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.

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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.