bluewave

The latest extended EPS continues the warm -PNA +AO pattern into late December. It develops a west based EPO ridge near Alaska during late December. But still has a SE Ridge here due to the -PNA and +AO. So Western Canada gets much colder. The MJO eventually gets over to 7, but it’s forecast to destructively interfere with the La Niña. So that may be why it takes longer to build the ridge into Alaska. We would probably need a cleaner MJO 7 response to start pushing the gradient closer to the Northeast during the last week of December. https://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjoupdate.pdf • A Pacific MJO event is likely to destructively interfere with La Niña, and there remains uncertainty as to whether the MJO will maintain an organized structure, as evidenced by large ensemble spread in the RMM forecasts through mid-December. Dec 6-13 Dec 13-20 Dec 20-27

Winter version of the Ambrose Jet. Cooler conditions and winds gusting near 35 mph along the South Shore. Mid-60s at the usual spots in NJ. Kennedy Intl PTSUNNY 53 51 93 S29G37 29.74F FOG Breezy Point N/A 52 N/A N/A S25G35 N/A Newark/Liberty PTSUNNY 65 52 62 S15G29 29.69F Teterboro MOSUNNY 62 53 72 S17G25 29.68F Caldwell LGT RAIN 64 52 64 VRB7 29.69F Somerville PTSUNNY 64 54 69 S8 29.66F Linden PTSUNNY 65 50 59 SW10G21 29.69F Perth Amboy N/A 63 N/A N/A S18G25 N/A

Going warm has been the winning forecast for 9 out of the last 10 Decembers. Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Dec Click column heading to sort ascending, click again to sort descending. Year Mean Avg Temperature Departure 2020 39.2 +1.7 2019 38.3 +0.8 2018 40.1 +2.5 2017 35.0 -2.5 2016 38.3 +0.8 2015 50.8 +13.3 2014 40.5 +3.0 2013 38.5 +1.0 2012 41.5 +4.0 2011 43.3 +5.8

That’s not how it works. December has been warming at close to 1° per decade over the last 40 years. We started out closer to 35° and now are approaching 40° in the averaged means for our whole climate division. So by mid-century, averages closer to 45° will become the norm. The warming baseline makes it easier for the more extreme years like 2015 to occur. We saw this in February 2018 with our first 80. So one of these Decembers in the future will eventually produce an 80° reading also.

While December 2015 has been the most extreme expression of the US December warming trend, the composite of the other years since 2011 shows the same pattern.

December has been the warmest winter departure month over the last decade. It’s no surprise that the models have corrected so much warmer in recent days. Summer has been extended into fall and fall into early winter.

You know it’s a very warm December pattern when Long Island is approaching 60° early in the morning. CITY SKY/WX TMP DP RH WIND PRES REMARKS Jones Beach N/A 57 N/A N/A S13G18 N/A Wantagh N/A 57 55 94 S10 N/A Hempstead NOT AVBL Matinecock Pt N/A 52 N/A N/A N1 N/A Farmingdale CLOUDY 57 55 93 S15G24 29.94F MacArthur/ISP CLOUDY 57 56 96 S14 29.94F Stony Brook N/A 55 54 94 S7 N/A Shirley MOCLDY 57 54 89 SE14G23 29.97F Mt Sinai Harb N/A 55 N/A N/A S10 N/A Westhampton CLOUDY 55 53 93 SE14G21 29.98F East Hampton CLOUDY 53 51 94 SE15G23 29.98F Southold N/A 54 52 94 S18 N/A Montauk N/A 54 52 93 S12G21 30.02F

The latest Euro monthly has a low heating bill special for the US in December.

The CMC came south from yesterday due to a faster Pacific Jet flattening the ridge near California. New run Old run

That’s why many people were disappointed when the NCEP chose the FV3 core over the MPAS. https://blogs.agu.org/wildwildscience/2016/07/28/noaa-makes-decision-new-global-weather-model-controversy-likely/

The NAM looks like it could be a possibility with the fast flow putting us in the NW edge of the precipitation shield. This may mean that the recent Euro fix worked for East Coast storms. Those tucked in low solutions from the GFS don’t really match the pattern.

The record storm near Japan and the typhoon are probably a big part of why the current MJO phase 6 pattern is getting disrupted. A -PNA is the opposite of what we would expect from a MJO 6 La Niña December composite. The near record Aleutians Ridge and deep -PNA trough for mid-December will probably take time to shift.

