2025-2026 ENSO

[Terpeast]

It looks like GEFS is trying to loop back into 7/8 after its u-turn into 6. Hovmollers shows this as well.

[MJO812]

28 minutes ago, Terpeast said:

It looks like GEFS is trying to loop back into 7/8 after its u-turn into 6. Hovmollers shows this as well.

The EPS couldn't be more clear about phase 8. Expect the coldest part of December in the 2nd half.

 

[PhiEaglesfan712]

2 hours ago, EastonSN+ said:

Do we know exactly what is causing the warmer WPAC ocean temps (as opposed to any other region like CPAC or EPAC)?

I'm not sure exactly what is causing the warmer WPAC ocean temps. All I know is that something must have happened in between the 2009-10 strong el nino and the 2015-16 super el nino.

[anthonymm]

7 minutes ago, PhiEaglesfan712 said:

I'm not sure exactly what is causing the warmer WPAC ocean temps. All I know is that something must have happened in between the 2009-10 strong el nino and the 2015-16 super el nino.

2009-2010 strong la nina *

[donsutherland1]

6 minutes ago, anthonymm said:

2009-2010 strong la nina *

2009-10 was a strong El Niño. 2010-11 was a strong La Niña.

[EastonSN+]

18 minutes ago, PhiEaglesfan712 said:

I'm not sure exactly what is causing the warmer WPAC ocean temps. All I know is that something must have happened in between the 2009-10 strong el nino and the 2015-16 super el nino.

I don't think we can determine which factor will eventually cool the WPAC until we can pinpoint what is causing it (as opposed to other areas).

[michsnowfreak]

I know things are looking decent when we are seeing embedded tweets in French.

[LakePaste25]

10 minutes ago, EastonSN+ said:

I don't think we can determine which factor will eventually cool the WPAC until we can pinpoint what is causing it (as opposed to other areas).

It is due to climate change. The trade winds unevenly distribute the warmer water to the western pacific. This phenomenon only temporarily bounces back during El Niño years, and doesn’t even fully do this anymore. It’s here to stay. 

[GaWx]

 With the unfavorable changes in the MJO and AO/NAO, today’s 0Z GEFS is not surprisingly significantly warmer than yesterday’s run for the 2nd week in Dec. However, today’s 0Z EPS, which maintained its very long phase 8, is much colder than yesterday as well as the GEFS:

Yesterday’s 0Z EPS for 12/5-11 2m temps:

 

 Today’s 0Z EPS for 12/5-11: it’s pretty rare for a 7 day period of the EPS to have that much of a change within just 24 hours:

 As a result, the aggregate of today’s Euro Weeklies 12/1-7 and 12/8-14 2m temp anomaly maps will very likely be notably colder than yesterday’s.

[GaWx]

1 hour ago, donsutherland1 said:

Yesterday, I noted that the GEFS was trying to push an EPO+, but its forecast 500 mb pattern was profoundly different from any of the December WPO-/EPO+/AO-/PNA- clusters. That suggested that either the teleconnection idea was off or the pattern was off, rather than some novel outcome. 

Overnight and through today's 6z cycle, the GEFS has continued to evolve. It has added a WPO+ to its EPO+ idea and restored its earlier idea of a AO+. It has now joined the Canadian ensembles that keep the MJO out of Phase 8 through its forecast horizon. In short, its previously significant areas of "disconnect" have disappeared overnight. Its forecast pattern is now more consistent with what one would expect.  For now, the GEFS is trying to build a credible milder alternative scenario for the pattern/temperature evolution in North America toward mid-December. 

The EPS has not shifted toward that emerging GEFS idea. Therefore, the baseline idea remains that the northern tier of the U.S. and most of Canada should remain cold toward and probably beyond mid-December. The Southeast could still turn warm despite some shots of colder air.  

