Stormchaserchuck1

I think it's because there is a trough over Alaska.. I've noticed over the years that they have weight on Alaska and Gulf of Alaska for PNA measurement

Looking back, when the East coast was super dry May-June, and the cap wasn't breaking for anything, that should have been a good signal that the tropics wouldn't be as wet.

No way should that be a +PNA.. not only that but it's >1, with one of the larger index readings in the last few months. ' Last Winter was also classified +PNA, when there was definitely an Aleutian ridge over their "blue" region. This messes me up, because I use their correlation composites, to run together different patterns +lag/lead times.. if they aren't classifying N. Pacific ridges right, it could give some silly and unwanted results.

+NAO has a slight correlation with higher SLP and cooler SSTs. I guess this is what they are referring to In September, the wavelengths are so short that there is actually a slight lower SLP correlation in the hotter tropical region We should be having a -NAO by late September

There have been plenty of active seasons with +NAO's before. The thing is, Sept 12th is midway through the season and we are on "G", which is the 7th storm. On pace for 13-14. For a very long time, the Atlantic average 9 NS/yr. The better thing to look at is "what wasn't anomalous this season". Assume that the last 30 years have been an anomaly, with the Atlantic having 180% ACE, and the whole globe together having 74% ACE.

The Euro did have 200% moisture in the Caribbean for ASO.. that's not verifying for sure. I have been impressed though at how we very rarely see a total disconnect from these modeled seasonal H5 patterns.

That is disconnecting too.. TAO/Triton is not nearly as impressive.

Pretty good -NAO/-AO on the LR 00z GEFS. This is the only time of year where we don't want it to happen!

I saw this posted too: I think the Euro has a 0.65-0.70 seasonal forecast correlation. Even though it had the ridge too far north last Winter, it did come within hundreds of miles of a record breaking ridge that did take place. It also had a good Summer LR forecast for heat in the NE. The Euro isn't perfect, but it usually does generally come within a general range area.. that below normal extends up to the Canadian border is a little concerning in the Mid Atlantic. Maybe not so much New England.

La Nina (general) is a colder composite for you. Here are anti-Strong El Nino's: The EC is probably a little warmer than that composite, as there is somewhat of a -NAO signal. I think all the 5 Winter's you pointed out were warm on the EC (doesn't mean La Nina is warm, it just means the automatic cold signal in the historical database has some -NAO/-AO influence). I would probably push that cold to the Upper Midwest and NW lately, especially for more west-based events.

I don't think 13-14 is a bad analog, but the probability that it was going extreme did start to come up in the Fall, when the N. Pacific ridge went Polar. We would need to follow that closely imo to see a similar Winter pattern. 5/6 Winter's lately have been +WPO.. chances are it is more neutral this Winter, and the 21-22 Winter where it was neutral is a decent analog, although the timing of things may be more mixed (We had such an extreme "new" Dec -PNA that Winter that it flipped to +PNA for January).

Am I reading that right, -2.88 PDO in August? And the last 4 months have all been below -2.88? Wow! The PDO has a really strong correlation with the N. Hemisphere H5 pattern Oct-Dec. If we see -EPO/-WPO it probably won't be until the Winter imo.

Weak is just a less amplified state of the same thing.. Moderate/Strong ONI's translate to a 100dm Pac ridge in the Winter, while Weak's have translated to a 50dm Pac ridge. Our historical composite is too limited to assume Weak Nina's are automatically cold.. I remember a lot of talk about this in the early 2000s when the historical composite was very cold.. but then yeah, 5/5 of the last Weak Nina's have been warm. "Weak" just means that other factors like the NAO/AO may have larger credence.

I think the cold on the West Coast is partially because we had such a cold trough on the East coast the last few weeks.. We do still need some level of mid latitude cooling in the mix, not just all +pna/-pna. The heat wave in the SW, US with record streaks of 100+ for Phoenix and Las Vegas will still translate to super warm somewhere as the Fall jet stream gets going. History shows that those conditions there in the Summer do lead to some +PNA conditions in the Wintertime, usually in December, but a lot of times raw temperatures in the SW, US do lead the Midwest and East Coast somewhere down the road.. I'd rather them be cold than warm.

