bluewave

Chances are we see a moderation of the pattern by mid to late December since we haven’t had a cold start to finish December with every week colder than average since 2010 around NYC.

Very impressive Nino 1+2 warming as they were able to surpass a warm minimum record in Peru from the super El Niño in 97-98. With sea temperatures unusually high off our coast, minimum temperatures are responding to this warming. The airport at #Lima - #Callao saw an overnight minimum of 19.2°C. This is the highest value for the date since the great #Niño of 1997-8. We are just 4 weeks away from the start of summer and it will be a question of the struggle between the cold and warm Kelvin waves with the winds blowing at low altitudes; whether the warming survives or not. If it survives a warmer than usual summer, that's something to bet on.

It will be an interesting test of what occurs during the 2nd week of December. On one hand the EPS weeklies back in 13-14 and 14-15 were continuously trying to break the ABNA pattern down beyond 15 days. The models kept pushing the pattern moderation back in time the closer in we got. But the Pacific Jet from Japan to the east was much weaker those winters. The model forecasts have some pretty impressive jet extensions forecast in early December near Japan. So it will be interesting to see if they can sustain the pattern or cause it to relax.

My guess is that the December forecast will be determined by jet extension and retraction dynamics. Sometimes these big WPAC jet extensions can sustain an existing pattern like we are seeing in the forecast for the first week of December. So it would cause the pattern to reload for the 2nd week. But the wild card with all these jet extensions is that they can also reverse a pattern. So the thing to watch in later runs is whether one of the jet extensions can cause the ridge out West to drift into the East by mid-December.

Thats OK for areas further north in the Upper Midwest into Canada closer to where the Arctic highs are generated. But those air masses moderate quickly in early December coming south with the lower snow cover.The Great Lakes are also near record warm after the warmest fall on record for many areas. So while we will see a colder start to December , the air masses will moderate coming east of the Great Lakes. Cold air moderating coming east of the Lakes with coldest departures going to the south

This October into early December MJO forecast is similar to 2020 which I mentioned with the high amplitude MJO 5 both Octobers and weaker MJO 5 in December before going into the circle.

It will be interesting to see if we can get another round of Nino 1+2 warming in early December if a follow up WWB verifies near 120W like the GFS has.

The 2nd half of December has been warming at a faster rate than the 1st half around the Northeast spots like NYC over the last 30 years. Every year since 2011 there has been a warm up between the 17th and 25th going over 55°. So it would be quite an accomplishment if we got a relaxation of this pattern for even one year. December 17 to 25 maximum temperature NYC over 55° every year since 2011 Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. 2023-12-25 62 0 2022-12-25 58 0 2021-12-25 60 0 2020-12-25 61 0 2019-12-25 57 0 2018-12-25 61 0 2017-12-25 55 0 2016-12-25 58 0 2015-12-25 72 0 2014-12-25 62 0 2013-12-25 71 0 2012-12-25 56 0 2011-12-25 62 0 2010-12-25 40 0

One thing to note for the first week of December is that the 850 mb temperature departures are forecast to be colder than the 2m since the Northern Hemisphere snow cover is still near record lows and will need some time to catch up.

Best November snowfall in those areas since 2018 and 2014. Monthly Data for November 2018 for Sussex County, NJ Click column heading to sort ascending, click again to sort descending. ANDOVER TWP 1.7 W CoCoRaHS 8.5 CANISTEAR RESERVOIR COOP 0.0 FRANKLIN 1.3 NE CoCoRaHS 0.0 HARDYSTON TWP 3.2 SE CoCoRaHS 7.6 HIGHLAND LAKES 1SW COOP 10.9 MONTAGUE TWP 2.7 WNW CoCoRaHS 8.5 STILLWATER TWP 1.0 WSW CoCoRaHS T SUSSEX 1 NW COOP 9.0 VERNON TWP 1.7 N CoCoRaHS 8.8 WANTAGE TWP 1.6 SE CoCoRaHS 0.0 Monthly Data for November 2014 for Sussex County, NJ Click column heading to sort ascending, click again to sort descending. ANDOVER TWP 1.7 W CoCoRaHS 6.5 CANISTEAR RESERVOIR COOP 0.0 HARDYSTON TWP 3.2 SE CoCoRaHS 10.5 MONTAGUE TWP 2.7 WNW CoCoRaHS 8.9 SPARTA TWP 4.0 SW CoCoRaHS 7.6 SUSSEX 1 NW COOP 6.7 VERNON TWP 1.7 N CoCoRaHS 10.5 WANTAGE TWP 1.5 SE CoCoRaHS 5.4

