December 2025 Short/Medium Range Forecast Thread

[Holston_River_Rambler]

Just now, Golf757075 said:

Do you think it will?

The mountain torquers seem rather excited. Got to have a big old HP slam down from Siberia into east Asia. Of course we have to hope some hitherto little known index does not screw it up. 
 

 

[Golf757075]

1 minute ago, Holston_River_Rambler said:

The mountain torquers seem rather excited. Got to have a big old HP slam down from Siberia into east Asia. Of course we have to hope some hitherto little known index does not screw it up. 
 

 

Would be nice to get a few weeks sustainable cold pattern and take our chances

[Matthew70]

47 minutes ago, Carvers Gap said:

I have been wanting to post that GEM map all day.  We were doing Christmas with some of my family...I definitely was sneaking a peak at models.  But my 12z model deep dive...just now happening.  

There is an interesting demarcation point after the 5th...does it warm up and we get a heavy rain event as Holston posted?  Or does end up frozen(not at those levels)???  I tend to think the cold hangs around, but that is an educated guess and by no means fact.

I’m sneaking looks hoping I see the HOT sign on!!!

[Golf757075]

1 minute ago, Matthew70 said:

I’m sneaking looks hoping I see the HOT sign on!!!

CMC has always been a cold biased model. Sometimes it's right, especially with freezing rain and ice

[*Flash*]

Seeing the 12z EPS/GEFS agree on week 2 cold and a +PNA emerge on modeling today felt like a Christmas present from Mother Nature. How quickly things can change in our field of interest. 

[Carvers Gap]

54 minutes ago, Holston_River_Rambler said:

The mountain torquers seem rather excited. Got to have a big old HP slam down from Siberia into east Asia. Of course we have to hope some hitherto little known index does not screw it up. 
 

 

LOL.  That is a great line.  I always forget about mountain torque events in Asia.  I am assuming this is good or us?

[*Flash*]

58 minutes ago, Holston_River_Rambler said:

The mountain torquers seem rather excited. Got to have a big old HP slam down from Siberia into east Asia. Of course, we have to hope some hitherto little-known index does not screw it up. 
 

 

Why do I feel dirty reading this? Probably just the mountain. 

[Holston_River_Rambler]

25 minutes ago, Carvers Gap said:

 I am assuming this is good or us?

The idea seems to be a jet extension caused by a +east Asian mountain torque will help dislodge the Aleutian high. 

Here it is on the 18z GFS:

Big high drops down into east Asia:

 

Momentum gets added to the pac jet:

 

Aleutian high dies:

20 minutes ago, *Flash* said:

Why do I feel dirty reading this? Probably just the mountain. 

I almost wrote the "mountain twerkers" lol. 

 

Hope that jet extension doesn't go too far. That's burned us in the past. 

[John1122]

Mammoth got over a foot of snow in a couple of hours overnight. Up to 100 inches expected in the area. I like to watch it, but when they're getting buried, we usually are waiting on the pattern to change. 

[John1122]

Mammoth has gotten 28 inches as of 4pm local time.  The forecast through Friday. 

"Tonight

Snow. Steady temperature around 20. Wind chill values as low as -1. Windy, with a south southwest wind 30 to 35 mph, with gusts as high as 55 mph. Chance of precipitation is 100%. Total nighttime snow accumulation of 26 to 32 inches possible.

Christmas Day

Snow. High near 20. Wind chill values as low as -3. Windy, with a south southwest wind around 30 mph, with gusts as high as 60 mph. Chance of precipitation is 100%. New snow accumulation of 33 to 39 inches possible.

Thursday Night

Snow showers. The snow could be heavy at times. Some thunder is also possible. Steady temperature around 20. Wind chill values as low as -1. Windy, with a south southwest wind around 35 mph, with gusts as high as 60 mph. Chance of precipitation is 100%. New snow accumulation of 23 to 29 inches possible.

Friday

Snow showers before 1pm, then snow, mainly after 1pm. The snow could be heavy at times. Some thunder is also possible. High near 18. Wind chill values as low as -4. Windy, with a southwest wind 25 to 30 mph decreasing to 20 to 25 mph in the afternoon. Winds could gust as high as 55 mph. Chance of precipitation is 100%. New snow accumulation of 9 to 13 inches possible."

[John1122]

The Canadian keeps the subzero cold. The GFS lays down some anafrontal snow on Monday now with that cold front passage. 

[John1122]

The GFS is mostly ugly with a capital UGH in the long range. +NAO/-PNA/Aleutian Ridge rock solid. Who knows if it verifies, as it's been flopping back and forth so much lately. 

[Carvers Gap]

The GFS IMHO continues to be a bit of an outlier as it forms and breaks down the NAO rapidly.  I can’t find another model doing that.   I can’t remember which model handles the NAO better. Who know? It might be right. 
 

The GEM is another adamant outlier outlier with its solution.  I would guess it continues to trend towards a NE cold shot vs Deep South. But it has a good habit of finding cold fronts, albeit too intense with its solutions. 
 

The Euro looks like good middle ground - for now.   I would not be surprised to see models trend colder after a warming trend over night.  We have entered that 5-7 day window where things get lost. Also, it would not be surprising if models were simply too quick with the cold.  I am noticing a trend to send the cold on Jan 5 instead of 2nd….even the 8th.  Models are bouncing between those dates. 
 

