December 2025 Short/Medium Range Forecast Thread

[John1122]

We are now into December with the OP runs. The first 7 to 10 days of December are likely to be warm, with a possible brief cold shot or two.  After that, we have some potential factors that would introduce cold into the pattern. A cooperative MJO, a well place EPO ridge, a weaker than normal, if not split, SPV, all look possible as we head into the period of December 15thish towards the end of the month. 

 

See Carvers Weeklies post in the fall thread for what December looks like when the Euro has the MJO moving through more favorable areas.  

[Carvers Gap]

D8-14 analogs from CPC today.  Really pulling for the Dec 09 thread to be THE analog.

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[Daniel Boone]

2 hours ago, Carvers Gap said:

D8-14 analogs from CPC today.  Really pulling for the Dec 09 thread to be THE analog.

19851121
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Couple duds in there. '72-73 and 08-09.

2005-06 slightly above Temperatures with slightly below average Snowfall. Very Mild January.. 85-86 was great. below average Temps, above average Snowfall. 64-65 was average with above Snowfall. 96-97 avg Temps and Slightly below Snowfall. 08-09 slightly above Temperatures, below average Snowfall. 80-81 below Average Temps, above Snowfall. 09-10 great. Below average Temps above average Snowfall.

   John, you probably have more detailed information in these.

[nrgjeff]

Glad 2005-06 came up. December got nutty cold. Snow blanketed much of the country. Then it got warm. December cold broke around Christmas in KCMO, which was a little disappointing. January thaw was torch. 

For this year, operational models are of course all over the place. Thanksgiving weekend cold front CF may actually be faster on Thanksgiving rather than the weekend. Then a few milder days are forecast before the next CF.

Weekly products the CFS gets cold established for the first week of Dec, fading during the second week of Dec. The ECMWF weekly doesn't seem to acknowledge the Thanksgiving weekend CF but starts the cold west to east trek the first weekend of Dec. 

Putting it all together, I think the first 1-2 fronts could be brief cold intrusions. Thanksgiving weekend and then middle of the first week or weekend of December. ECMWF weekly struggles to discern the fronts that week. CFS may lock in cold a week early. Perhaps after a couple fronts chip away at the warm pattern, by December 10 give or take a couple weeks can average truly below normal temps. See if we could get that through Christmas for a third week.

Siberia continues to set the table.. for after we work through the North America warm week to 10 days.

Temperature anomalies, blue is cold

Sfc Press anomalies, red is higher

 

[Carvers Gap]

6z Euro AIFS FTW....been wanting to post that all morning.  Cloudfare had other plans.  Thankfully, systems are slowly coming back online.

[Carvers Gap]

Well, well, well...look what the 12z GFS just drug in.

[Carvers Gap]

The 6z Euro AIFS has some company.

[Carvers Gap]

The 12z Canadian has similar set up in terms of cold.  I would not be surprised to see an anafront system develop if the cold is that strong.  The AIFS is 3-4 days later.  Modeling is picking up on a strong cold front...timing TBD.  The Tenn-Vandy game would be pretty frigid if the 12z GFS/CMC were to be correct.

[Carvers Gap]

Ok, you all made me break down and look at the MJO.  I really hate looking at that metric.  LOL.

Well, on pretty much every model it crawls into 7(sometimes 8), loops, dawdles, and stalls.  7 is cold when centered on NDJ.  8 is colder.  It certainly looks like, as John and Boone and others have noted, that LR ext modeling is being driven quite early by the MJO.  That probably is a good thing considering the MJO is in prime real estate by the end of the month.  When it actually arrives into 7-8 is open for discussion.  Nearly every model gets there w/ the BOMM and EMON being optimal.  It just doesn't want to leave the left side of the MJO plot.  

[Carvers Gap]

Some fun stuff.  2009 has been showing up on the CPC analogs for a few days now.  So, I thought I would look at the Euro Weeklies and the 2009 500 map.  I centered the Euro Weeklies map on d10-40.  If I go five more days, the BN mean shifts eastward more.  Some differences, but a decent fit overall.  We know what happened after Dec 2009.  I threw in the GEFS MJO for good measure.

