December 2025 Short/Medium Range Forecast Thread

[Carvers Gap]

@Holston_River_Rambler, you jump right in here with your nifty short range graphics.  I don't want to be taking your job!  Here is the RGEM right before the map above.  It dissipates as it heads south.  As we so overnight, sometimes it hold together.  So, let's watch the trend on this.  The 3k NAM is generally just a higher elevation event.  With such a strong air mass coming in, the jet streak with this might help.  Also, a lot of models won't see lower level moisture getting squeezed out w/ below zero air masses.  This might be 15:1 or 20:1 type of stuff.

[Carvers Gap]

I am going to try a new way of posting.  For the 12z suite, I am going to put all note here instead of 5,000 posts in a stream of thought fashion.  I will simply edit and amend this post as the 12z suite progresses.  Feel free to comment!

12z CMC...is having nothing to do with a prolonged warm-up prior to 240.  It has the Dec 20th cold front.  

12z GFS...Doesn't have the 20th cold front, but has one on the 23rd.  The 12z GFS...gasp...erases the furnace by 276.  

JB mentioned that last night that all it will take to dump more cold into the East would be for a piece of that trough to split and head eastward.  That is the 12z GFS.

haha.  The 12z GFS has snow showers along the Virginia apps on Christmas Eve.  What a turn of events.

Feedback.  Have I talked about that?  Well, the deterministic models (GFS and CMC) have less of it over the NW.  That, in turn, reduces the raging chinook which develops with west-east flow.  It really isn't a problem to have a ridge roll through in front of a NW PAC slp.  It is a problem when that slp spins, reforms, spins, reforms, spins....  With that feedback loop lessened, the trough gets kicks eastward and an Alaska ridge pops.

The MJO plots on CPC are much more favorable than the previous days.  That may be why we are seeing more cold fronts on medium and long range modeling.  Will we see a complete reversal of the heat wave back to a cold shot?  Probably not, but just a normal ridge or two rolling through is not a huge problem.

If I was waiting on cold and saw the GFS/CMC begin to eat into it the way they just did the warm spell...I might call that a can kick and question whether it actually comes to pass in large quantities.  

To me, this looks like a back-and-forth pattern w/ a great cold source which comes eastward with any kind of amplification whatsoever.  

Good trends.  I will have a separate post on the Euro if it is similar.

Feedback on the GFS 300+ is pretty apparent off the West Coast.  If that is feedback, the trough roars into the East. ---> almost the exact some thing which led to the head fake(warm up) for earl December.  It pumps the ridge in the East.  Without out, that amplification is less or absent.

When we see a storm exit Washington state, drift southwest with no steering, and it amps up...that doesn't look realistic to me per the GFS.  If that gets worked out, a colder east is possible and even likely.

[*Flash*]

A bit more bleak for west/middle TN these days. Hoping some hope can pop onto the scene during this ROM torchfest.

[Carvers Gap]

5 minutes ago, *Flash* said:

A bit more bleak for west/middle TN these days. Hoping some hope can pop onto the scene during this ROM torchfest.

I think this winter is a second half winter for you all.  Middle and West have far outdone NE TN during the 2020s which is wild...even Knoxville has.  Generally, the cold finds you all at some point during recent La Nina climo.  I think u all will be good.

[Carvers Gap]

The 12z Euro continues the 12z suite trend of muting or erasing entire sections of the warm-up.  More posts to follow here...I will just edit this post.

Run-2-run changes for maybe a not so random day...ensembles don't reflect this yet, but the trend is pretty hard to ignore.  I wouldn't quite call it a flip as plenty of warm persists, but the standing wave - poof.

 

[Carvers Gap]

Essentially the pattern is this at 12z.  A slp slides into the NW(just ignore the runs where it stalls, reforms, slides to the southwest in perpetuity, etc).  When that strong lp slides across the Rockies, the counter-clockwise rotation forces a strong chinook which races eastward.  As the slp slides into the Plains, it drags extremely cold air behind it.  That cold then slides eastward.  Wash, rinse, repeat.  If the SLP stalls over the NW(likely feedback), then it pumps a crazy ridge in the east.  

Ensembles are washing this pattern out.  Now, I fully admit the SER could out-duel the incoming cold.  But the corrections at 12z seem to infer a very back-and-forth pattern which would feature NW flow snow, severe, record warmth, and possible record cold.  Wild West.

And really, it is not a SER which were are fighting...it is a chinook on steroids.

I think when the ridge in the East is anomalous, you will find a feedback issue off the West Coast.  It isn't quite the Baja low feedback issue, but it is in the same part of the world w/ the same result.

[jaxjagman]

12 minutes ago, *Flash* said:

A bit more bleak for west/middle TN these days. Hoping some hope can pop onto the scene during this ROM torchfest.

Like always in a NINA it seems,we see some flakes.If it snows it will be in March where it screws up severe

[Carvers Gap]

3 minutes ago, jaxjagman said:

Like always in a NINA it seems,we see some flakes.If it snows it will be in March where it screws up severe

Maybe I am wrong, I thought you all have had several snowstorms this decade.  We have had very few in NE TN.  I thought I rememberedr tracking several with you all.  Were those storms west of Nashville?  Not trying to be smart...I thought Nashville had some decent snows.  I could be misremembering.

[jaxjagman]

1 minute ago, Carvers Gap said:

Maybe I am wrong, I thought you all have had several snowstorms this decade.  We have had very few in NE TN.  I thought I rememberedr tracking several with you all.  Were those storms west of Nashville?  Not trying to be smart...I thought Nashville had some decent snows.  I could be misremembering.

NINOS,not NINAS.I'm not saying it wont snow but chances are better for you guys than us,it should flip next year

[Carvers Gap]

Same feedback error IMHO as ~ three weeks ago.  Two different models - still trying to figure out why there is so much feedback over the West during the past month.  Here is the Euro at 264.   That mid-continent ridge doesn't get pumped without that area of BN heights which has tracked from Calgary into the Pacific (yes, you read that correctly).  Here are the two timeframes....