Mid-December and beyond is still in the low-skill distant realm. The big story through the weekend will be the significant snowstorm that will affect parts of the Midwest and Great Lakes Region. As a result, Chicago, Detroit, Milwaukee, and Toronto remain on track to experience their snowiest fall in five or more years. As an appetizer, Detroit added 0.1" snowfall yesterday and Toronto picked up 1.2 cm (0.5") yesterday.

Related to this, check out the differences in the means (green) between the +AO of the 0Z GEFS and the slight -AO of the EPS:

GEFS:

 

EPS:

 

[Terpeast]

1 hour ago, donsutherland1 said:

Yesterday, I noted that the GEFS was trying to push an EPO+, but its forecast 500 mb pattern was profoundly different from any of the December WPO-/EPO+/AO-/PNA- clusters. That suggested that either the teleconnection idea was off or the pattern was off, rather than some novel outcome. 

Overnight and through today's 6z cycle, the GEFS has continued to evolve. It has added a WPO+ to its EPO+ idea and restored its earlier idea of a AO+. It has now joined the Canadian ensembles that keep the MJO out of Phase 8 through its forecast horizon. In short, its previously significant areas of "disconnect" have disappeared overnight. Its forecast pattern is now more consistent with what one would expect.  For now, the GEFS is trying to build a credible milder alternative scenario for the pattern/temperature evolution in North America toward mid-December. 

The EPS has not shifted toward that emerging GEFS idea. Therefore, the baseline idea remains that the northern tier of the U.S. and most of Canada should remain cold toward and probably beyond mid-December. The Southeast could still turn warm despite some shots of colder air.  

Mid-December and beyond is still in the low-skill distant realm. The big story through the weekend will be the significant snowstorm that will affect parts of the Midwest and Great Lakes Region. As a result, Chicago, Detroit, Milwaukee, and Toronto remain on track to experience their snowiest fall in five or more years. As an appetizer, Detroit added 0.1" snowfall yesterday and Toronto picked up 1.2 cm (0.5") yesterday.

AIFS ensembles have also been performing well with the polar domain's 500mb patterns, and both it and EPS have been trending less positive with the AO in recent runs. Otoh, GEFS has been verifying better with the MJO. Something to watch for.

[EastonSN+]

39 minutes ago, LakePaste25 said:

It is due to climate change. The trade winds unevenly distribute the warmer water to the western pacific. This phenomenon only temporarily bounces back during El Niño years, and doesn’t even fully do this anymore. It’s here to stay. 

Maybe I need a visual, however, why are the trade winds distributing specifically to the WPAC? Also does that mean the EPAC will remain generally cooler than average due to upwelling?

[Terpeast]

10 minutes ago, Terpeast said:

AIFS ensembles have also been performing well with the polar domain's 500mb patterns, and both it and EPS have been trending less positive with the AO in recent runs. Otoh, GEFS has been verifying better with the MJO. Something to watch for.

Actually, EPS has been catching up with MJO verification in the last week or so. It did horribly when it was in phase 6, but much better once we crossed into 7.

[LakePaste25]

1 hour ago, EastonSN+ said:

Maybe I need a visual, however, why are the trade winds distributing specifically to the WPAC? Also does that mean the EPAC will remain generally cooler than average due to upwelling?

Walker circulation and yes. It’s why relative ONI (RONI) is used frequently here, because the eastern equatorial pacific warming relatively slower than the rest of the pacific is amplifying La Niña and also weakens the signal of El Niño to some extent. 

Walker circulation: https://www.climate.gov/news-features/blogs/enso/walker-circulation-ensos-atmospheric-buddy

[GaWx]

Indeed, after doing poorly with phase 6, the EPS absolutely was doing much better than GEFS getting into phase 7 between the 11/15 and 11/18 runs:

11/15 EPS: poor for 6; much better for getting into 7

11/15 GEFS: great for 6 but bad for getting into 7 (way too slow as 7 actually started on 11/27):

 

Similar comparisons for 11/17-8 runs:

11/17 EPS: almost spot on with 11/27 ph 7 timing:

11/17 GEFS: still not in 7 on 12/1

 

11/18 EPS: great with ph 7

 

