December 2025 Short/Medium Range Forecast Thread

[Carvers Gap]

4 minutes ago, John1122 said:

The 12z ICON is getting on board for potential snow for the area. Plateau and west on it, with west Tennessee being the jackpot zone.

Is that a some snow on the front end of the system for this upcoming Saturday night as well?

[John1122]

The GFS keeps taking a favorable path but it's too warm for those of us in the East, freezing rain to snow mess for the western areas though.

[John1122]

2 minutes ago, Carvers Gap said:

Is that a some snow on the front end of the system for this upcoming Saturday night as well?

Looks like it's on the borderline for parts of the area. My current forecast is rain and 34.

[Carvers Gap]

This might just be the algorithm for WxBell over-doing this, but interesting....

[Daniel Boone]

35 minutes ago, Carvers Gap said:

This might just be the algorithm for WxBell over-doing this, but interesting....

Yeah, probably low Dp at onset. Hopefully we get a stronger push of cold with the follow-up System the 2nd. As is, a rain to snow in upper Valley at the end. If Models are correct, Northern VA and much of West Virginia are going to get buried. Much of Kentucky looks to get a good amount as well.

[Carvers Gap]

Surprised we haven't had more discussion.  The 12z GFS and CMC look great in the medium and long range - several good windows.  The CMC actually looks good for E TN.  Good 12z run so far.  Euro is inbound currently.

[Carvers Gap]

The 12z Euro is definitely in the CMC camp w/ a flatter wave.  

[Carvers Gap]

The biggest things I am noticing at 12z are the potential for slp to form as cold front drags its feet across the souther Gulf states.  I am also seen very cold air masses that seem to have little difficulty making it to our latitude.  The cold air supply in Canada appears ample.

[Carvers Gap]

Ah, and one last ironic thing which I am noticing(and mentioned yesterday)....I think there is the danger of suppressed systems due to the strength of these air masses.  But the souther stream looks active regardless.  If we can get 1-2 systems to connect with the cold, we would be in business.

[John1122]

The late month could be, if everything works well, very epic, even beyond this next two weeks with several potential events. The Euro has the MJO in the low amp/c.o.d into late December/Early January. @GaWx has noted that essentially every low amp pass through 8 has coincided with well BN temps, but that high amp passes were not always cold in the east. 

East Asia should become more favorable soon, to allow west coast ridging downstream as well.

[Carvers Gap]

We all are guilty of HOT takes.  I will be more than happy for this to happen every time I predict warm weather to occur.  I have had some good ones, but this might be a winner from last Friday.

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.  

Maybe I should have clarified.  A standing ridge over...Cuba.    -> 

[Daniel Boone]

19 minutes ago, Carvers Gap said:

We all are guilty of HOT takes.  I will be more than happy for this to happen every time I predict warm weather to occur.  I have had some good ones, but this might be a winner from last Friday.

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.  

Maybe I should have clarified.  A standing ridge over...Cuba.    -> 

At least you own it brother,lol. Many of us fell for it. The Warmanistas are still trying to twist their reasoning and deny any fails. 

[housemtnTN]

I'm a complete noob at this but I think I can say with confidence it looks like we're in for a interesting next couple of weeks lol!

[jaxjagman]

Believe the GFS and Euro are killing the MJO off to fast  in the WP mainly because of a Kelvin Wave is causing destructive interference.MJO is more than likely still active and moving 

[GaWx]

3 hours ago, John1122 said:

The late month could be, if everything works well, very epic, even beyond this next two weeks with several potential events. The Euro has the MJO in the low amp/c.o.d into late December/Early January. @GaWx has noted that essentially every low amp pass through 8 has coincided with well BN temps, but that high amp passes were not always cold in the east. 

East Asia should become more favorable soon, to allow west coast ridging downstream as well.

Hey John,

 Thanks for bringing up the amp. What you said generally coincides with my thoughts. But I’d like to clarify what I’ve said just to make sure there’s not a misunderstanding. Indeed, various analyses I’ve done over the last 10-11 years or so, which all have involved calculations of actual temperatures in a place or places in the E US, have shown that the average anomalies have tended to be colder with low to moderate amp (1.7 or lower in my latest study, which was 8+ day long phase 8s) vs strong AMO of phase 8. But not “essentially every low amp pass”. It’s more like a majority of low amp have been cold vs pretty balanced for high amp.

[John1122]

3 minutes ago, GaWx said:

Hey John,

 Thanks for bringing up the amp. What you said generally coincides with my thoughts. But I’d like to clarify what I’ve said just to make sure there’s not a misunderstanding. Indeed, various analyses I’ve done over the last 10-11 years or so, which all have involved calculations of actual temperatures in a place or places in the E US, have shown that the average anomalies have tended to be colder with low to moderate amp (1.7 or lower in my latest study, which was 8+ day long phase 8s) vs strong AMO of phase 8. But not “essentially every low amp pass. It’s more like a majority of low amp have been cold vs pretty balanced for high amp.

Thank you for the clarification!

[jaxjagman]

GTH Outlook Discussion

Last Updated - 11/25/25

Valid - 12/03/25 - 12/16/25

Recent observations of tropical convection and the global tropical circulation indicate that the Madden-Julian Oscillation (MJO) remains active, with the enhanced convective phase over the West Pacific. Little eastward propagation was evident on the RMM-based MJO index during the past two weeks, however, fluctuations in amplitude are indicative of interference from other modes of variability. The biggest disruptor to the ongoing MJO evolution is the low-frequency La Niña base state, which is preventing upper-level easterlies, low-level westerlies, and widespread convection from crossing the equatorial central Pacific. Enhanced convection is crossing the central Pacific away from the Equator, however, especially along the South Pacific Convergence Zone (SPCZ) region. Time-longitude analyses of the low-level zonal wind field reveals two distinct features propagating eastward: a slowly evolving envelope of westerly anomalies that has progressed from the Indian Ocean in October to the far western Pacific by mid- to late November, and a faster moving signal, likely Kelvin wave activity, that is circumnavigating the globe. As this latter signal comes into phase with the slower evolving signal, westerly wind bursts have occurred, followed by a period of increasing disorganization. Dynamical model forecasts are in good agreement that a period of constructive interference between these two signals will occur in late November and early December, resulting in a disruption of the La Niña trade wind regime over the west-central Pacific, and a rapid amplification of the RMM-based MJO index in Phase-7. Beyond this period, the faster moving mode becomes more unpredictable and may not well capture an easterly phase of the Kelvin wave, but the slower-evolving low-level westerlies are favored to continue impacting the Pacific basin into mid-December. A potential second enhancement of the MJO signal is clearly depicted in both the GEFS and ECMWF model systems during late December over the East Pacific, likely tied to another period of constructive interference between the slowly propagating signal and the Kelvin wave activity. Based on this guidance, the MJO is favored to remain active, and may become the dominant contributor to the global tropical convective pattern during early December. Pacific MJO events teleconnect well with the midlatitude circulation during the Boreal winter season, and may contribute to a reinforcement of ridging across western North America and troughing over eastern North America.   https://www.cpc.ncep.noaa.gov/products/precip/CWlink/ghaz/index.php

[John1122]

Shaping up to be another GFS vs Euro battle. The GFS remains amped, the Euro remains mostly ots/suppressed.