bluewave

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

This was the strongest WWB event in the EPAC during the month of November following such a strong El Niño winter. Reminds me a bit of the unusually strong EPAC WWB activity we saw that kicked off the El Niño in the winter and spring of 2023. This isn’t something we see during El Niño to La Niña transitions.

My guess is that the more Nino-like look to the 500 mb pattern this week is a result of the unusual EPAC WWB we just experienced. The million dollar question is how long this pattern lasts? We need it to continue for more than just a few weeks. Ridge axis shift from 30N to 60N