bluewave

It’s an interesting conversation about the right temperatures leading up to a 6”+ or 12”+ event in NYC in our warmer climate. The key seems to be what the low temperatures are doing in the days before or during the event. While we can have highs in the 50s or even 60s right before the storm, we need at least a few days with lows getting into at least the mid 20s or colder. I think getting the lows into at least the mid 20s before or during storm time tells us there is cold enough air supply nearby to be drawn into the developing low. This is when we get favorable storm day teleconnections and storm track and evolution. I added some of our milder events surrounding storms in recent years for illustration purposes in NYC. The cold for the December storm came with the arrival of the event. 2017-02-01 47 33 40.0 6.8 25 0 0.00 0.0 T 2017-02-02 45 32 38.5 5.2 26 0 0.00 0.0 0 2017-02-03 33 26 29.5 -3.9 35 0 0.00 0.0 0 2017-02-04 34 22 28.0 -5.5 37 0 0.00 0.0 0 2017-02-05 43 31 37.0 3.3 28 0 0.00 0.0 0 2017-02-06 49 36 42.5 8.7 22 0 0.00 0.0 0 2017-02-07 42 36 39.0 5.1 26 0 0.27 0.0 0 2017-02-08 62 38 50.0 15.9 15 0 0.03 0.0 0 2017-02-09 44 19 31.5 -2.7 33 0 1.16 9.4 2 2017-02-10 32 19 25.5 -8.9 39 0 T T 8 2017-02-11 48 30 39.0 4.5 26 0 0.00 0.0 5 2017-02-12 40 30 35.0 0.3 30 0 0.46 T 2 2017-01-04 52 34 43.0 10.0 22 0 0.00 0.0 0 2017-01-05 34 27 30.5 -2.4 34 0 0.00 0.0 0 2017-01-06 33 25 29.0 -3.8 36 0 0.05 1.2 1 2017-01-07 26 20 23.0 -9.7 42 0 0.32 5.1 T 2017-01-08 25 16 20.5 -12.1 44 0 0.00 0.0 4 2017-01-09 23 14 18.5 -14.0 46 0 0.00 0.0 3 2017-01-10 46 21 33.5 1.1 31 0 0.00 0.0 3 2017-01-11 52 42 47.0 14.6 18 0 0.52 0.0 0 2017-01-12 66 47 56.5 24.2 8 0 0.05 0.0 0 2017-01-13 62 32 47.0 14.7 18 0 0.00 0.0 0 2016-01-10 59 40 49.5 17.1 15 0 1.80 0.0 0 2016-01-11 40 26 33.0 0.6 32 0 0.00 0.0 0 2016-01-12 44 25 34.5 2.2 30 0 0.00 T 0 2016-01-13 30 22 26.0 -6.3 39 0 0.00 0.0 0 2016-01-14 38 22 30.0 -2.3 35 0 0.00 T 0 2016-01-15 51 34 42.5 10.2 22 0 T 0.0 0 2016-01-16 52 42 47.0 14.8 18 0 0.24 0.0 0 2016-01-17 42 30 36.0 3.8 29 0 0.05 0.4 0 2016-01-18 31 18 24.5 -7.8 40 0 T T T 2016-01-19 28 16 22.0 -10.3 43 0 0.00 0.0 T 2016-01-20 37 27 32.0 -0.3 33 0 0.00 0.0 T 2016-01-21 36 26 31.0 -1.3 34 0 0.00 0.0 0 2016-01-22 30 21 25.5 -6.9 39 0 0.01 0.2 0 2016-01-23 27 24 25.5 -6.9 39 0 2.31 27.3 6 2016-01-24 35 20 27.5 -5.0 37 0 T T 22 2018-03-17 48 27 37.5 -5.1 27 0 0.00 0.0 0 2018-03-18 43 28 35.5 -7.4 29 0 0.00 0.0 0 2018-03-19 47 33 40.0 -3.2 25 0 0.00 0.0 0 2018-03-20 39 30 34.5 -9.1 30 0 T 0.0 0 2018-03-21 39 31 35.0 -8.9 30 0 0.99 8.2 0 2018-03-22 50 32 41.0 -3.2 24 0 0.06 0.2 8 2020-12-13 62 47 54.5 16.3 10 0 0.00 0.0 0 2020-12-14 47 35 41.0 3.1 24 0 0.26 T 0 2020-12-15 39 30 34.5 -3.0 30 0 0.00 0.0 0 2020-12-16 31 24 27.5 -9.7 37 0 0.86 6.5 0 2020-12-17 33 24 28.5 -8.4 36 0 0.66 4.0 9

We will have to deal with a very mild start to January before we can get to the retrograding -AO block and Pacific improvement by mid-January. Looks like we are close to a new all-time lowest pressure near Alaska. So my guess is that the early part of January will represent the peak +EPO. The hope is that the -AO retrogression will allow the EPO to back off enough for more ridging to build over Western North America and more +PNA. Every model group shows this scenario so it looks like it could really happen. So we’ll just have to watch for the 11-15 means to make it to day 7 for verification and forecast purposes.

