bluewave

Maybe such an extreme North Pacific storm in early January means that we are nearing the peak of this +EPO cycle. If this is the case, then we would get some improvement on the Pacific side by mid-January. That could be what the weeklies are trying to show.

The timing is right for a coastal system around the 4th. Each -AO drop going back to early December has featured one. The first was on December 5th and the 2nd on the 16th. But we need the closing off of the upper low and storm separation following the New Years storm to work out. As Walt mentioned , the spacing issues could result in a scraper track if the New Years storm suppresses it. Exact storm tracks for the models are a challenge beyond 3-5 days. We just saw how the whole evolution of the New Years storm changed several days ago.

We continue to set records for warmth and snow together. This was only the 6th year with a 10”+ snowstorm in NYC from December 1st to the 20th. But it was the first December with an average temperature this warm. The warm up after the 20th was also a first to reach 60°. 2020.....39.3°......61° 2009.....35.9°......55° 2003.....37.6°......54° 1960.....30.9°......49° 1948.....38.3°......57° 1916.....34.0°......42° Record warmth to some type of snowfall record is becoming more frequent in recent years. November 2020 was the warmest on record in NYC at 53.0°...5th earliest seasonal 10.0”+ snowfall of 10.5” in December January to March 2020 was the 2nd warmest on record in NYC at 42.4°...trace of snow on May 9th tied with 1977 for latest on record after 7th coldest winter at 28.3° February 2018 was the warmest on record around the area with a first 80° at Newark .....NYC warmest February at 42.0°....ISP snowiest March at 31.9” of snow February 2017 featured 62° on 2-8 at ISP and 14.3” of snow on the 9th...2nd warmest February in NYC at 41.6° January 2017 produced 6.3” on the 7th in NYC and rose to 66° on the 12th..the month finished +5.4 December 2015 was warmest on record with a +13.3...50.3° in December....greatest snowstorm on record in NYC during January of 27.5” January 2006 was the 4th warmest in NYC at 40.9° followed by the 2nd biggest snowstorm in February of 26.9”

Every single model has a different storm evolution and solution for the 3-4th. Probably because it’s coming so soon behind the New Year’s Day storm. In general, models don’t handle storm details very well beyond 3-5 days out. Unless we are dealing with the Euro and Hurricane Sandy.

I think our best shot would be the upper low closing off like the Euro and GFS v16. Then we would need just the right amount of spacing between the New Years storm so the low doesn’t get suppressed. A perfect thread the needle would start warm and then transition colder. It would have to go off without a hitch due to the warmth after the New Years storm.

Pretty consistent pattern with the North American snow cover since October. Notice the big drops following the spikes back in October and mid-December. This tells us that it’s been a struggle to maintain the cold for more than brief periods.

If the past is any guide, then NYC may have to wait until later January or February for its next 6”+ snowstorm. There have been 9 years with a 6”+ event in NYC between December 1st and the 20th since 1930. The good news is that all of the 9 years did get at least one follow up warning level event. We would have to go back to 1926-1927 for the most recent year with no further 6”+ events in the season. NYC December 6”+ snowstorms before the solstice in December and the date of the next event 12-20-09......2-10-10 12-05-03.....1-27-04 12-5-02.......2-17-03 12-19-95.......1-7-96 12-11-60........1-19-61 12-3-57..........2-15-58 12-19-48.......2-28-49 12-19-45........2-20-46 12-18-32........2-11-33

2017 was the only cold December out of the last 10. That’s what it took to produce my favorite first week of January snowstorm over the last 10 years. That was the famous 950mb benchmark blizzard on 1-4-18. Monthly Mean Avg Temperature for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Dec Departure Mean 40.6 +3.1 2020 40.0 ? 2019 38.3 +0.8 2018 40.1 +2.6 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