Our actual pattern in late November was a perfect match for a November La Niña phase 5. We had the classic +PNA and -NAO pattern. But the block in the North Atlantic was more south based probably due to the record SSTs off the East Coast.

The last few weeks have been classic MJO phase 5. The strongest VP anomalies were too far west to be in the phase 6 region. The wave break a few days ago disrupted the whole pattern. Notice the big VP anomalies jump into Eastern Siberia. That’s probably a part of what all the models have a big -PNA in mid-December going against the Phase 6 +PNA for December.

The last few weeks have been a November phase 5 for a La Niña. We are just going into December phase 6 right now. The mid-December -PNA that the models have been adverting is the opposite of what to expect from a La Niña phase 6 in December. My guess is that losing the +PNA is related to the big West PAC wave break amplifying the Aleutians Ridge . That being said, it’s possible that the MJO can start having a bigger influence later in December. It could take another wave break to shake things up again.

A thread the needle SWFE has been our storm track of choice when the general pattern was challenging. The models seem struggle even more when a storm follows another one by only a few days. But I don’t really trust individual model forecasts for coastals until we get under 72 hrs.

The only trends that seem to matter for us are the ones that occur under 72 hrs. It would be great if we had a model that could get a 96-120 hr coastal storm track correct. Funny how models usually can get cutters right from a week out.

Another indicator that the pattern driving the fall record +EPO and current -PNA is on steroids.

Here in SW Suffolk about 75% of the trees have lost their leaves. But there are still a few trees that are still fully leafed out in brilliant colors. This may be some of the best color that we have seen in early December. The current photos coming in from NYC are just gorgeous.

It doesn’t look like the current MJO phase 6 is having much influence on the pattern. A MJO phase 6 during a La Niña is a strong +PNA. Currently getting the opposite now with a strong -PNA. We can only hope that if it goes into 7 that we get something resembling an actual phase 7 later in December.

We will need a SSW in January. There were only 3 La Niña Decembers with a strong -PNA and +AO. while 08-09 and 84-85 had SSWs in January, 71-72 didn’t. That being said, 3 years is a very small sample size and our climate has warmed quite a bit since then. But we would be happy to get some blocking to push back against the Pacific Jet for snow chances. https://csl.noaa.gov/groups/csl8/sswcompendium/majorevents.html

It seems like the pattern forcing this near record -PDO is having a greater influence than just the La Niña alone. The -PDO is being driven by the extreme vortex in the Northeast Pacific. This caused a record +EPO in the fall. The vortex is next forecast to move to a very strong -PNA position. Unfortunately, this is combining with a very +AO pattern. The main question is what is forcing the -PDO instead of recent years with a more +PDO La Niña ? All the guidance has -PNA +AO until further notice

They have a site called confluence that reviews how the Euro did with some individual East Coast storms. The case below was for the January 2016 blizzard. It had too much storm suppression keeping the heaviest snows south of NYC. That was the one of the biggest NAM wins that we ever saw. https://confluence.ecmwf.int/display/FCST/201601+-+Snowstorm+-+US+east+coast 5. Good and bad aspects of the forecasts for the event Early signal (from Sunday 17 Jan 00z) and very consistent forecasts Too low accumulation over NYC Question about snow density for the case

This will be the first test of the newly upgraded Euro with a coastal storm in the winter. It had been having suppression issues with coastal storms in recent years. So if the models like the GFS and CMC are right about a track closer to our area, then they weren’t able to address this issue on the upgrade. But if the CMC and GFS go south then we’ll know the issue was fixed. While the Euro has been the top scoring global model in recent years, I have never seen any official statistics for East Coast storm track performance. Maybe the model is tuned for performance in Europe? Even though the Euro has struggled with East Coast storm tracks in recent years, it still does good with the EPS 500 mb teleconnection patterns. My only critique is that it can be too weak with ridges along the East Coast and show too much ridging near Alaska. This was the case recently with it having too weak a +EPO and too slow a Pacific Jet. It also seems like the GFS was a little faster to show the Pacific Jet flattening the Western Ridge and big -PNA drop.

The warmer pattern has actually moved up in time vs what the models were showing at the end of November. Both the 6-10 day forecasts and 11-15 were too cold. The warmer start to December so far and the warm up ahead of the cutter on Monday wasn’t even forecast. New 1-5 vs old 6-10 New 6-10 vs old 11-15