 

[Carvers Gap]

12z CMC ensemble when compared to the surface temp map of Dec 2009.

 

[Carvers Gap]

I don't really do hype.  I know the winter weight which Dec 2009 carries.  The CPC has been using it to balance out their analog package for a few days.  I doubt the entire winter matches this analog, but December(at least the first 2-3 weeks of it) looks like a decent match when compared to ensembles and some LR ext modeling.  Kind of uncanny.  Two different models with similar outcomes in regards to analog matches.  In all reality, those are just MJO matches vs actual analog month matches.  That said, pretty sure the QBO was dropping or negative during Dec 09-10.

[John1122]

If the MJO enters 8 at that amplitude it should be there for a while, and should crawl on through the left side into January.

[Carvers Gap]

It will change, but the 6z GFS shows the potential for the pattern with a slider late in the run.

[Carvers Gap]

MJO stuff...First off, that is not a warm look for December.  In fact, it kind of just crawls through the left side of the plot which is not something we have seen in recent years.  It seems like the MJO almost defaulted to 4, 5, and 6.  How many times have we seen the MJO hit the wall in phase 6 and not move?  It looks like this time it might hit the wall while in the cold phases for once.  That "could" mean an extended period of cold.  If you like really LR thinking, I have to wonder if it can get through the warm phases(before winter fades) if it exits the cold phases in late December or early January.  I think it can...and probably by the last third of January.  That would give us two decent shots of cold if one assumes winter comes back during that last week of January.  But that second cold shot can be difficult, but the QBO may help us in that regard.

 

[Daniel Boone]

17 minutes ago, Carvers Gap said:

MJO stuff...First off, that is not a warm look for December.  In fact, it kind of just crawls through the left side of the plot which is not something we have seen in recent years.  It seems like the MJO almost defaulted to 4, 5, and 6.  How many times have we seen the MJO hit the wall in phase 6 and not move?  It looks like this time it might hit the wall while in the cold phases for once.  That "could" mean an extended period of cold.  If you like really LR thinking, I have to wonder if it can get through the warm phases(before winter fades) if it exits the cold phases in late December or early January.  I think it can...and probably by the last third of January.  That would give us two decent shots of cold if one assumes winter comes back during that last week of January.  But that second cold shot can be difficult, but the QBO may help us in that regard.

 

   Makes sense imo. The solid wall to wall Winter's did basically what you described. High latitude blocking helped mitigate what trips the MJO made through the warm Phases. In some cases, it would go either low amp through or COD and come back into cold Phases( SST'S were supportive of that then).

    My guess is as your's, in that the MJO will make it back to warm Phases at some point as the SST'S are still supportive for that to occur at decent Amp. 

     As you noted, the -QBO should help. Also, NATL SST'S have became more favorable in supporting a -NAO. 

[Carvers Gap]

I have like the Euro control of the weeklies.  Meaning that if the ensemble and the control don't match, that is a problem as the control is often right.  It spotted the push back on the colder temps for early December.  It wasn't completely right, but there was a warm front embedded that the ensemble didn't see.  This is this afternoons December map.  I don't use these maps verbatim, but just to get a general sense of what is on the table if the 0z Euro was run past 16 days and all the way to Jan 4th!  The ensemble shows this general depiction but MUCH more washed out - seasonably cold.  It is also important to remember that seasonal cold at range...is probably colder in reality.  -15F departures (relative to norms) is insane for a 30 day map.

edit:  To me, that is showing signs of the stratospheric warming as the latter part of that run is brutally cold in the lee of the Canadian Rockies.  We see that often w/ strat warms.  Cold dumps west and spreads east.  The last week of this run is almost 40 BN in the Rockies.  Notice those aren't reflected strongly on this map...it had to eras some warm departures in those places.

