2025-2026 ENSO

[GaWx]

Folks,
 I recommend that snowman and others not look at the Euro Weeklies today. I’d instead go outside and enjoy the fantastic Canadian air! And Happy New Year! May 2026 be dominated by more Canadian air! Keep in mind that the EW are essentially the extended 0Z EPS. The 12Z EPS trended better with the western ridge and that won’t be reflected on the EW.

[40/70 Benchmark]

23 hours ago, GaWx said:

 This was released by BAMwx:

 

 Thoughts? I’m going to need to research this myself to feel comfy with BAMwx’s idea of the highly counterintuitive idea of a very cold E US on average during La Niña (-AAM) Jan phase 6 periods. They’re saying this probably because GEFS is forecasting phase 6 going into mid-Jan as per my earlier MJO forecast post. I can do the analysis but it will take time. I’m planning to look at actual temp anoms for a city like ATL, Chat., Nashville, or GSP that’s in the heart of the coldest (pink) for all phase 6 days during Jan since 1975. Actually anyone can do it but one needs lots of time to do this.

In the meantime, I’ll continue to root for weak to moderate 8-1-2 over 6 or even 7.

@donsutherland1@bluewave

Perhaps these excerpts from my outlook last fall will prove somewhat illuminating....
Lee et al (2019) identified the transition from this Pacific trough regime to the Alaskan ridge regime as most conducive to the type of wave propagation needed to trigger a reflection event, which renders the Pacific trough regime the precursor pattern. This is a remarkable extended forecasting tool given the expectation for a mid January onset of a reflection event, as this implies that the first half of January is likely to be mild and characterized by Pacific trough regime with a rapidly consolidating PV, thus the arctic low regime is also worthy of consideration here during this mid-winter-thaw period.

 

 

This period will also feature a considerable Pacific jet extension as mild Pacific air infiltrates the vast majority of the CONUS and flooding becomes a concern for areas that amassed a snowpack during the early season arctic high regime.  Any seasonably cold air masses are likely to be dislodged from the east coast by a primary storm track across the interior. The expected midseason progression is illustrated in the schematic below that details the typical evolution of reflection event. Note that the pattern begins to reverse in earnest approximately 5 days after the event onset, during which time the anonymously strong PV reverts to normal strength, and begins to stretch due to the building Alaskan and Aleutian ridging that retrogrades from North America. 

 

 

This is why it very mild at the onset of these events, during the antecedent Pacific trough pattern, but by ten days post reflection the pattern has reversed and is characteristic of an Alaskan ridge regime (bottom right above). Once the process terminates and run its course by early February, a more canonical La Nina pattern will likely ensue in the absence of the expected SSW. However, should one materialize as anticipated, another arctic high interval is possible for potential grand finale to the season.

[40/70 Benchmark]

Considering the length of the 2001 (33 days) and 2018 (20) events, it as expected that a reflection event will begin between approximately January 13th and 16th 2026, and end between about February 2 and 18th. This is consistent with the climatologically favored time frame per the research that was referenced previously.  In order to better understand how the PV interacts with North American weather,  Lee at al identified four distinct weather regimes and listed their respective frequency of occurrence between the months of November and March, from 1979 through 2017, since they last longer than synoptic scale patterns and thus provide an opportunity for longer range prediction. 

Pacific Trough Pattern Precursor for Reflection Events

 Pattern recognition is paramount in the analysis and diagnosis of reflection events because the behavior of the polar vortex has predictive value on each of these regimes at both seasonal, and sub-seasonal leads, which is roughly 15-60 day in advance. "The PV strength significantly affects the occurrence and persistence of each regime and transition between regimes" (Lee at al 2019). Research by Kretschmer et al (2018) illustrated the importance of planetary wave reflection for anomalous cold across North America. This expounded on earlier work by Kordera et al (2016) that found that wave reflection born of Pacific blocking tele-connected to a down stream trough over North America. Thus the implication here is that the Alaskan ridge pattern, which is not at all connected to the PV and is actually accompanied by a +NAO, as alluded to earlier, is most conducive to reflection events and is this correlated to the most severe arctic outbreaks in the US. Lee et al (2019) refers to this type of pattern as the "Alaskan Ridge Regime" , which is similar to the Tropical Hemisphere Pattern (+TNH).

 

 This has been the most common vehicle for cold delivery over the past decade given the increased tendency for +NAO during the winter season, so it is important to remain mindful of the fact that climate change is certainly not prohibitive to severe cold outbreaks. It does, however, decrease residence time due to the enhanced Pacific jet keeping the flow more progressive.