BGM may have experienced one of the quickest reductions in a 35”+ snow depth for the Northeast. It only took BGM 8 days to drop from 39” to 1”. The last time BGM had snow depth at 35” it lasted 16 days in March 1993. SNOW DEPTH RECORD SET AT BINGHAMTON NY... THE SNOW DEPTH THIS MORNING AT 7 AM WAS 39 INCHES. THE OLD RECORD WAS 35 INCHES ON MARCH 15 1993 AFTER A BLIZZARD. RECORDS HERE AT THE GREATER BINGHAMTON AIRPORT GO BACK TO 1951. 2020-12-17 22 15 18.5 -8.1 46 0 1.69 26.4 39 2020-12-18 22 8 15.0 -11.3 50 0 0.00 0.0 31 2020-12-19 24 3 13.5 -12.5 51 0 0.00 0.0 29 2020-12-20 31 21 26.0 0.2 39 0 0.14 1.8 26 2020-12-21 36 29 32.5 7.0 32 0 0.02 T 22 2020-12-22 34 27 30.5 5.3 34 0 0.01 0.1 22 2020-12-23 36 22 29.0 4.0 36 0 0.00 0.0 20 2020-12-24 50 34 42.0 17.2 23 0 1.55 0.0 19 2020-12-25 53 20 36.5 12.0 28 0 0.80 0.8 1 1993-03-15 21 0 10.5 -21.8 54 0 T T 35 1993-03-16 39 19 29.0 -3.6 36 0 0.00 0.0 32 1993-03-17 39 7 23.0 -10.0 42 0 0.21 1.0 26 1993-03-18 14 -3 5.5 -27.9 59 0 0.00 0.0 24 1993-03-19 31 -7 12.0 -21.7 53 0 0.00 0.0 24 1993-03-20 32 19 25.5 -8.6 39 0 0.04 0.7 20 1993-03-21 39 27 33.0 -1.5 32 0 0.28 3.9 25 1993-03-22 36 24 30.0 -4.9 35 0 T T 22 1993-03-23 37 18 27.5 -7.8 37 0 0.56 0.2 20 1993-03-24 40 32 36.0 0.3 29 0 0.10 0.0 18 1993-03-25 40 31 35.5 -0.6 29 0 T 0.0 16 1993-03-26 55 24 39.5 3.0 25 0 0.00 0.0 14 1993-03-27 58 30 44.0 7.1 21 0 0.00 0.0 12 1993-03-28 54 39 46.5 9.2 18 0 0.12 0.0 9 1993-03-29 47 42 44.5 6.8 20 0 0.40 0.0 6 1993-03-30 52 36 44.0 5.9 21 0 0.01 0.0 5 1993-03-31 60 31 45.5 6.9 19 0 0.01 0.0 3

Our warm up around the solstice has become the new normal for us. This is the first 10 consecutive years to reach 55° or warmer in NYC. It pushed the NYC December average temperature so far to 40° and +1.7. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Ending Date Highest Max Temperature Dec 18 to Dec 25 Missing Count 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 2009-12-25 39 0

Ridiculously strong 6SD+ southerly jet streak with the record warmth pushing into Canada.

The best SSW outcomes for us were when the Pacific has cooperated. You can run down the list and see which years worked for us. As has been the case in recent years, it will probably come down to how the Pacific responds. Full list of events https://csl.noaa.gov/groups/csl8/sswcompendium/majorevents.html

POU sets a new December 25th record high of 65°. This makes it the greatest 140 hr temperature rise there for December. The low between hours on the 19th was -3°missing the record low by 1°. So this would make a 68° temperature rise. The chart below only does hourly readings. https://mesonet.agron.iastate.edu/plotting/auto/?_wait=no&q=169&network=NY_ASOS&zstation=POU&hours=140&month=dec&dir=warm&dpi=100&_fmt=png RECORD EVENT REPORT NATIONAL WEATHER SERVICE ALBANY NY 835 AM EST FRI DEC 25 2020 ...RECORD HIGH TEMPERATURE SET AT POUGHKEEPSIE NY... A RECORD HIGH TEMPERATURE OF 65 WAS SET AT POUGHKEEPSIE NY TODAY AT 400 AM. THIS BREAKS THE OLD RECORD OF 63 SET IN 1964. CLIMATE REPORT NATIONAL WEATHER SERVICE ALBANY NY 435 PM EST SAT DEC 19 2020 ................................... ...THE POUGHKEEPSIE NY CLIMATE SUMMARY FOR DECEMBER 19 2020... VALID TODAY AS OF 0400 PM LOCAL TIME. CLIMATE NORMAL PERIOD: 1981 TO 2010 CLIMATE RECORD PERIOD: 1931 TO 2020 WEATHER ITEM OBSERVED TIME RECORD YEAR NORMAL DEPARTURE LAST VALUE (LST) VALUE VALUE FROM YEAR NORMAL ................................................................... TEMPERATURE (F) TODAY MAXIMUM 26 3:08 PM 60 1931 39 -13 25 MINIMUM -3 7:39 AM -4 1989 21 -24 14 AVERAGE 12 30 -18 20

Yeah, the Pacific Jet will continue to dominate into late December. It will be interesting to see if the SSW verifies. If it does, then we’ll have to wait and see if it benefits Eurasia or North America.