11/18 GEFS: not into phase 7 til 12/2, 5 days too late

 

Edit: 12Z GEFS coming in significantly colder than prior runs

[snowman19]

Yesterday, I noted that the GEFS was trying to push an EPO+, but its forecast 500 mb pattern was profoundly different from any of the December WPO-/EPO+/AO-/PNA- clusters. That suggested that either the teleconnection idea was off or the pattern was off, rather than some novel outcome. 
Overnight and through today's 6z cycle, the GEFS has continued to evolve. It has added a WPO+ to its EPO+ idea and restored its earlier idea of a AO+. It has now joined the Canadian ensembles that keep the MJO out of Phase 8 through its forecast horizon. In short, its previously significant areas of "disconnect" have disappeared overnight. Its forecast pattern is now more consistent with what one would expect.  For now, the GEFS is trying to build a credible milder alternative scenario for the pattern/temperature evolution in North America toward mid-December. 
The EPS has not shifted toward that emerging GEFS idea. Therefore, the baseline idea remains that the northern tier of the U.S. and most of Canada should remain cold toward and probably beyond mid-December. The Southeast could still turn warm despite some shots of colder air.  
Mid-December and beyond is still in the low-skill distant realm. The big story through the weekend will be the significant snowstorm that will affect parts of the Midwest and Great Lakes Region. As a result, Chicago, Detroit, Milwaukee, and Toronto remain on track to experience their snowiest fall in five or more years. As an appetizer, Detroit added 0.1" snowfall yesterday and Toronto picked up 1.2 cm (0.5") yesterday.

The GEFS is insistent on putting a huge 500dm vortex right over Alaska the 2nd week of December. Several runs in a row now 

https://www.pivotalweather.com/model.php?m=gefsens&p=500h_anom-mean&rh=2025112812&fh=282&r=na&dpdt=&mc=&pwplus=1

[EastonSN+]

17 minutes ago, LakePaste25 said:

Walker circulation and yes. It’s why relative ONI (RONI) is used frequently here, because the eastern equatorial pacific warming relatively slower than the rest of the pacific is amplifying La Niña and also weakens the signal of El Niño to some extent. 

Walker circulation: https://www.climate.gov/news-features/blogs/enso/walker-circulation-ensos-atmospheric-buddy

Wondering if other factors are negating the effects of the typically warm phases of the MJO (laster year was cold despite the MJO). Perhaps the responses we are used to seeing  historically will no longer be the case..

[GaWx]

4 minutes ago, snowman19 said:

The GEFS is insistent on putting a huge 500dm vortex right over Alaska the 2nd week of December. Several runs in a row now 

12Z GEFS is coming in significantly colder than the 0Z for week 2:

 

[EasternLI]

1 hour ago, EastonSN+ said:

I don't think we can determine which factor will eventually cool the WPAC until we can pinpoint what is causing it (as opposed to other areas).

There is, perhaps, something else to consider in the context of that. The IPO or Interdecadal Pacific Oscillation. Being an interdecadal phenomenon, it operates on timescales of multiple decades. This complicates matters. It's easy to perceive something potentially spanning over a decade as being permanent. It also encompasses the entire Pacific basin. Whereas features such as Enso and the PDO are more geographically focused and can fluctuate within the greater framework spanning multiple decades. There's a lot to read out there on the topic. 1st image below is from the NOAA Physical Sciences Lab showing the positive phase of the IPO and associated tripole signature. Interestingly, there have been some research done suggesting links between the record 2019-20 Australian wildfires and the IPO. Perhaps enhancing a negative phase along with playing a role in our most recent triple dip la nina event. By altering cloud physics. 2nd image is what we have currently. Showing a pretty clear -IPO on going to this day. One day this will shift again. My guess is that we'll see the marine heatwaves that we hear about shift as well when that happens.

