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Pattern December Doldrums 2025 🎄 ❄️

That 12z euro was brutal with the SE RIDGE
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Today’s Euro Weeklies 10 mb 60N zonal wind isn’t as weak as recent runs:

Today’s run (11/19):
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Yesterday’s (11/18):
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Does anyone else see what I’m referring to? I’m not just talking about whether it actually reverses. I’m talking more about the period afterward. That’s a notable change in the stronger direction.

Today’s Euro Weeklies 10 mb zonal wind mean is slightly weaker early and allows most to reverse unlike yesterday. However, afterwards it looks like yesterday’s significantly stronger run:

Today’s
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Yesterday’s:
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Two days ago: significantly weaker
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Today’s Euro Weeklies vs yesterday for SE US are ~same for 12/1-14 with a strong SER 12/1-7 followed by a slow weakening of it to a weaker 12/8-14. But 12/15-21 is slightly cooler with NN instead of slightly warmer than normal. 12/22-28 is slightly cooler with still NN most of SE but slightly colder than normal N NC. The new week, 12/29-1/4 is NN in the SE.
 
A whopping nearly 80% of 3+ day long Dec phase 8 periods averaged colder than normal at Raleigh though with lots of variation. When amplitude is <1.5, that rises even further to 85% along with an average of 5.0 F BN. If it’s a pretty strong amplitude (1.5+), it actually averaged only 0.5 F BN at Raleigh. Fortunately, most Dec phase 8 are <1.5 amp.

The coldest Dec phase 8 periods at RDU were all with <1.5 amp:

- 13 F BN 12/9-18/1989: 1.9” mix/ZR (2 events)
- 13 F BN 12/5-9/2002: a major ZR
- 12 F BN 12/20-25/1995 no wintry precip
 
Good combination here! We need the rain! A lot of D1-D2 conditions here as of yesterday! IMG_3337.jpegIMG_3338.jpeg
 
The low-level (850 mb) wind is what's really driving the MJO into phase 8 at least on the GFS/GEFS & CFS

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One reason I really love looking at hovmoller diagrams (like the Euro weekly forecast below) is you can easily spot some of the reasons behind why the RMM MJO does these "loop de loops". A lot of that in this case has to do with convectively coupled kelvin waves quickly amplifying and damping as they move in and out of the MJO envelope

Screenshot 2025-11-21 at 6.58.10 AM.png
 
While here in the SE it appears certain we will be waiting impatiently for cold weather the first week of December, the stage is being set for good times shortly thereafter IMO. We're replacing the currently above-normal temps across the whole of the N. The American Continent with much-below-normal temperatures across the whole of Canada and the US Midwest while laying down snowcover and accelerating Hudson Bay and Great Lakes icing.

Winter is coming.
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The 6 coldest La Niña to neutral ENSO Decembers in the E US as a whole since 1974 have been 1983, 1985, 1989, 2000, 2005, and 2010:
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Here are the respective Dec MJOs:

1983: mainly inside COD or just outside/no strong
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1985: almost all inside COD
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1989: most of 8/1 just outside COD or inside it/no strong
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2000:almost all just outside or inside COD
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2005: all inside COD
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2010: all just outside or in COD
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What do these 6 have in common regarding the MJO? No strong and most days just outside to inside COD.

Regarding the extended progs that have the Dec 1-21 MJO: note how strong they are, especially GEFS but even the Euro is solid compared to the six cold Decembers posted. My concern is that the MJO amplitude will be too strong, based on history, to allow for a widespread intense cold dominated E US in Dec. Thus, I’m hoping the progs remain going into 8, but weaken. My hypothesis as to why strong MJO has had a tendency (though not always, of course) to not be as cold as weaker MJO is because the higher amp may tend to bring up too much warmth from the tropics, where the MJO is measured
 

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The 6 coldest La Niña to neutral ENSO Decembers in the E US as a whole since 1974 have been 1983, 1985, 1989, 2000, 2005, and 2010:
View attachment 176993

Here are the respective Dec MJOs:

1983: mainly inside COD or just outside/no strong
View attachment 176994

1985: almost all inside COD
View attachment 176995

1989: most of 8/1 just outside COD or inside it/no strong
View attachment 176996

2000:almost all just outside or inside COD
View attachment 176997


2005: all inside COD
View attachment 176998

2010: all just outside or in COD
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What do these 6 have in common regarding the MJO? No strong and most days just outside to inside COD.

Regarding the extended progs that have the Dec 1-21 MJO: note how strong they are, especially GEFS but even the Euro is solid compared to the six cold Decembers posted. My concern is that the MJO amplitude will be too strong, based on history, to allow for a widespread intense cold dominated E US in Dec. Thus, I’m hoping the progs remain going into 8, but weaken. My hypothesis as to why strong MJO has had a tendency (though not always, of course) to not be as cold as weaker MJO is because the higher amp may tend to bring up too much warmth from the tropics, where the MJO is measured

Seems to be the sweet spot from your research, low phase 8, COD on the 8 side. Hopefully that comes to fruition. The models right now are just saying phase 7 is not it for the SE. Pacific jet does not want to push east and is a little nubby, causing the SE ridge to keep us nice and warm while the mid west gets nice and cold (classic -EPO/-PNA). Need that to extend east to HI and all the reds in AK/out west to kick east.

In two weeks though when December actually starts, I bet it completely different, one way or another. Hopefully to a classic weak 8.

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not breaking any news here, just pretty remarkable to me how well things line up with mjo phase and current 8-14 day analogs. simply taking the current top ten of those, you get a noticable SER signal for Dec

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throw january in the pot and it starts to even out. january alone is within 0.5F for the SER zones and BN for the rest of the country

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Presented without comment...

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the good news is, the latest AIFS is the most aggressive yet in the LR as far as bleeding cold eastward towards the end of the first of Dec.
the bad news is, this is a single model run and the ridgey analog + latest ensembles continue to support SER.
i still feel like that's a thing worth watching. it's been said already that we could be in for a bit of a roller-coaster ride, and the AIFS supports that for sure. need some ens support to show up though, while it did lead the way on the upcoming turkey day front, there was some ens support at the same time
 
Unlike the SE US where you can get CAD, overunning, coastal events, etc. there’s really only one recipe that can give us a good snow event in New Mexico and this longwave pattern isn’t too far off from that in early December.

So many ways to screw this up but I’m at least intrigued.

Regardless, this should be a nice table setter event over the conus to get the cold well established and deeply entrenched

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Unlike the SE US where you can get CAD, overunning, coastal events, etc. there’s really only one recipe that can give us a good snow event in New Mexico and this longwave pattern isn’t too far off from that in early December.

So many ways to screw this up but I’m at least intrigued.

Regardless, this should be a nice table setter event over the conus to get the cold well established and deeply entrenched

View attachment 177012
Go on & reel ya one in Eric.
 
Unlike the SE US where you can get CAD, overunning, coastal events, etc. there’s really only one recipe that can give us a good snow event in New Mexico and this longwave pattern isn’t too far off from that in early December.

So many ways to screw this up but I’m at least intrigued.

Regardless, this should be a nice table setter event over the conus to get the cold well established and deeply entrenched

View attachment 177012
Great pattern for you
 
Today’s Euro Weeklies update on the SPV compared to last run keeps the reversal (or near reversal) but it’s a fair bit stronger Dec-early Jan. Keep in mind that the prior two runs were already significantly stronger for that period:

Today’s EW mean zonal wind at 10 mb (11/21): significantly stronger than 11/18 run with, for example, 12/12 at +29 vs +11 on 11/18 run:
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EW run from just 3 days ago (11/18): 12/12 had been at only +11:
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