Remember in late November that modeling had the cold, lost it, and then brought it back. I would not be surprised if we see something similar now.  Been kind of a weird year with model biases and feedback.

With the exception of the GFS, other modeling has the NAO.  So, a great sign that it is still present.  I think it is the Euro which eliminates the Aleutian high late in its run. 

Either way, Merry Christmas to all of you!  Have a great day!!!

[Carvers Gap]

As for Mammoth...their webcams are awesome.  I dropped a link for their cams on the mountain.  Just another world for snow rates.  The cams range from 8000' to 11000'.  

We stayed at 9000' this past summer when we were out there.  It is crazy to see everything buried now.  The ground was bare two days ago - they had almost no snow below 9500'.  Very late season for them.  (Some Colorado resorts further east still have bare ground.)  If they didn't get this storm, I am not sure when they get another window like this.

But...it is easy to see how the Donner party got caught.  People were hiking up until two days ago in the 10,000' range...today, you would be stuck.  I mean the ground in the Sierra Nevada was bare.  They have been super warm while the East has been cold.  

The 6z AIGEFS lent a bit of support to the 0z GEM - it doubled its colder members since 0z.  We probably are going to have to look at ensemble members in order to sort the cold fronts out for early January.  The mean will continue to be skewed until the last minute I think.

 

https://www.mammothmountain.com/on-the-mountain/mammoth-webcam/woolly-cam

[Carvers Gap]

The 12z ICON has moved to the 0z GEM at 500.  Let's see if the 12z GEM actually holds to the 0z GEM!

[Carvers Gap]

12z trends are towards the GEM…to be clear not to that extreme, but a cold eastern US.

[Carvers Gap]

I mean the Jan 2 trends are pretty stark.  Models don’t have the below zero axis of the cold air mass on the GEM, but they have completely erased positive temp anomalies at that time and shifted SW with the cold towards the Ohio and Tennessee Valley regions.

[Carvers Gap]

The trend of models being blind to cold fronts (until a week out) appears to be continuing.   Just so very odd.  

[John1122]

We are creeping towards a possible -NAO/+PNA pattern. It still may not snow, because you just never know here, but that's as good as it gets for the chance of a winter storm here as far as blocking goes.

[jaxjagman]

Basically in winter time when you see rising heights into Mongolia and troughs into East China trough Japan, it should look like this days after or around 8 days give or take

When you see the opposite it should in general be the opposite.

While the NAO also plays a big part in winter time  for us,you'd still want to see a -WNAO and not a -ENAO, a -ENAO  the trough axis moves further east more towards the east coast,you'd prefer a -WNAO,especially for us west of the Cunberland

[jaxjagman]

Merry Christmas to all by the way!!

 

I left one out the more important one,while yes it's a -NAO,its still a more based -ENAO

[Carvers Gap]

For really the first time in a few weeks, ensembles are pretty bullish with the exception of the GFS/GEFS which are just worlds apart from any other model - even its own AI model.  They are outliers.  In my book, though, the deterministic models have led the way.

Something is not right w/ wx modeling right now.  I maybe can remember one winter where modeling was completely blind to cold fronts.  The GEM, with its cold bias, is useful right now, because it exaggerates the pattern enough to find them.  Sometimes when graphics are exaggerated (like increasing exposure on a camera), one can spot details which can't be spotted otherwise.  In this case, the GEM is spotting cold fronts in a similar manner.  Just subtract the cold bias.

My guess is the mistakes are occurring with the MJO region which has no real clear signal, the extreme cold in Canada, the NAO stepping onto the scene, and was the Aleutian high over estimated in terms of staying power?  Throw in some atmospheric river stuff...and it is understandable that struggles are occurring.  But this deal where the GFS can't even see a cold front past d7 is really weird - something has been tweaked in the model IMHO.  It is just missing wildly right now...unless the pattern is warm.

[jaxjagman]

9 minutes ago, Carvers Gap said:

For really the first time in a few weeks, ensembles are pretty bullish with the exception of the GFS/GEFS which are just worlds apart from any other model - even its own AI model.  They are outliers.  In my book, though, the deterministic models have led the way.

Something is not right w/ wx modeling right now.  I maybe can remember one winter where modeling was completely blind to cold fronts.  The GEM, with its cold bias, is useful right now, because it exaggerates the pattern enough to find them.  Sometimes when graphics are exaggerated (like increasing exposure on a camera), one can spot details which can't be spotted otherwise.  In this case, the GEM is spotting cold fronts in a similar manner.  Just subtract the cold bias.

My guess is the mistakes are occurring with the MJO region which has no real clear signal, the extreme cold in Canada, the NAO stepping onto the scene, and was the Aleutian high over estimated in terms of staying power?  Throw in some atmospheric river stuff...and it is understandable that struggles are occurring.  But this deal where the GFS can't even see a cold front past d7 is really weird - something has been tweaked in the model IMHO.  It is just missing wildly right now...unless the pattern is warm.

And it should be a pattern change upcoming unlike we are seeing now,look at East Asia after D3

[John1122]

Merry Christmas to all as well. I started a January thread, as we are now looking into there for the changes.