December 2025 Short/Medium Range Forecast Thread

[Daniel Boone]

1 hour ago, GaWx said:

Look at how much the EPS has cooled for the lows of Dec 30th in just 6 runs thanks to the pushback from the strengthening -NAO despite the Aleutian ridge not budging!
It has cooled this much from the Friday 12Z run, an amazing amount for an ensemble mean over such a short period:

- Roxboro, NC 12F from 38 to 26
- Charlotte 14F from 40 to 26
- CAE 14F from 43 to 29
- SAV 15F from 48 to 33
- ATL 18F from 45 to 27
- Chattanooga 19F from 41 to 22
- Nashville 19F from 42 to 23
- Birmingham 20F from 47 to 27
- Tupelo 19F from 48 to 29
- Chicago 13F from 30 to 17
- Tulsa 11F from 43 to 32

12Z 12/19 EPS:

0Z 12/22 EPS:

You have the maps listed opposite Larry. The bottom is 19th.

[Daniel Boone]

4 hours ago, Holston_River_Rambler said:

I know it’s all fantasy but I think the 6z GFS was about to give us a new years present if it had run about an extra 36 hours. 

 

 

That Block will either cause that northern plains/ Southern prairies LP to weaken and drift SE or shift South.

[tnweathernut]

1 hour ago, Matthew70 said:

Congratulations!  Enjoy because they grow fast.  My two kiddos are  now 22 (boy)19 (girl).  

Right there with you, except 22 (girl), 19 (boy).....  And yes, blink of an eye.  Crazy fast.

[tnweathernut]

13 hours ago, Matthew70 said:

This forum is the best of any of them.  Everyone gives sound reasoning & terrific discussion as to why.  Everyone is welcoming & helps others learn. There is no negativity & winter cancel thankfully.  Yeah the pattern has not been the best for snow in TN but when has there ever been a snowy December in TN? Yet many places have had a lot of snow already.  As Carver said it’s been a well below average December.  Many days have been like a January day.  December has been a win in my book.  It’s felt like Christmas! I do hope everyone is having a great Christmas season & wish everyone a Merry Christmas! 

Even when I'm negative on here, I'm still optimistic at heart.  It's common for a snow lover to be that way.   When it comes to snow in the south you'd be silly to cancel winter in December.  We usually only hope for a widespread threat or two all year and it seems flukey snows happen as much as well modeled ones.  Might as well hold out hope through early spring.   

I think one of my only contributions lately has been noting the stubbornness of the ridge in the Aleutians not being good for business (snow and cold).  I was surprised to see @Carvers Gapmention 1996 had that feature. 

[Carvers Gap]

The 12z Euro is about to send it late in that run....

[Carvers Gap]

Here is what is interesting.  The Euro doesn't see cold...until it does.  When it finally gets it in its crosshairs, we usually are good.  

So, on to the 12z Euro....There is a cold front on the 28th which is getting colder with each run - thanks to @GaWx for the ensemble info.  The Music City Bowl...moderation of temps would be appreciated(Dear CMC).  I about froze at the Vandy game w/ a stiff little 5-10mph wind in my face in the South end zone.  In my younger days, no problem.  Back to the point...the Euro has another cold front on the 2nd which looks legit cold.

General takeaways....IF the NAO is in place and has staying power, it very well could pinwheel one cold shot after another w/ warm interludes.  It would force that cold well south per @Daniel Boone's comments - I agree.  

Those were some WILD runs at 12z.  Want some fun?  Go look at the 500 map for the CMC at 240.  Then, go look at the surface pressure anomalies under that.  Then, go look at temp departures from the norm.  Single digits sitting under a monster 500 ridge.

How does it doe that?  Welcome to the NAO.  Basically, the cold air gets sent into the SE, and it can't escape out to see due to the Atlantic block.  It gets trapped.  I have no idea if that is right...just so counter to what we normally look at.  BUT, if that is really, that is an ice storm setup if I have ever seen one.  Like I said...crazy 12z runs.

The interesting question.  Is modeling still playing catchup?

[Carvers Gap]

The 12z AIGFS(no idea how accurate that model is???) also sends a pretty strong cold shot around Jan 2-3.  It is more Texas centered, but spreads eastward.  It has an anafront - there is that word again.  Models were overly strong w/ the early December cold.  We have to guard against that, but this is January.  Climatology favors colder air masses.

[Carvers Gap]

Just for kicks and giggles...12z AIGFS gives us this look.  That will certainly change, and was a red herring in early December.  However, IF the second cold shot is real, I would certainly think winter wx might be on the table.  At some point, one of those warm air masses with lots of humidity won't get out of the way fast enough.

[Holston_River_Rambler]

It's not a winter if we don't have at least one anafront where the cold doesn't make it across the plateau quickly enough for East TN Valley. 

[Carvers Gap]

The gradient boundary presses further and further southward with each passing surface wave.  If we can line up precip on an east-west boundary, we could see a slider in play.

