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?