2025-2026 ENSO

[leo2000]

Brutally cold and snowy winter on the way. I know Don was mentioning about the cold pool is much smaller than in 1968 but this is not arctic air coming it is Siberian cold and with the pdo rising that would increase snowstorm chances. 

[GaWx]

2 hours ago, donsutherland1 said:

There have been some subtle shifts in the guidance. The combination of subtle shifts and long timeframes can lead to big changes. But the timeframe involved is speculative and skill scores at that timeframe are essentially non-existent. 

What remains extremely likely is that a sudden stratospheric warming event (SSWE) is imminent. Zonal winds will slacken dramatically during the next 5-7 days. A full reversal can't be ruled out.

There is typically a lag of 10-30 days for the impact of an SSWE to propagate to the troposphere. So, even as a cold shot appears increasingly likely from the Great Lakes Region to the Northeast to close November, that cold shot will almost certainly not be the result of the imminent SSWE. What happens with the polar vortex (split and location of the pieces) will be crucial. 

For now, things still appear on a path toward an EPO-/WPO-/AO-/PNA- pattern development. Initially the most significant cold appears likely to dump into the Plains States before pushing eastward. The Great Lakes Region still seems primed for a possible multi-week period of below normal temperatures coupled with above normal precipitation. That should lead to an increase in snowfall totals in such cities as Chicago, Detroit, Windsor, and Toronto. 

Pieces of the cold should begin to bleed into the East, but perhaps after the first 7-10 days of December.

If things evolve along this baseline scenario, the December 10-25 period might see the coldest anomalies relative to normal for such cities as Chicago, New York, Philadelphia. The Southeast could see some intrusions of cold, but the PNA- could promote an unwelcome and persistent tendency for SE ridging. Newer guidance suggests an increased probability of a negative NAO, so that could flatten the SE ridge at times. This is my baseline thinking.

IMO, the Week 3-4 CPC Outlooks capture the temperature idea of kind of pattern I expect to prevail during the first half of December. 

Despite social media chatter 1983-style Arctic outbreaks, a lot would need to change for such an outbreak to become likely. Currently, the Northern Hemisphere's cold pool is much smaller than it was at this time in 1983:

2025:

1983:

 

In the very long range, some of the subtle shifts in the teleconnections e.g., dissipation of the WPO-, could translate into the trough's migrating back to the West and a Southeast Ridge reviving in the closing week of December. That's not shown on the weekly ECMWF guidance. But the December 22-29 period's 500 mb forecasts should be monitored for hints of change. It should be noted that neither the MJO nor teleconnections can be forecast with skill at such a forecast horizon.

In sum, wintry opportunities should increase in December, first in Plains States and Great Lakes and then farther East. The Great Lakes Region and Ohio Valley look primed for above normal snowfall during December. The Southeast could have the most difficult time seeing the cold try to gain traction, but some cold shots should eventually break through. The closing week of December looks uncertain. Much depends on how the SSWE's impacts will evolve and other variables that cannot be forecast with skill at that range.  Typical SSWE lags would argue that the breakdown in the pattern might occur later. Then there's always the wild card of additional warming events.

Thanks, Don. One thing helping 2025 vs 1983 is that 1983 didn’t have a weak SPV as it didn’t get <15 m/s through Nov and Dec:

[stadiumwave]

2 hours ago, GaWx said:

Today’s GEFS gets to phase 7 a day earlier than yesterday’s (11/28 vs 11/29) and three days earlier than the run from 2 days ago.

 The 11/19/25 Euro-ext gets it to phase 8 ten days earlier (12/5) than the prior run (12/15):

Prior run (11/18/25):

 

Nearly a guidance is going more amped through 7 & then moving into 8 now. Canadian output is the lone exception 

[das]

On 11/19/2025 at 11:40 AM, donsutherland1 said:

The idea of an imminent SSW/MSW event is a high-confidence one. However, there is often a tendency to treat forecast developments (“SSW → PV split → EPO-/WPO-/AO-/PNA- → brutal NE weather”) as if it were an inevitable, linear, cause-and-effect chain. If such logic were reliable, forecasting accuracy at multi-week stages would be high. That isn't the case.

I personally believe that there will be an increase in wintry effects, especially from near mid-December into at least late December based on typical 1-3 week lags and the currently forecast teleconnection evolution.  That's my baseline thinking at present.

However, that thinking isn't cast in stone. Reality is messier. For example, not every SSW leads to a prolonged deep AO-. Not every AO- period results in severe cold and/or excessive snowfall. 

From this far out, model skill is poor to non-existent on critical synoptic factors e.g., future storm tracks, the emergence of North Pacific jet streaks, exact ridge-trough placement, etc. A bad pattern coupled with a well-timed phase can produce a big snowstorm; a great pattern but badly-timed phases or absence of shortwaves can result in a lack of snowfall. Seemingly favorable ensemble means can also disguise large differences among ensemble members.  Clusters can provide insight into some scenarios.

For now, potential is on the table. But nothing is locked in, just yet, in terms of specific details.

Great post @donsutherland1.  I, for one, am looking forward to shoveling inches and inches of pattern.  

Back to lurking for me...

[bluewave]

16 minutes ago, stadiumwave said:

 

Nearly a guidance is going more amped through 7 & then moving into 8 now. Canadian output is the lone exception 

The RMM charts are only providing part of the picture. They are following the convection to the east of the Dateline. But we still have convection lingering near the Maritime Continent into early December. So it’s more of a split forcing pattern rather than a canonical MJO driven pattern.