[Carvers Gap]

Take a look at the difference in on the ensemble between 18z GEFS yesterday and 12z today...I have been griping about this for weeks.  This is for Dec 28-29.

There were a few really strong warm air masses embedded in the ensemble mean.  They were greatly skewing the mean - even though there were a greater number of colder members included.  As we get closer to the event, the anomalously warm air masses are subtracted.  And we get this substantial move.  

Do I still think we see chinooks?  Yes, that seems baked in the cake.  However, this may we a winter where the colder air masses get colder as reality gets closer.  Those are kind of fun winters BTW.  We don't get a lot of those.  Normally, we see cold air masses moderate as they get closer to reality - Ex A is early December.  

To be clear, I do want to see a few more runs before declaring the Jan 2-3 cold air mass has legs.  If models are flipping this much, they could easily flip right back.

 

[Carvers Gap]

I know this is a bunch of posts and my apologies.  The 12z para GDPS goes back-to-back w/ cold fronts beginning w/ the 28-29th.   We could certainly be cold and dry.  That is with precedent.  However, the storm track should be suppressed with this.  With the return flow behind these fronts, one would think at some point either the cold air doesn't get out of the way(over running WAA) or the warm air doesn't get out of the way.  To me, the para GDPS is a logical path forward, but by no means not the only one.

[Carvers Gap]

Digging through ensemble members.  It looks like there is potential for another strong cold front on Jan6-7 - per GEFS.  This looks like a very active pattern coming up in regards to cold.  Let's hope some precip can work its way in.  I would think clippers and NW flow would be on the table for even norther portions of Gulf States IF that pattern verifies.

[Matthew70]

NWS is sure on the ball issuing dense fog advisories.  Already one for Christmas Eve.

[Matthew70]

Temperatures for next Monday and Tuesday have definitely went downward the past few days.  A high of 29 here next Monday.  A few days ago it was upper 40s. 

[Carvers Gap]

Just tagging on to @Matthew70's post...Here is the Euro Weeklies (ensemble) map from a week ago and compared to todays run for December 30th.  There is a PNA ridge which is likely just temporary.  There is a -NAO whose duration is TBD.  The Rex block relaxes.  This could easily flip back, but that is big change.  

Want to guess what caught the trend?  The Euro control of all things.  The extended version of the deterministic run possibly sniffed out out this cold front at full range(360 hours).

 

[GaWx]

18 minutes ago, Carvers Gap said:

Just tagging on to @Matthew70's post...Here is the Euro Weeklies (ensemble) make from a week ago and compared to todays run for December 30th.  There is a PNA ridge which is likely just temporary.  There is a -NAO whose duration is TBD.  The Rex block relaxes.  This could easily flip back, but that is big change.  

Want to guess what caught the trend?  The Euro control of all things.  The extended version of the deterministic run possibly sniffed out out this cold front at full range(360 hours).

 

This is one of the biggest and most widespread changes toward colder on the EPS mean when going from 2 weeks out to one week out. In reality, most of the colder change has been just since the Friday runs! It’s all because the -NAO got much stronger and pushed back from the NE despite the strong Aleutian ridge remaining!

[Matthew70]

39 minutes ago, GaWx said:

This is one of the biggest and most widespread changes toward colder on the EPS mean when going from 2 weeks out to one week out. In reality, most of the colder change has been just since the Friday runs! It’s all because the -NAO got much stronger and pushed back from the NE despite the strong Aleutian ridge remaining!

I will say you GaWx & Carver have been all over this.  Thank you for sharing!

[Matthew70]

Not weather related but I gotta say.  My job had me in the right spot to get to meet the GOAT (Saban) & shake hands with him.  Merry Christmas to ME!!!!

[Met1985]

23 minutes ago, Matthew70 said:

Not weather related but I gotta say.  My job had me in the right spot to get to meet the GOAT (Saban) & shake hands with him.  Merry Christmas to ME!!!!

That's freaking awesome. 

[Carvers Gap]

So far, we have a brand new baby Flash and a Nick Saban connection in this thread.  The day just keeps getting better.  

The point and click below is pretty wild in my book.  Is the "thunder in the mountains" rule going to score coming out of this?  I am gonna post these here and see how many verify....

My iPhone has my local at 60F on Sunday for a high and then maybe doesn't go above freezing again until Wednesday(not this Weds)!!!

The Native Americans noticed Chinooks first in the Pacific NW according to Wikipedia(I did not know this).  I am nearly certain the Native Americans of the Plains were thankful for it.  In the Plains, chinooks also helped farmers get their cattle through winter.  It also allowed for snow to evaporate and dissipate, thus limiting catastrophic snowmelt during spring.  It has a purpose.  Great article here in this link.

https://sheridanmedia.com/news/185207/history-chinook-winds/

It has been scientifically determined that the Chinook wind, falling from mountain to plain is warmed at the rate of about 1–degree for each 180 feet of descent. A fall of 5500 feet from the summit or the Cascade mountains to the wide plateau of the interior will rise the temperature of the wind by about 80 degrees.