bluewave

The even bigger question is are we a least starting to see a small shift in the PCC? Remember how the El Niño last year began with the record 1+2 warming so early on with that record late winter 2023 WWB which was so east based. This most recent WWB was shifted over to the EPAC also. Maybe this means that at least for shorter intervals the EPAC can have more influence at times than the WPAC warm pool and MJO 4-7 has had since December 2015. It’s also possible that the big jump in global temperatures since 2023 is related to changes in the EPAC near South America. But it’s probably too early to speculate on that until we get more data. https://www.nature.com/articles/s41467-024-52731-6 The eastern tropical Pacific has defied the global warming trend. There has been a debate about whether this observed trend is forced or natural (i.e., the Interdecadal Pacific Oscillation; IPO) and this study shows that there are two patterns, one that oscillates along with the IPO, and one that is emerging since the mid-1950s, herein called the Pacific Climate Change (PCC) pattern. As the tropical Pacific is known to be a climatic pacemaker, for (at least) the near-future this would mitigate global warming via ocean heat uptake and low-level cloud feedbacks. Instead, if the cyclic IPO dominates the recent cooling, we may expect a strong warming when it reverses.

It’s been a long time since we saw a 15 day swing in this direction for an early December forecast. But I will give the models credit for seeing the Aleutian Ridge shift north of the Aleutians. If the forecasts are still showing this type of shift from the recent years in early December, then the December 5th Euro seasonal update should look different from what it had on November 5th. New run Old run Dominant 500 mb pattern in December since 2015 with ridge south of Aleutians rather than north

This will probably be the first time in the last few years that a week 2 forecast trended colder instead of warmer. New run Old run

It’s possible that we are seeing the early stages of some type of 500 mb regime shift in the North Pacific. The ridge today in the Bering Sea has exceeded a +500 meter anomaly which is one of the strongest on record for this time of year. SST indices like the PDO are usually lagging indicators after the 500mb pattern gets stuck in place for a long enough period of time. For the 2020s so far the North Pacific Ridge has been anchored to the south of the Aleutians. So if the pattern can persist past the first week of December it’s possible that something significant shifted with this +AAM rise and WWB which caused the Nino 1+2s to warm off of South America. Near record 500 MB heights today Bering Sea 2020s mean ridge south of Aleutians

Would be an interesting question since the atmospheric 500 mb state now is more El Niño +PDO than La Niña with the high AAM pattern.

Even NOAA isn’t sure of what’s going on as this WWB and ENSO warming wasn’t forecast by any of the models along with the sudden jump in global temperatures starting back in 2023. https://www.newscientist.com/article/2452742-the-mystery-of-the-missing-la-nina-continues-and-we-dont-know-why/#:~:text=While sea surface temperatures in,by the end of November. An expected shift to cool La Niña conditions in the Pacific Ocean has been delayed again. Forecasters now project only a weak event to emerge by the end of November, which is likely to limit the cooling influence of the climate pattern on global average temperatures. “I do not know why it has slowed down,” says Michelle L’Heureux at the US National Oceanic and Atmospheric Administration (NOAA). “If someone did, we might have been able to predict it.”

If we can hold that day 11 snapshot, then it would be a blend of December 2017 and 2009. It will be interesting to see how long we can sustain that pattern since the MJO indicator in October that I discussed was going for a mismatch in December like we saw in 2020, 2017, and 2010. But since this La Niña was weaker than those years it was uncertain how well it would work. The WWB and AAM rise and ENSO warming we just saw may have been related to the very amplified MJO 5 wave that we saw in October. Still too early to tell how long that day 10 pattern lasts but we should know one way or another by the first week of December. We’ll know at that point if the pattern has staying power or it switches back to something more Niña-like after week 1.

Yeah, the challenge is that many of these AMOC forecasts are based on models with proxies and not direct measurements. This recent study on the Florida current is actually measured and is maintaining its strength. Other studies on the cold blob in the North Atlantic suggest that it may be a function of more persistent +NAO patterns at times. They still don’t know if it’s caused by glacier melt with fresh water. It’s possible that it could be a function of both but how much each contributes is an unknown. When we look at some of the AMOC slowdown forecasts they resemble a +NAO pattern. Notice how the models show the record SSTs and warmth near the NW Atlantic and New England while the NAO area expands and cools. A more amplified version of what we have seen in recent years.

