2024-2025 La Nina

[40/70 Benchmark]

14 minutes ago, bluewave said:

It’s interesting that we may have both found our way to the Pacific blocking through different means. I was mentioning the mismatch potential back in October with the high amplitude MJO 5 leading to less MJO influence early on in December like we are seeing now.  But I wasn’t sure whether it would manifest in December as +PNA, -EPO, or -WPO. It’s good that we can use different approaches and come to a roughly similar conclusion of more blocking on the Pacific side to start December than recent years. The complicating factor I mentioned is that the mismatch  is occurring against a much weaker La Niña state than 2020, 2017, and 2010. So we may see more of a competing influence going foreword than those stronger La Niña years. It’s possible we may see a stronger MJO influence later on which would add another competing influence to the mix. It will be fun to see how it goes.

I incorporated your methodology to add confidence to the general mismatch idea, but I honed in on the WPO due to an area of anomalus warmth over the western Pacific.

I do think we will see more competing influences over the course of the season. I thought January would be the most wintry month, but perhaps it will be December, instead.

[Allsnow]

 

[Snowstorms]

4 hours ago, bluewave said:

You can see the blending of the influences in the emerging model trends for the start of December. The +AAM spike introduced the high latitude blocking on the Pacific side. But we still have a lingering La Niña influence with the jet trying to split the ridge near Alaska between the -WPO and +PNA. What may happen is that one of these jet disturbances is strong enough to cause a relaxation of the pattern mid to late December. But if this neutral ENSO state continues into January, then we could get follow up Pacific blocking at that time which would help to erode the -PDO.

New run ridge slight lower -EPO ridging stronger jet

Old run more consolidated block weaker jet

 

 

 

 

How is the most recent -PDO pattern (2019 - present) different than prior -PDO periods (i.e., 2005-2014 or 1960-1976) that featured more prominent cold winters? Perhaps the marine heatwave is having an effect on the PDO? 

[George001]

3 hours ago, snowman19 said:

@bluewave @donsutherland1 While a big curveball has been thrown with respect to the PAC, the stratospheric/SPV progression so far is not conducive to sustained AO/NAO blocking going into December, not that we need them to be with a PAC like that come early December
 

Often winter shows its hand early. We are seeing signs of both a somewhat resilient Alaskan ridge regime and a strong PV regime. It’s early, but if this continues into winter it would lead to a -EPO/+NAO look.

[donsutherland1]

2 hours ago, uofmiami said:

Webber has a thread this morning on what he thinks is driving pattern and it’s not the MJO:

 

I agree with his assessment. The MJO is currently in Phase 3 at a high amplitude. As it moves into and through the Maritime Continent, one would generally expect warmth in the East. The MJO's impact can be offset by other variables.

[PhiEaglesfan712]

27 minutes ago, Snowstorms said:

How is the most recent -PDO pattern (2019 - present) different than prior -PDO periods (i.e., 2005-2014 or 1960-1976) that featured more prominent cold winters? Perhaps the marine heatwave is having an effect on the PDO? 

I think rapidly increasing climate change is a huge factor in the difference between the 2005-2014 -PDO cycle compared to the current -PDO cycle. Keep in mind, 2009-10 and 2023-24 had similar ENSO states, yet 2009-10 was a cold and very snowy winter, while 2023-24 was a very warm winter. I think the Earth being 0.5C warmer in 2023-24, compared to 2009-10, is a huge reason for the differences.

[bluewave]

59 minutes ago, Snowstorms said:

How is the most recent -PDO pattern (2019 - present) different than prior -PDO periods (i.e., 2005-2014 or 1960-1976) that featured more prominent cold winters? Perhaps the marine heatwave is having an effect on the PDO? 

The most recent -PDO from 2019 through 2024 has been defined by an extreme marine heatwave probably enhancing the feedback loop between the SSTs and 500 mb pattern. You can see how much cooler past -PDO periods were. So if this present pattern represents the beginning of a shift back to +PDO, then my guess it will be more defined by marine heatwave feedbacks than the earlier +PDO periods were. But we would need to see the low pressure north of a Hawaii lock in past early December to have a shot at altering the current -PDO SST state. As I said earlier in this thread, the atmospheric pattern leads the SST PDO pattern. Only time we’ll tell if this is just a blip that reverts back or we reshuffle the Pacific pattern with the marine heatwaves moving around from the most recent period since 2019.

Theoretical future +PDO state driven by marine heatwaves

 

[donsutherland1]

4 hours ago, snowman19 said:

@bluewave @donsutherland1 While a big curveball has been thrown with respect to the PAC, the stratospheric/SPV progression so far is not conducive to sustained AO/NAO blocking going into December, not that we need them to be with a PAC like that come early December
 

I suspect that the strengthening PV and lagged response to the development of an AO+/NAO+ will increase the risk for warming late in December. It will take some time to scour out the cold that will dominate during the first half of the month, especially when the PNA is positive.