December 2025 Short/Medium Range Forecast Thread

[John1122]

I suspect it's going to collapse at some point, but the RAP just gave me 4 inches. Sharp cutoff south of about 15 miles north of 40.

[Carvers Gap]

With the axis of this narrow strip of snow, small upstream changes create HUGE downstream changes.  Think of it like this.  When a hurricane is approaching the coast at an angle, any upstream change drastically changes the landfall location.  This snow axis fluctuates with almost every run.  The current 12z GFS is a good lollipop for TRI.  The 14z HRRR is north of its past run and TRI is blank.  I think time of day is going to be huge.   I think likely that some in the forum area will see a stripe of frozen precip along the northwest boundary of this.  Where?  Your guess is as good as mine.  But a line from Nashville to Abingdon, VA, seems about right.  Anyone 30 miles to the south of that and 150 miles north of that is fair game.

[Carvers Gap]

2 minutes ago, John1122 said:

I suspect it's going to collapse at some point, but the RAP just gave me 4 inches. Sharp cutoff south of about 15 miles north of 40.

FWIW, that axis looks about right w/ TRI maybe being a sloppy mess.  

[Scottie16]

So snow in the tn valley is basically a crapshoot at the moment?
I've been trying to educate myself on what makes this particular area so difficult to forecast, it's really fascinating to me.

What I like to do is look on wunderground at the different weather stations throughout the valley. It usually is a good indicator on where the rain/snow line could setup during nowcasting.


.

[John1122]

The 14z HRRR was very similar to the RAP.

[John1122]

The 15z axis is slightly north but bullseyes the Nashville area.

[John1122]

Huge move for the UKIE, it looks about like the 14z RAP. It has been very dry/warm.

[fountainguy97]

Hrrr had me at 40 at 12... it's 34 currently.

[John1122]

There looks to be some snow moving by to my south right now.

[Daniel Boone]

6 minutes ago, John1122 said:

There looks to be some snow moving by to my south right now.

Yeah, it appears to be developing sooner than Forecasted. Could be Virga for some time due to a dry Layer. However, Cloudcover did fill in quicker than expected so precip may very well as well. KMRX should hoist Advisories shortly . 

[Carvers Gap]

It isn't warm out there.  The current HRRR has 1-2" over TRI w/ snow still falling at the end of the run.  Both the 12z GFS and Euro have light amounts as well w/ the GFS having more. The NAM is pretty meh over TRI.  

***Winter Weather Advisories are posted for northern areas.  MRX has seen the 12z suite.***

[Carvers Gap]

Temps in Kingsport range from 35-39F.   It is a lot colder than I expected it to be.

[Carvers Gap]

Once this stuff starts falling, we need a brave soul to post a thread or the "storm."   It ain't gonna be me.  LOL.  The EB looms....

[Carvers Gap]

URGENT - WINTER WEATHER MESSAGE
National Weather Service Morristown TN
1214 PM EST Thu Dec 4 2025

TNZ012>017-035-036-045>047-050500-
/O.NEW.KMRX.WW.Y.0011.251205T0000Z-251205T1200Z/
Scott TN-Campbell-Claiborne-Hancock-Hawkins-Sullivan-Morgan-
Anderson-Unicoi-Northwest Carter-Southeast Carter-
Including the cities of Howard Quarter, Clinton, Smokey Junction,
Sandlick, Norma, Slick Rock, Sneedville, Caryville, Mooresburg,
Oak Ridge, Big South Fork National, Oneida, Kyles Ford, Bristol
TN, Clairfield, Huntsville, Royal Blue, Springdale, Erwin, White
Oak, Evanston, Treadway, Arthur, Kingsport, Limestone Cove, Lone
Mountain, Elizabethton, High Point, Petros, Harrogate-Shawanee,
Jellico, South Holston Dam, La Follette, Unicoi, Elk Valley,
Fincastle, Pine Orchard, Elgin, and Hampton
1214 PM EST Thu Dec 4 2025

...WINTER WEATHER ADVISORY IN EFFECT FROM 7 PM THIS EVENING TO 7 AM
EST FRIDAY...

* WHAT...Mixed wintry precipitation expected. Total snow
  accumulations of up to one inch, along with a light glaze of ice.

* WHERE...The northern Cumberland plateau and portions of the
  northern Tennessee valley near the Virginia border.

* WHEN...From 7 PM this evening to 7 AM EST Friday.

* IMPACTS...Plan on slippery road conditions. The hazardous
  conditions could impact the Thursday evening and Friday morning
  commutes.

[Carvers Gap]

Just zooming out a bit from this event...there are a lot of potential small events in the pipeline.  The 12z CMC is my "go to" at 12z.  Though the 12z GFS is pretty loaded up with opportunities.

[Daniel Boone]

I see several Mets are apparently ignoring the MJO or not looking at it at all as they're continuing harping that the Pattern will flip to Trough in the West soon. I like Ryan Hall but, he's one for example. He doesn't even give a Reasoning other than bound to. Other's are basing on a Couple of Model Runs or an Alaskan Vortex. 