Huge Omega block being modeled This fits the pattern that we've seen for the last 5 years

No problem. We've lost arctic ice on the Pacific side and since then they have had Wintertime High pressure in the PNA region, while ice has stayed on the Atlantic side, near Greenland, and we have seen more low pressures in this region in the Wintertime. @bluewave Can probably point you in a good direction with literature on the subject.

January NAO.. Will it be a -PNA October? Pretty good correlation here The rest of the year NAO correlates at 51-54% with the Winter NAO, but October is the only month of the year where the correlation is <50%. This is especially true in JFM, where it holds a 55% opposite correlation

I said the -NAO/-pna/+epo correlation started in 2013, but when I looked back at cold seasons following the super arctic ice melt in 2007-2012, it appears that correlation was true even back that far. More cold did make it to the surface in the eastern 2/3 of the CONUS though, as bluewave pointed out. That pattern has moderated a lot lately, although last January we saw a pretty good pattern break, having some -NAO-driven cold.

We are +0.50 right now for DJFM (with 0.54 sd, 50% chance DJFM NAO comes in -0.04 to +1.04). A little less positive than I expected. In May we had a negative reading, so the warm pool later in the year has only been a part of the total measurement.

In 08-09, we started to see N. Pacific High pressure hit record levels. That was the first time that really did it in satellite era. That feature has become very strong at times in recent years, even popping over +600dm in Dec 2021. Since the arctic sea ice is melting on the Pacific side, and holding near Greenland on the Atlantic side, I do think that makes some sense.. especially since when the extreme ice melt happened in 07-12, we started seeing that N. Pacific High pressure become more frequent. It's probably not perfectly linear, but I do think since that whole western side of the Arctic circle melts in the Summer, it would flex High pressure over the north Pacific Ocean.

That's a good point. I think the correlation is sea-level height, sometimes reflected by surface SSTs. May-Sept water temps in that region has a strong correlation to the Winter NAO.. right now a custom index I made is coming at about 0.70 (+0.54 SD chance we see DJFM NAO come in around +0.70). Also, October is the only month of the year where the NAO has an opposite correlation to the Winter.. I know we have a big -NAO showing up on models for the end of Sept, but I've never really checked to see if that October opposite correlation runs into late Sept. Right now, I would say it's likely that we have a +NAO Winter.

Yeah, seriously. It seems like when the arctic ice melt stops, these massive ridges blow up. This has been the trend for many years now..

Las Vegas and Phoenix having such a consistently hot Summer does correlate to +PNA conditions in December, and sometimes it carries past then.. will be interesting with a La Nina and strong -PDO, which suggest the opposite.

I do believe that weather derivatives trading does effect the weather.. I'm probably in the minority though. Does anyone know why, probably related to arctic sea ice, a -NAO would correlate with -pna/+epo and +NAO correlates somewhat with +pna/-epo, once the cold season comes about? Another thing is sea level height.. I've connected this with subsurface water temps, especially near the thermocline. We've had a classic +NAO pattern according to sea-level height since 2011, while H5 has sometimes featured anomalous ridging near Greenland.

I contest that it is something other than +AMO and CC for why the NAO has held this correlation since 2013. It might even have to do with Summer arctic ice melt, as Greenland has held its core, and the Pacific side has gone completely iceless.. The lowest Summer arctic ice melt was 2012, then the -NAO starts connecting with dual-ridging (either over N. America or -PNA) in 2013, and carries it from that point forward, even intensifying after 2017. We see an ice melt season that is almost #2 this year, then there is this big -NAO/-PNA pattern once the cold season starts progressing on the Northern Hemisphere. It's almost like a "stop" is in place, and there is dual-ridging around Greenland at other times of the year (if someone has a more scientific reason, come forth).