Something similar happened after the February 2018 SSW. The SPV wound up in Asia. But due to the improvement on the Pacific side, we got the record snows. So the key going forward will be the ability to get a successful NAO retrogression and Pacific improvement.

Yeah, looks just like the December pattern this year. https://advances.sciencemag.org/content/4/7/eaat6025 Previous studies have extensively investigated the impact of Arctic sea ice anomalies on the midlatitude circulation and associated surface climate in winter. However, there is an ongoing scientific debate regarding whether and how sea ice retreat results in the observed cold anomaly over the adjacent continents. We present a robust “cold Siberia” pattern in the winter following sea ice loss over the Barents-Kara seas in late autumn in an advanced atmospheric general circulation model, with a well-resolved stratosphere. Additional targeted experiments reveal that the stratospheric response to sea ice forcing is crucial in the development of cold conditions over Siberia, indicating the dominant role of the stratospheric pathway compared with the direct response within the troposphere. In particular, the downward influence of the stratospheric circulation anomaly significantly intensifies the ridge near the Ural Mountains and the trough over East Asia. The persistently intensified ridge and trough favor more frequent cold air outbreaks and colder winters over Siberia. This finding has important implications for improving seasonal climate prediction of midlatitude cold events. The results also suggest that the model performance in representing the stratosphere-troposphere coupling could be an important source of the discrepancy between recent studies.

The EPS gradually transitions the main NH blocking from the Kara-Barents regions of Europe over to the Davis Strait by the 2nd week of January. December featured a very strong block in this region and an intense East Asian Jet which carved out a deep trough over the North Pacific. This lead to the strong Pacific influence that we are experiencing from late December into early January. The shift in heights could allow the North Pacific Jet to buckle and allow a retrogression of the Greenland block. This would represent some improvement by mid-January in the EPO. Sometimes that’s all we need to get the ball rolling toward a MECS regime by mid to late January.

Several times since 1995 NYC has had a snowy December following an extremely high ACE hurricane season. Accumulated Cyclone Energy - Atlantic hide Season ACE TS HU MH NYC Dec Snowfall 2020 180.1015 30 13 6 10.5 2019 132.2025 18 6 3 2.5 2018 132.5825 15 8 2 T 2017 224.8775 17 10 6 7.7 2016 141.2525 15 7 4 3.2 2015 62.685 11 4 2 T 2014 66.725 8 6 2 1 2013 36.12 14 2 0 8.6 2012 132.6325 19 10 2 0.4 2011 126.3025 19 7 4 0 2010 165.4825 19 12 5 20.1 2009 52.58 9 3 2 12.4 2008 145.7175 16 8 5 6.0 2007 73.885 15 6 2 2.9 2006 78.535 10 5 2 0 2005 250.1275 28 15 7 9.7 2004 226.88 15 9 6 3.0 2003 176.84 16 7 3 19.8 2002 67.9925 12 4 2 11.0 2001 110.32 15 9 4 T 2000 119.1425 15 8 3 13.4 1999 176.5275 12 8 5 T 1998 181.7675 14 10 3 2.0 1997 40.9275 8 3 1 T 1996 166.1825 13 9 6 T 1995 227.1025 19 11 5 11.5

It will be interesting to see if the Bering Sea low can break the all-time record. The last January with a NW PAC low with a 932 mb pressure or lower was 2013. That also occurred around the time of a SSW. It will be interesting to see if the weeklies are correct about the -NAO retrogression and EPO improvement by mid-January. https://www.wunderground.com/blog/weatherhistorian/bering-sea-superstorm-bottoms-out-at-924-mb.html https://csl.noaa.gov/groups/csl8/sswcompendium/majorevents.html JAN 2013 7-Jan-13 6-Jan-13 7-Jan-13 6-Jan-13 N E

Makes sense that a really amped up solution would be warm at the coast with such an unfavorable Pacific. The closed low went north of us this run. We needed a perfect thread the needle UL track and storm spacing to get at least a change to snow after such a mild start to the storm.

Looks like the 12z UKMET is trying to show something like the 0z Euro. But it isn’t easy to see the exact details with these low resolution maps. https://www.meteociel.fr/modeles/ukmo2.php?carte=1021&ech=72&nh=1&archive=0

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°.