First December for NYC with 10”+ of snow and a 60°Christmas. It was also the first 7 year period with 3 years reaching 60° or warmer on Christmas. Data for December 25 - NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Date Max Temperature Min Temperature Precipitation Dec Snowfall 2015-12-25 66 57 0.01 T 1982-12-25 64 41 0.02 3.0 1889-12-25 64 43 0.00 6.0 2014-12-25 62 44 0.09 1.0 1940-12-25 62 38 0.00 3.0 1979-12-25 61 50 0.87 3.5 2020-12-25 61 10.5 1964-12-25 60 49 T 3.1

Yeah, the Wantagh mesonet gusted to 53 mph on the South Shore at 58°. Further north in Westchester the Somers station gusted to 71mph while at 61°.

The strongest gusts in the 63 to 78 mph range were in the areas that got to 60° or above. https://mesonet.agron.iastate.edu/wx/afos/p.php?pil=PNSOKX&e=202012251003 Greenwich 71 MPH 1131 PM 12/24 CWOP Stamford 70 MPH 0328 AM 12/25 CWOP Teterboro Airport 67 MPH 0151 AM 12/25 ASOS NYC/La Guardia 63 MPH 0251 AM 12/25 ASOS Jackson Heights 67 MPH 0152 AM 12/25 CWOP Eatons Neck 76 MPH 1248 AM 12/25 WXFLOW Brookhaven 64 MPH 0445 AM 12/25 CWOP Somers 71 MPH 0330 AM 12/25 NYSM Robbins Reef, NJ 78 MPH 0242 AM 12/25 NOS-PORTS

The Queens College sensor at 179 ft gusting to 46 mph. LaGuardia Arpt CLOUDY 58 49 72 S17G29 29.98F Queens College N/A 57 52 82 S22G46 N/A

It helped having the 4 coldest days of the month follow the snowstorm.

The oddity this month for NYC is how mild it has been for a December with a 10”+ snowstorm. Most other Decembers were much colder. But warm and snowy has been a new theme that has emerged since the mid 2000’s. 2020...39.3...so far 2010...32.8 2009...35.9 2003...37.6 2000...31.1 1960...30.9 1948...38.3 1947...34.0 1933....32.7 1916....34.0 1912....39.3 1872....26.7

Yeah, that is a lot of water ready to be released from the snowpack. It should be noted, that while snow depth has markedly decreased across the area since the big winter storm last week; it has really only settled and compressed. Most of the water content is still there; for example at NWS Binghamton the depth is now only 19 inches - now under half what it was - yet it contains slightly more than 3 inches of water. There is a lot of water ready to be released from the dense snowpack, especially for the Susquehanna Basin and Upper Delaware Basin.

The BGM AFD really highlights how extreme an event this is. 645 AM Update... Just adding an extra word to stress, that this is no ordinary Flood Watch; flooding is not just possible but indeed expected, and it will likely be quite significant for much of the area - both the initial flash flood/small stream phase late today into tonight, and the main stem river phase late tonight through Friday. Some of the signals that we look for in the models for flood potential, such as mean integrated water vapor transport, precipitable water, and southerly component of 850 mb winds; are either off-the-charts or nearly so for this time of year. This is a rare set up. This would be a problem even in the absence of snow cover, but unfortunately was also have plenty of water that will be released from deep snowpack in the warm moist and windy conditions later today through tonight - especially the Susquehanna and Upper Delaware basins. Anyone living in a flood- prone area should have a plan and know what to do in the event high water threatens.

The south based blocking has been a theme this month. Notice the warmer than normal temperatures pushing down into the Northeast. This may be related to the record SSTs over the NW Atlantic and cold pool south of Iceland.

We only needed one storm this month for many areas to get to above normal snowfall. That was when the +PNA combined with the -AO-NAO. It really came down to that supercharged 50/50 low we got. Otherwise, the tucked in storm on the 16-17th would have been a warmer event. As it was my area only got 4” of snow due to the WAA aloft and quick flip to sleet. The month will end milder than models were expecting just several days ago. You mentioned the trade wind surge a few days ago. That may be related to why we are getting the Niña ridge showing up north of Hawaii. But this is still occurring with other more Niño-like features. We would definitely need more help from the PNA in January to counter the +EPO and fast Pacific Jet. But those short term details usually don’t show up on the longer range forecasts. Just a little +PNA can go a long way with -AO -NAO. Slight Niña Ridge poking up north of Hawaii allowing more of a trough out West

That’s why we have to wait for the individual short waves. We will definitely need help from the PNA with such a strong PAC Jet and +EPO. But models won’t show those fine details until we get within about a week of the actual forecast period.