[Carvers Gap]

Here is the Euro Weeklies 30 day map centered on December(the above is Dec3-Jan4).  This one is Dec1-Dec31.  I have also included the CFSv2 which ran at lunch.  Where that EPO ridge sets up in the eastern Pac is important.  HL blocking near Greenland is not as important in December as it is in Jan/Feb.  But it would only accentuate potential for cold.  As John noted, the real risk is cold/dry.  The good thing is that models are showing some AN heights over FL.  That would imply that rain/snow would run a path from say TX/LA to  DC.  Storm tracks could be the Ohio Valley if the pattern relaxes or the Piedmont if the cold presses.

edit:  the slight area of an heights over the Gulf states is not a bad thing.  Overall, temps in our area are seasonable BN.  The storm track will likely ride that boundary.  I suspect(if the mean is correct), MUCH colder temps would head southward.  That EPO ridge is nearly perfect for sever cold outbreaks.

 

[Carvers Gap]

For now(and famous last words as we have been fooled many times over the years by December cold on modeling which didn't verify in reality), there is a decent signal for a cold December.  Will it be stormy?  Well, we honestly maybe don't want the severity of cold shown, but the opportunity for NW flow events and for Gulf systems to attack the base of the trough are probably embedded in a pattern like that.

[Daniel Boone]

I always hated to see a Trough dig deep into the SW. Without blocking that generally pumps the SER. With blocking you can get overunning or Waves eject Eastward that pay dividend's. However, with a -EPO you can sometimes get cold highs drop down east of that SW trough and get cold but, usually dry. The above Depictions Carver posted are showing good progression. Somewhat of a SER can be good for our Area as Carvers noted. Waves ride along that Boundary. Just my Antique 2 Cents worth. 

[Carvers Gap]

Precip is AN on the mean and all over the place on the control.  The control implies good precip for western areas of the forum(remember the boundary) and then again for coastal areas from Georgia to the MA late in December.  E TN and W NC would be BN for precip if the control is correct.  If the mean is correct, the entire forum is BN w/ temps and AN for precip.  I think the cold is under modeled at this point - I didn't think that a few days ago and my mind can change on that again.  If it is, the storm track is along the spine of the Apps.

[Carvers Gap]

1 minute ago, Daniel Boone said:

I always hated to see a Trough dig deep into the SW. Without blocking that generally pumps the SER. With blocking you can get overunning or Waves eject Eastward that pay dividend's. However, with a -EPO you can sometimes get cold highs drop down east of that SW trough and get cold but, usually dry. The above Depictions Carver posted are showing good progression. Somewhat of a SER can be good for our Area as Carvers noted. Waves ride along that Boundary. Just my Antique 2 Cents worth. 

The mean doesn't have dump into Texas.  In fact, it might have the trough too far to the East.  Right now(and I know you know this...but this is for new folks), it is so tough to know the trough axis at this range - IDK at this point.  Some modeling is just sending the cold straight to Texas.  Some tends to send into the SE or NE and the MA.  I would suggest the MJO is driving that along w/ the SSW.  If that MJO stalls, we all will probably be just wanting it to warm-up.  In my mind, I see a cold shot after Thanksgiving, a warm-up, another cold shot around the 3rd which means business....and the cold keeps on coming until about Christmas when the pattern moderates.  The danger is that some modeling does not want to moderate after Christmas.  There is a small camp of model runs which deepens the cold to enter January.  In fact, seasonal cold is the warmest those runs get w/ well BN being the base pattern.  Now, I hate even to mention that on a forum.  If it doesn't happen, the disappointment is tough for some....and that hasn't happened since maybe 09-10  But it is worth noting.  Those runs aren't quite outliers either.  The MJO above would support some of those runs.  The interesting thing is if the MJO were to loop back into the cold phases w/ no tour through the warm phases...we haven't seen that type of plot recently.  Plus, there is the rare tour-de-warm MJO that never gets warm.  This is IMHO is class -QBO territory in terms of analogs.

[Carvers Gap]

What is even wilder, a lot of higher elevation folks are already on the board.  I am even on the board w/ 0.5" of snow already, and w/ a NW flow event to boot!