+IPO:

 

Current conditions:

[snowman19]

4 minutes ago, GaWx said:

12Z GEFS is coming in significantly colder than the 0Z for week 2:

 

That wasn’t my point. I was responding to Don’s post that the GEFS is insistent on a +EPO pattern taking hold the 2nd week of December, which it clearly is. It’s putting a huge vortex over Alaska and has been for several runs in a row

[LakePaste25]

20 minutes ago, EastonSN+ said:

Wondering if other factors are negating the effects of the typically warm phases of the MJO (laster year was cold despite the MJO). Perhaps the responses we are used to seeing  historically will no longer be the case..

Yes, there’s research out there that the Indo-pacific warm pool can contribute to western ridging/eastern trough, sometimes even independent of ENSO. Lots of research out on this topic:

 

https://journals.ametsoc.org/downloadpdf/view/journals/clim/29/22/jcli-d-16-0145.1.pdf

 

https://repository.library.noaa.gov/view/noaa/48389/noaa_48389_DS1.pdf

[snowman19]

1 hour ago, snowman19 said:

That wasn’t my point. I was responding to Don’s post that the GEFS is insistent on a +EPO pattern taking hold the 2nd week of December, which it clearly is. It’s putting a huge vortex over Alaska and has been for several runs in a row

And just to add to this, if (IF) the GEFS is correct that a +EPO/Alaskan vortex pattern takes shape the 2nd week of December, it makes perfect sense that there will still be cold in the CONUS and Canada at that point. It’s not a light switch flip to immediate warmth, that would come later. A +EPO would cut off cross-polar flow and the Pacific floodgates would open. It would take some time for all the cold to get scoured out of Canada and the CONUS but it would happen, again, assuming the GEFS has the right idea  @donsutherland1

Edit: @brooklynwx99 Yes it would be serviceable for awhile until the cold got scoured out, but eventually all a -NAO block would do in the GEFS scenario (+EPO/AK vortex) is trap Pacific maritime air underneath the block 

[brooklynwx99]

even with said AK vortex (which seems suspect), it’s still cold with a -NAO popping up. this would still be serviceable for a while, and this seems like the worst case scenario through the 10th. EPS and GEPS are much colder with +PNA

[stadiumwave]

12z EPS has persistent cold for though the end. 

[MJO812]

3 minutes ago, stadiumwave said:

12z EPS has persistent cold for though the end. 

Phase 8 December

Haven't seen that in years

[MJO812]

[MJO812]

Cold is coming 

[MJO812]

Weeklies

[bluewave]

Split forcing between the Maritime Continent and the Western Hemisphere appears to be causing an interference pattern resembling a phase 6 in early December.

It could also be why the models have been showing so much volatility between runs over the last week as we head into December.

A  Northeast Pacific  +TNH with a a cold upper low centered near Hudson Bay more closely resembles a phase 6 composite.

So trying to guess what composite or pattern we end up with in mid to late December is anyone’s guess at this point.

We will just have to let things play out next few weeks to see which area of forcing eventually wins out. 
 

 

 

[GaWx]

3 hours ago, snowman19 said:

And just to add to this, if (IF) the GEFS is correct that a +EPO/Alaskan vortex pattern takes shape the 2nd week of December, it makes perfect sense that there will still be cold in the CONUS and Canada at that point. It’s not a light switch flip to immediate warmth, that would come later. A +EPO would cut off cross-polar flow and the Pacific floodgates would open. It would take some time for all the cold to get scoured out of Canada and the CONUS but it would happen, again, assuming the GEFS has the right idea  @donsutherland1

Edit: @brooklynwx99 Yes it would be serviceable for awhile until the cold got scoured out, but eventually all a -NAO block would do in the GEFS scenario (+EPO/AK vortex) is trap Pacific maritime air underneath the block 

For Dec 1-10:

12Z EPS held onto its 0Z significantly colder temps vs 0Z GEFS.

But also, 12Z GEFS came in significantly colder than 0Z GEFS:

0Z GEFS:

12Z GEFS: colder/in EPS direction:

12Z GEPS came in much colder than 0Z GEPS:

0Z GEPS:

 

12Z GEPS: colder than 0Z GEPS