December 2025 Short/Medium Range Forecast Thread

[Carvers Gap]

Well, the 12Z Euro beat me to it...LOL.  That is quite the correction.  Is it done flipping and flopping?  I doubt it.

[Carvers Gap]

The 12z Euro (it hasn't run on WeatherBell...but has on pIvotal) gets rid of the infinite feedback loop and kicks a strong trough into the East and completely flips the d10-15 pattern.  Is it right?  No idea.  But I feel like I have seen this movie before....like about 2-3 weeks ago.  

[John1122]

5 minutes ago, Carvers Gap said:

Is that a different RMM1/RMM2 than CPC uses?  I noticed it is ABM generated.  I haven't seen the CPC site go into 6, and it is updated to the 11th.  Here is the CPC site's for today.  It never crosses into 6.  If they are different, I wonder which is more accurate.

Now, back to model feedback, and the 12z GFS was EXTREME with it today.  I figured that if was noticing at 500, the surface had to be crazy.  This is a comparison of the AIFS and GFS at 12z.  Notice anything?  This is how we know that we are dealing with model feedback, OR the ski slopes in the Sierra Nevada are about to get buried(not without precedent BTW).

 

 

From what I understand, the ABM one there is the actual verified MJO plot, and that there's a 3 day lag time for it per Gawx. I believe the GFS there is likely a model estimate. 

[Carvers Gap]

The 12z Euro slides a 1052 hp into the Plains late in its run.  Wild swing.  I will post some graphics when my stuff updates.

[Carvers Gap]

1 minute ago, John1122 said:

From what I understand, the ABM one there is the actual verified MJO plot, and that there's a 3 day lag time for it per Gawx. I believe the GFS there is likely a model estimate. 

I "think" the black line is the observed index.  The black line is the same on the Euro.  The starting points for the model are the 11th.  Prior to that I "think" is observed.  It is possible the CPC site corrects that later?  I haven't really watched to see if they change it, but I don't think they do.

[John1122]

1 minute ago, Carvers Gap said:

I "think" the black line is the observed index.  The black line is the same on the Euro.  The starting points for the model are the 11th.  Prior to that I "think" is observed.  It is possible the CPC site corrects that later?  I haven't really watched to see if they change it, but I don't think they do.

This was his quote about it. I could be wrong as you two know much more about it than me.

 

Quote

There’s been an ~3 day lag time in getting the official MJO phase/amp. As it turns out, the initial phase 8 lasted only 5 days (12/3-7) as it went into phase 6 on 12/8 (per 1st image), which was totally unexpected. I’ll keep following this closely to see if it re-enters phase 8, which I think has a very good chance but we’ll see.

 

[Matthew70]

4 minutes ago, Carvers Gap said:

The 12z Euro slides a 1052 hp into the Plains late in its run.  Wild swing.  I will post some graphics when my stuff updates.

And that phrase that we’ve heard on college game day not so fast, my friend.  

[Carvers Gap]

4 minutes ago, John1122 said:

This was his quote about it. I could be wrong as you two know much more about it than me.

 

 

I will be interested to see if CPC updates their official plot.  I honestly don't know if they derive their own plot or get it from ABM.  I haven't ever thought about it.  Thank you for clarification on that.

[Holston_River_Rambler]

12z RGEM pops a little band of moderate snow as far south as Morristown around sunrise tomorrow. 

[Jed33]

I’ve noticed the rgem was teasing my area a lot the last few runs. The euro to some degree as well

[Carvers Gap]

5 minutes ago, Matthew70 said:

And that phrase that we’ve heard on college game day not so fast, my friend.  

We saw this EXACT thing happen already in this short winter.  I referenced my erroneous Nov 21st post yesterday(which caused some confusion).  Let's see if the Euro stays with that solution.  But the 12z Euro is a great example of what happens when things don't stall or feedback over the Pac NW.  I have little doubt the GFS is having trouble in that region, but I don't remember it having feedback issues w/ troughs there.  It does have some issues with building up cold air masses in the Canadian Rockies front range and then not kicking it out.  But w/ the comparison I had above w/ the snowfall amounts vs AIFS, the GFS is an outlier at this time.  Now, it can snow out there big time, but it really is out on a limb.  When the trough doesn't stall there, it "should" kick out which it did on the Euro.

The bad thing about that possible error is that it absolutely wrecks LR ext (weeklies) until it gets fixed.  

And if we are looking at 1055 HPs coming out of Canada, that would explain the models bouncing around.  

[Holston_River_Rambler]

2 minutes ago, Jed33 said:

I’ve noticed the rgem was teasing my area a lot the last few runs. The euro to some degree as well

If you take the 15z RAP verbatim,, I call 1-2" tomorrow for Kingsport, Bristol, and JC. Heading to Boone in the AM, so hopefully I get in on the action too! 

