bluewave

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

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

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

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.

Clash of the Titans pattern on the EPS 11-15 day mean. Firehose Pacific Jet vs one of the strongest -NAO -AO blocks that we have seen in early January. We need to get a nice retrogression of the Greenland block back toward the PNA region. A small +PNA rise can go a long way with a North Atlantic look like that. So some interesting tracking coming up in January when the individual short waves come into better focus.

South Florida and New England will have similar temperatures for a time Christmas morning.

We just need the trough out West to shift east under the block after New Years. But you can see how the models are showing more ridge in the East now than 3 days ago to close out the year. The wave break and record block south of Greenland is too south based next week with no room for cold 50/50 low pattern. New run Old run

The block starts out too far south next week on the latest EPS. So the EPS doesn’t leave room for a cold 50/50 low pattern. It looks like milder temperatures this run in the 6-10 day period.

The warming state of the planet has been the ultimate competing influence.

We started to see these ENSO disconnects when the 15-16 super El Niño California rainfall got delayed into the 16-17 La Niña. Then it was off to the races when the El Niño didn’t couple in 18-19. Last winter we saw weak El Niño conditions produce an 11-12 style La Niña pattern. So it’s no surprise we are getting an El Niño-like pattern with a moderate La Niña.

We have seen these strong trade wind surges and Niño 3.4 dipping temperatures back to the fall. All the competing influences have resulted in a more Niño-like pattern. Notice how the PNA is forecast to stay positive right into January. Beyond early January, it will be interesting to see which type ENSO pattern prevails.

Another El Niño-like feature that we are experiencing this month is the mild average temperature combined with the 10”+ snow in NYC . Since 1995 , all the 35.9° or warmer Decembers with 10”+ were warmer ENSO years. The snowy La Niña Decembers all had a monthly average around 32° degrees. This month is already 39.1° before the big coming solstice warm up. An interesting question to ask is how long can we keep this Niño-like pattern going? I looks like January will at least start out more Niño-like. So it will be interesting to see which ENSO type pattern shows up in February. Warmest Decembers highlighted...NYC snowfall....average temperature....Niño 3.4 temperature.... Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Dec Click column heading to sort ascending, click again to sort descending. Rank Year Total Snowfall Temp/ Niño 3.4 1 2010 20.1 32.8/-1.6 2 2003 19.8 37.6/+0.4 3 2000 13.4 31.1/-0.7 4 2009 12.4 35.9/+1.6 5 1995 11.5 32.4/-1.0 6 2002 11.0 36.0/+1.1 7 2020 10.5 39.1/-1.2

NYC is on track for its first Christmas with a morning high of 55-60 and an evening low in the 20s. Our new era of big temperature swings continues. The previous coldest temperature on Christmas with such a warm high was 33° in 2008. 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 Snowfall Snow Depth 2015-12-25 66 57 0.01 0.0 0 1982-12-25 64 41 0.02 0.0 0 1889-12-25 64 43 0.00 0.0 M 2014-12-25 62 44 0.09 0.0 0 1940-12-25 62 38 0.00 0.0 0 1979-12-25 61 50 0.87 0.0 0 1964-12-25 60 49 T 0.0 0 1994-12-25 59 41 T 0.0 0 1965-12-25 59 47 0.65 0.0 0 1932-12-25 59 47 0.13 0.0 0 1893-12-25 58 45 0.00 0.0 M 2008-12-25 57 33 0.13 0.0 0 1936-12-25 56 40 0.00 0.0 0 1933-12-25 55 34 0.00 0.0 0 1915-12-25 55 38 0.01 0.0 0

Yeah, this month looks like a continuation of the atmospheric coupling weirdness of recent years. The 500 mb pattern is much more El Niño-like. Especially the deep Aleutian Low and +PNA. I guess that this makes up for the last 2 winters which were technically El Niño with La Niña-like 500 mb patterns.

The Euro has one of the strongest south based blocks that we have seen this time of year. It has a whopping +6 SD 500 mb height anomaly just south of Greenland. A 584 dm ridge east of Newfoundland should be very close to the record in late December.

The timing of the Christmas cold front looks to be early Christmas morning. The EURO and new GFS V16 are pretty close. So the high for the day will be early with falling temperatures after. Another big temperature swing weather pattern.