We need a little more rain by the end of the month in order to avoid the driest fall on record. Time Series Summary for ISLIP-LI MACARTHUR AP, NY - Sep through Nov Click column heading to sort ascending, click again to sort descending. 1 2024 2.84 9 2 1965 3.31 0 3 2001 4.02 0 4 2013 4.86 0 5 1973 5.38 0 Time Series Summary for NY CITY CENTRAL PARK, NY - Sep through Nov Click column heading to sort ascending, click again to sort descending. 1 2024 3.34 9 2 1908 4.00 0 3 1909 4.67 0 4 1881 4.93 0 5 1931 4.97 0 Time Series Summary for NEWARK LIBERTY INTL AP, NJ - Sep through Nov Click column heading to sort ascending, click again to sort descending. 1 2024 2.51 9 2 1931 4.21 0 3 1964 4.93 0 4 2013 5.02 0 5 1941 5.04 0

I recently pointed out how unusual that WWB was in the EPAC was. Thanks to Anthony for pointing out how anomalous it was. Strongest November WWB since 97-98 super El Niño at 120W. This extreme event is part of why the atmosphere has shifted to such a strong +AAM and more Nino-like pattern. https://bsky.app/profile/antmasiello.bsky.social The westerly wind burst earlier in the month was pretty strong and is worth a further dive into the data/better analysis. Quick glance at Reanalysis daily data in Nov, for the equatorial 850mb zonal wind anomaly at 120°W since 1950, shows it was the strongest since the 1997 and 1998 November events.

It’s looking more like we some type of mismatch pattern at least for the first 2 weeks of December where the entire Pacific pattern goes in the opposite direction of La Niña due to the recent +AAM spike and Nino 1+2 warming. November 5th Euro forecast for December with a stock La Niña -PDO composite New run more of a mismatch pattern which I discussed back in October with the MJO following highly amplified October 2020, 2017 pattern and less influence in December

The loop back in from the Atlantic is like a much warmer version of 2-26-10.

Could see some heavy convection tonight over LI and CT with the low backing in off the Atlantic which would enhance the much needed rainfall.

The thing to watch is where the storm track sets up. While the models ave been correcting stronger with the ridge over the Bering Sea into the first week of December, they still have a robust MJO wave running through 4-6. So even if it’s not the dominant factor it can still influence the storm tracks. If it’s strong enough the lows could run close to or just inland from I-95. Then the cold we see on the week 2 means could come in behind any lows rather than in front of them. If the storm tracks are still too warm for the coast, then will know the MJO is still exerting some influence. Should the storm tracks slide east then we’ll know the block near Alaska won out. It will be interesting to see how things go.

The metric we all want to see from one of those skill charts is how the models rank with storm system forecasts in the Eastern US. But they don’t keep track of that data as far as I can tell. So while the broad skill scores have value, they may not translate very well into which model has the most accurate storm tracks in our area. It could just be that the interaction of continental air masses with the multiple mountain ranges and the Gulf Stream causes long range storm track skill to vary from the those average 500 mb charts.

The seasonal models like the Euro can be pretty good during the first month they are initialized in. But the 2nd and 3rd months can be very different from the forecasts. This is why the Euro December 5th update for the month of December is usually more reliable than the one issued on November 5th. Go back and look at how much variation there has been from the seasonal model forecasts issued in November.

Another theory is that the recent record warming of the EPAC near South America in early 2023 was strong enough to shift the PCC leading to the faster rate of warming last few years. 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 https://theweek.com/news/environment/961878/cold-tongue-pacific-ocean-cool-patch-climate-change This isn’t just an “academic puzzle”, New Scientist said. In fact, according to Pedro DiNezio, at the University of Colorado Boulder, it is “the most important unanswered question in climate science”. Not knowing what is causing it “means we also don’t know when it will stop, or whether it will suddenly flip over into warming”, New Scientist added. This has huge worldwide implications and “could determine whether California is gripped by permanent drought or Australia by ever-deadlier wildfires” as well as “the intensity of monsoon season in India and the chances of famine in the Horn of Africa”. More profoundly still, “it could even alter the extent of climate change globally”, the site said, “by tweaking how sensitive Earth’s atmosphere is to rising greenhouse gas emissions”.

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.”