    I agree the Vortex if gets situated in Alaska will alter the Pattern but not necessarily flip it trough west/ridge east. It could possibly flatten the Flow to weaker eastern Trough. 

    Ryan and the Other's could be suggesting a short lived Flip of which is possible even with the MJO Stage and Greenland Blocking. But why not specify that ? I wonder if their bias is coming through or they're wanting their Winter Outlook to be spot on or just doing the what goes up , must come down. Anyhow, enough rantig on a Subject fitting for later lol. They may turn out right. Back to the main here and now Interest unfolding.

[Kentucky]

JKL issues advisories, I'm still expecting to be rugged.

[Carvers Gap]

37 minutes ago, Daniel Boone said:

I see several Mets are apparently ignoring the MJO or not looking at it at all as they're continuing harping that the Pattern will flip to Trough in the West soon. I like Ryan Hall but, he's one for example. He doesn't even give a Reasoning other than bound to. Other's are basing on a Couple of Model Runs or an Alaskan Vortex. 

    I agree the Vortex if gets situated in Alaska will alter the Pattern but not necessarily flip it trough west/ridge east. It could possibly flatten the Flow to weaker eastern Trough. 

    Ryan and the Other's could be suggesting a short lived Flip of which is possible even with the MJO Stage and Greenland Blocking. But why not specify that ? I wonder if their bias is coming through or they're wanting their Winter Outlook to be spot on or just doing the what goes up , must come down. Anyhow, enough rantig on a Subject fitting for later lol. They may turn out right. Back to the main here and now Interest unfolding.

The Euro, after stumbling and bumbling for 4-5 days(losing the pattern), has a reasonable transition of the MJO.  I think it just keeps rotating around.  The GFS/AmericanModeling has tried to loop it around and been wrong with that on multiple occasions.  Does it stall?  It may.  To me, this looks like it will transit cold phases, go COD 3-5, exit into a strong 6, and come right back around.  The GEPS and EPS looks decent in the long range.  The GEFS keeps pushing back the flip.  I do think we see a ridge(maybe???).  

[Carvers Gap]

What I see from the 12z GEPS and EPS is very cold air in Canada that keeps pinwheeling into the US old school style.  And that setup is a very stable pattern unlike other cold patterns we have seen.  JB noted that wave lengths tend to shorten up during phase 8 and wx models will often struggle with details and strength of cold shots.  If we kind of assumed this pattern began just after Thanksgiving, it makes sense for it to last to Christmas or just after, then Jan is likely warm, followed by another cold shot.  This set-up reminds me a lot of 95-96 in terms of the overall sequence(maybe not the snow).  Last winter did as we'll.

[Coach B]

23 minutes ago, Carvers Gap said:

This set-up reminds me a lot of 95-96 in terms of the overall sequence(maybe not the snow).

It will be interesting to see how it plays out. I've always felt 95-96 was somewhat unique in that whenever it got cold it actually seemed to snow. Jan and Feb that winter were below normal, but only like -2 or -3 here in middle TN. Yet every cold shot seemed to bring snow. On the other hand I've heard the dreaded 13/14 winter brought up by BAM weather in the last couple of days. That winter featured at least 7 different significantly cold shots with barely an inch of snow total in Nashville. January was -7 for the month with only .4 of snow, February was -4 with only .1 of snow. Meanwhile just north of us they were setting yearly snowfall records. That's probably why BAM(based in Indy) would like to see a repeat of that. I think east TN scored a couple of times that winter so some of you may not react as negatively when its mentioned. 

[Daniel Boone]

40 minutes ago, Carvers Gap said:

The Euro, after stumbling and bumbling for 4-5 days(losing the pattern), has a reasonable transition of the MJO.  I think it just keeps rotating around.  The GFS/AmericanModeling has tried to loop it around and been wrong with that on multiple occasions.  Does it stall?  It may.  To me, this looks like it will transit cold phases, go COD 3-5, exit into a strong 6, and come right back around.  The GEPS and EPS looks decent in the long range.  The GEFS keeps pushing back the flip.  I do think we see a ridge(maybe???).  

Yeah, if it goes to high amp 6 most definitely. If you want a cold late December and much of January better hope that doesn't happen as high 6 Pattern will be hard to dislodge if blocking is gone, the PNA negative and the AO Positive particularly if it traverses into the colder phases at low Amp afterward.

[Daniel Boone]

40 minutes ago, Carvers Gap said:

What I see from the 12z GEPS and EPS is very cold air in Canada that keeps pinwheeling into the US old school style.  And that setup is a very stable pattern unlike other cold patterns we have seen.  JB noted that wave lengths tend to shorten up during phase 8 and wx models will often struggle with details and strength of cold shots.  If we kind of assumed this pattern began just after Thanksgiving, it makes sense for it to last to Christmas or just after, then Jan is likely warm, followed by another cold shot.  This set-up reminds me a lot of 95-96 in terms of the overall sequence(maybe not the snow).  Last winter did as we'll.

95-96 would be great as the warmups were short lived. Below average Temps Dec, Jan and February. Blocking was very prominent then.