[Carvers Gap]

1 minute ago, Holston_River_Rambler said:

If you take the 15z RAP verbatim,, I call 1-2" tomorrow for Kingsport, Bristol, and JC. Heading to Boone in the AM, so hopefully I get in on the action too! 

Bring me some snow, Holston.

[Holston_River_Rambler]

Just now, Carvers Gap said:

Bring me some snow, Holston.

I'm halfway ready to pop an obs. thread for tomorrow. I'll play it safe and wait until around 7PM and see how things look. 

[Holston_River_Rambler]

I mean, this is the sacred and rare clipper, seem like it's been since the early 2000s that I remember a no muss no fuss clipper. 

[Holston_River_Rambler]

That is a very unusual water vapor image IMO:

 

[Holston_River_Rambler]

I couldn't tell you why I think that's unusual, except in looking at these sorts of images over the past few years, that looks odd. 

[John1122]

The 18z HRRR tries to bring the clipper in a little further west initially with a band of snow from Scott Co Tn, through to about Maynardville and points east.

[Holston_River_Rambler]

Biggest caveat I can see now for this clipper, would be the inevitable 2 hours of virga on the front end

[Carvers Gap]

Not clipper, but interesting I think...The 12z Euro loses the infinite loop feedback over Pac NW.  We saw something similar w/ the repetitive and erroneous Baja lows earlier this month.  The 12z GFS got locked into a Pac low(maybe it is right?) complex, but the Euro kicked the trough eastward.  Take a look at the differences.  There is cold air drainage into the NA Prairies on the Euro.  Compare that to the GFS at the same hour.  Now to be fair, the GFS eventually kicks everything eastward.   I think anytime we see a standing ridge over the SE this winter, we are really going to have to question what is going on upstream.  Those ridges can happen and there is precedence.  But they have been mirages this winter.  I do think a Chinook is coming.  But until the PAC NW repetitive low situation gets resolved, everything after that is probably a crap shoot.

BTW, infinite loops have always interested me, mainly because they are a pain to programmers.  I had to take three programing classes at UT.  Infinite loops were challenging puzzles to solve, and sometimes a huge pain in the you know what.  

We really want to be routing for that 1050+ hp to continue to show up on modeling.  This could be a blip, but worth watching.  

 

[jaxjagman]

Euro the last couple runs has been showing signs of the Subtropical ridge moving out west,maybe its seeing something  the other models arent seeing right now,dunno.But right now it dont seem to have much if any support

[Carvers Gap]

50 minutes ago, jaxjagman said:

Euro the last couple runs has been showing signs of the Subtropical ridge moving out west,maybe its seeing something  the other models arent seeing right now,dunno.But right now it dont seem to have much if any support

I think it is a really amplified pattern.  That is Arctic air under that ridge...1054 hp sliding down the Plains.  Deceptive look for sure.  Cold air is traveling close to the surface...some of the coldest air of the season under that ridge.

[Carvers Gap]

Somewhere, Larry Cosgrove has to be smiling. The Euro Weeklies have a strong EPO by about Jan 17th.  

So, we need to weather the storm between Dec 20 and Jan 20.  It seems like the patterns this winter are not as stable as past winters, i.e. they are shorter in duration(4 weeks and not 6 weeks).  

If we can swing a cold air mass or two during that "warm" time frame, that would be awesome.  If we can find a way to go cold during that time frame, we have a shot at a cold winter.  We are all pulling for the 12z Euro to be a trend and not a blip.  It does actually have support from the 12z GFS which is just about 48 hours later w/ the trough pushing east.  But huge grains of salt at that range.

[Carvers Gap]

Here is a prime example of the ensemble mean being skewed by anomalous members.   I mentioned this yesterday.   A substantial number of members from the EPS(2 sets of panels) and the GEFS (1 panel), have a cold front coming through on Christmas or the day after.  The first group of thumbnails is from the GEFS at 366.  Most of those members have a cold front pushing through.  The EPS also has several members which produce cold.  Surprisingly, the 12z GEFS has more of colder solutions.  (I am pretty sure the GFS and GEFS were not updated at the same time.  That leads to some discontinuity between the two at times.)  This "could" be the first chink in the armor of the duration of the presumed, longer-duration warmup.  Time will tell.  In early December, the first signs that modeling was reverting...the oddball deterministic run which became more common and individual ensemble members.  

 

[Carvers Gap]

The 12z CFSv2 also lends some support to the "jail break" cold pattern potential just after Christmas.

[John1122]

The RAP is giving an aggressive bit of snow shower activity overnight, but it suckered me once a few weeks ago. Thermal issues that time though.

[John1122]

 

[Carvers Gap]

What is the timing onset for TRI(if it gets here) tonight?  I haven't even bothered to look!