Interestingly, the d8-14 analogs have that analog(I didn't see it until today FTR).  I am glad not to see 83-84 in that mix!  Dec 2012 is double weighted as well.

19951129
20161209
20121128
20221129
19961223
20101212
19951204
20211222
20121203
20081231

There's a Couple of Duds in there('16-17, 22-23) as well as a couple of near Normal One's('96-97, 12-13, 08-09) along with a Couple great Winter's ('95-96, 10-11) '21-22 was a good Winter along the Cumberlands and western locations but not area wide . I bet they just did the last 30 Year's with these.

[Carvers Gap]

1 minute ago, Daniel Boone said:

There's a Couple of Duds in there('16-17, 22-23) as well as a couple of near Normal One's('96-97, 12-13, 08-09) along with a Couple great Winter's ('95-96, 10-11) '21-22 was a good Winter along the Cumberlands and western locations but not area wide . I bet they just did the last 30 Year's with these.

They added 09-10 today.

[Daniel Boone]

Just now, Carvers Gap said:

They added 09-10 today.

One more great one !

[Carvers Gap]

You know, the 12z AIFS had a similar solution to the 18z GFS.  I just didn't look that closely.  It just wasn't as much snow, but still 1-3" of it.

[Carvers Gap]

The 18z GFS apparently popped a weak coastal and backed the flow.  Definitely want to look at ensemble members regarding that.  For a progressive model to form a weak coastal....that might be something to watch.  It would normally be the first OTS.

[Daniel Boone]

3 minutes ago, Carvers Gap said:

You know, the 12z AIFS had a similar solution to the 18z GFS.  I just didn't look that closely.  It just wasn't as much snow, but still 1-3" of it.

Yeah, this one may have Legs for us providing the Jet doesn't shift north any. Incidentally, our first major Snowfall of '95-96 was on the 10th. I measured 7" in Pennington gap. 

[Carvers Gap]

10 minutes ago, Daniel Boone said:

Yeah, this one may have Legs for us providing the Jet doesn't shift north any. Incidentally, our first major Snowfall of '95-96 was on the 10th. I measured 7" in Pennington gap. 

The 18z ICON hints at it w/ a second wave of precip.  I would be really surprised to see it deepen this close to the event, but the dynamics are there.  Just a timing thing I guess.  All I can see as a difference is a weak area of lp forming along the coast.  I am not sure if a lee side forms or an inverted trough forms.  I am terrible at seeing inverted troughs.  

[Carvers Gap]

I really thought there would be zero support for the 18z GFS solution w/ ensemble members, but there are a decent number which have similarity. There were almost none of those at 12z.

[Carvers Gap]

This is probably a more favorable trend for our folks in North Carolina, but you can see the various iterations of precip backing.

[Carvers Gap]

I kind of see this more as a system where NE TN folks(SW VA) see the snow hang on just a hair longer w/ NW flow to follow.  It isn't a big NW flow event, but it is present on all short range models, especially for the Plateau.

[Daniel Boone]

I do wish we had a bit more cold in Place. If a Lee side develops that won't be a problem. In 95-96 we had snow producing waves akin to last night but with well established Cold in place. We had several Miller B to Miller A Transfer's . Couple of those were big Dogs that went on to be powerful Noreasters. There were a couple decent Clippers as well. 

    I will say, imo we're on track to have a great Winter Snow wise . The Cuban heat HP that had the deep SE flooded with very warm Temps and aided the mild upper Layers of our area to be as mild as they have has weakened and shifted SE. 

[Carvers Gap]

1 minute ago, Daniel Boone said:

I do wish we had a bit more cold in Place. If a Lee side develops that won't be a problem. In 95-96 we had snow producing waves akin to last night but with well established Cold in place. We had several Miller B to Miller A Transfer's . Couple of those were big Dogs that went on to be powerful Noreasters. There were a couple decent Clippers as well. 

    I will say, imo we're on track to have a great Winter Snow wise . The Cuban heat HP that had the deep SE flooded with very warm Temps and aided the mild upper Layers of our area to be as mild as they have has weakened and shifted SE. 

Agree.  As noted by a poster in another forum(maybe ENSO on the main page), this is a pattern which is often hard to break down, i.e. cold over the Hudson Bay, a small ridge over the Southwest, and kind of a flat, stable trough in the East.  That Alaska feed into the SE is a classic old-school pattern.  I know we've talked about it before.  It seems like modeling has shown this in the past only for it not to verify.  This time it is in place.  That is a cold, cold feed at times.