Sometimes those composites work and other times the JMA are more reliable. Many of the MeteoNetwork composites are lower sample size. I translated the site to show the color codes and the degree of reliability. MJO Tables - MeteoNetwork Medium-high reliability Medium-low reliability Low reliability Plotting not available due to lack of data I like the JMA since each composite is based on a big sample size from 60 to 100 dates. Sample size can often be an issue with MJO composites so you need to see which work better in real time and then try to extrapolate out where the MJO is going and whether it’s having a strong enough effect. This current pattern forecast for late November is more of a +AAM with blocking near the Aleutians and Baffin Island. So the MJO may still be running in the background but not dominating the pattern. We’ll have to wait until early December to determine whether the +AAM dominates or we get a warmer MJO 5-7 influence. Another possibility would be an odd combination of both almost like wave interference. https://ds.data.jma.go.jp/tcc/tcc/products/clisys/mjo/composite.html High AAM pattern for late November

You can see the EPS weeklies showing mixed influences between Nino-like and Nina-like elements. We will probably need at least another 10 days to know which becomes more dominant. Another possibility is that we get some type of interference pattern between the two but still too earky to know. https://charts.ecmwf.int/products/extended-anomaly-z500?base_time=202411190000&projection=opencharts_global&valid_time=202412020000

Another thing to watch may be a sting jet-like feature just south of the low.

This is probably the first time we had such an impressive November Nino temperature rise following a borderline super El Niño SSTs like last winter.

This looks like one of the strongest storm systems we have seen in the East this year near -4SD.

You can see the battle unfolding from run to run between how long to linger this current more Nino-like regime and how fast to bring back a more Niña-like background pattern.

The Gulf of Maine is near the warmest on record for this time of year. https://mco.umaine.edu/climate/gom_sst/

GMRI tracks this part of the Atlantic which has consistently been near the warmest on record in recent years. https://gmri.org/stories/gulf-of-maine-warming-update-summer-2024/

Top 5 warmest fall across the entire region.

It would be great if the new Euro extended delivers on the multiple rainfall chances right into early December.

Great to see the models coming in wetter. This will be one of the strongest upper lows in the East this time of year. Hopefully, the is the first step toward a much wetter pattern as we head into December.

From my observations it’s the 500mb patterns which lead the SST anomalies. All the various warm blobs which are marine heatwaves first start out with s strong 500 mb ridge sitting over the ocean surface. We can remember the 500 mb pattern shifting first in the summer of 2013 and it took over a year for the changes in the actual PDO to show up. Then around 2018 the 500 mb pattern began shift back to a -PDO atmospheric state and it took the ocean a while to respond. The 500mb heights have been rising across the planet leading to more of these marine heatwaves. But once a pattern becomes established in the tropics or subtropics, then there can be a feedback process between the ocean and atmosphere which reinforces the pattern. But it’s possible what we call the PDO may first originate in a warmer tropical region and trigger a 500mb wave train which produces the 500 mb PDO response first. Then the SST response comes later after the 500mb pattern persists long enough.

You are fortunate to be in an area where the record warm lakes staying open longer works to your advantage with all those cutter storm tracks we have seen.

We’ll see if the later runs can cool enough so RDU doesn’t break their latest first freeze record.

One of the long range model biases has been to underestimate the strength and influence of the Pacific Jet. This is why long range modeled colder patterns usually modify the closer in we get. None of the long range models from a few weeks ago were this strong with the Pacific Jet for the record breaking event next few days. Remember the previous 11-15 day forecast was much colder than the present 6-10 day forecast. New run Old run

The forecast issue going forward may be that the La Niña is so weak that we get a mix of Nino-like and Nina-like intervals. Kind of like a windshield wiper effect. So would be a challenge getting any sustained cold with since a strong Pacific Jet.

The 12z GFS took a step toward the more amplified and wetter models. New run UL and vort digging more into GA Old run