bluewave

We can add one of the highest recorded 250mb jet stream winds above Green Bay to the list of extremes this month.

Some of the warmest December minimum temperatures on record around the region this month. POU recorded the 3rd warmest minimum. Only the 5th time that HPN didn’t drop below 20°. It was also the 5th time that NYC didn’t drop below 25°. Many of the top 5 warmest were in recent years. Time Series Summary for Poughkeepsie Area, NY (ThreadEx) - Month of Dec Click column heading to sort ascending, click again to sort descending. Rank Year Lowest Min Temperature Missing Count 1 2015 24 0 2 1996 18 0 3 2021 16 4 - 2014 16 0 - 2006 16 0 4 2011 14 0 - 1974 14 0 - 1957 14 0 5 2018 13 0 - 1984 13 0 - 1972 13 0 Time Series Summary for WESTCHESTER CO AP, NY - Month of Dec Click column heading to sort ascending, click again to sort descending. Rank Year Lowest Min Temperature Missing Count 1 2015 28 0 2 2012 24 0 3 2021 20 5 - 2014 20 1 - 1984 20 0 4 2018 19 1 - 1997 19 8 - 1996 19 8 - 1974 19 0 5 2011 18 0 - 2001 18 0 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 Lowest Min Temperature Missing Count 1 2015 34 0 2 2012 28 0 3 1974 26 0 4 2021 25 4 - 1984 25 0 5 2018 24 0 - 2014 24 0 - 1908 24 0

At least the Sierras are getting some much needed snowpack.

Almost like a cold season version of what happened with the extreme heat in the PACNW last summer.

Not that much cold this year as Newark is near the warmest year on record with 5 days to go. Islip is in 4th place. You can see how many top 10 warmest years there were just since 2010. Time Series Summary for NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending. Rank Year Mean Avg Temperature Missing Count 1 2021 58.0 5 2 2012 57.8 0 3 1990 57.5 0 4 2020 57.3 0 - 2011 57.3 0 5 2016 57.2 0 - 1998 57.2 0 6 2010 57.0 0 - 2006 57.0 0 - 1973 57.0 0 7 1991 56.9 0 8 2002 56.5 0 - 1993 56.5 0 9 2017 56.4 0 10 1999 56.3 0 Time Series Summary for ISLIP-LI MACARTHUR AP, NY Click column heading to sort ascending, click again to sort descending. Rank Year Mean Avg Temperature Missing Count 1 2012 55.2 0 2 1998 55.0 0 3 2020 54.9 0 4 2021 54.7 5 - 2016 54.7 0 5 1999 54.3 0 6 2017 54.2 0 - 2011 54.2 0 - 1991 54.2 0 - 1990 54.2 0 7 2010 54.0 0 8 2006 53.9 0 9 2018 53.7 0 10 2002 53.6 0

More ridiculous December heat for the next 5 days will give DFW the warmest December on record by a wide margin. Time Series Summary for Dallas-Fort Worth Area, TX (ThreadEx) - Month of Dec Click column heading to sort ascending, click again to sort descending. Rank Year Mean Avg Temperature Missing Count 1 2021 60.2 6 2 1933 54.0 0 3 2015 53.6 0 4 1970 53.5 0 5 1965 52.8 0 - 1939 52.8 0

Really extreme sounding warmth under the record Aleutians Ridge.

Still some trees with leaves for the first snowfall in NYC.

Yeah, it’s a big challenge trying to figure out the week 3-4 forecast based on week 1-2. Analog roll forwards beyond week 2 can be very low skill. Older analogs from colder eras haven’t been working very well in our post 2010 warmer climate. There is also a small sample size issue since many patterns have unique features that don’t repeat in the same ways. Plus we have random events like wave breaks which analogs won’t work for. Maybe machine learning will be the next big leap forward in long range forecasting. I think that’s what the ECWMF is researching for improvement to the weeklies and seasonal forecasts.

It seems like the EPS weeklies only have skill beyond 15 days when a pattern change happens during week 1. This works well when the new pattern lasts at least 4 weeks. But many pattern changes first show up on the EPS radar between days 8-15. So in those cases, the old week 3 forecast can be way off. I am not sure how many times the weeklies have correctly predicted a pattern change that happened beyond week 2.

More records with the extreme December Aleutians Ridge.

This was the 5th Christmas at Newark to reach 55° since 2008. Data for December 25 - NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending. Date Max Temperature Min Temperature Precipitation Snowfall Snow Depth 1964-12-25 69 44 0.01 0.0 0 1982-12-25 68 40 0.02 0.0 0 2014-12-25 64 41 0.10 0.0 0 2015-12-25 63 54 0.03 0.0 0 2020-12-25 62 28 0.66 0.0 0 1940-12-25 61 32 0.00 0.0 0 1994-12-25 60 41 T 0.0 0 1979-12-25 59 47 0.37 0.0 0 1965-12-25 59 40 0.85 0.0 0 1936-12-25 57 36 0.00 0.0 0 2021-12-25 55 38 0.16 0.0 0 2008-12-25 55 33 0.11 0.0 0

NYC Metro has been the only region in the I-95 corridor that hasn’t been able to surpass the 95-96 snowfall totals since 2010. We could have done it in 10-11 if the snows didn’t shut off at the end of January. The best snows missed to our NE in 14-15 and to our S in 09-10. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Rank Ending Date Total Snowfall Oct 1 to Apr 30 Missing Count 1 1996-04-30 75.6 0 2 1948-04-30 63.9 0 3 2011-04-30 61.9 0 Time Series Summary for Boston Area, MA (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Ending Date Total Snowfall Oct 1 to Apr 30 Missing Count 1 2015-04-30 110.6 0 2 1996-04-30 107.6 0 3 1994-04-30 96.3 0 Time Series Summary for Philadelphia Area, PA (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Ending Date Total Snowfall Oct 1 to Apr 30 Missing Count 1 2010-04-30 78.7 0 2 2014-04-30 68.0 0 3 1996-04-30 65.5 0 Time Series Summary for Baltimore Area, MD (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Ending Date Total Snowfall Oct 1 to Apr 30 Missing Count 1 2010-04-30 77.0 0 2 1996-04-30 62.5 1 3 2003-04-30 58.1 0 Time Series Summary for Washington Area, DC (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Ending Date Total Snowfall Oct 1 to Apr 30 Missing Count 1 2010-04-30 56.1 0 2 1899-04-30 54.4 0 3 1996-04-30 46.0 0

December is our fastest warming winter month. That’s why the new climate 1991-2020 climate normals have the greatest winter temperature increase in December. The only colder than average December in the last decade was 2017. New 1991-2020 climate normals compared to 1981-2010 EWR Dec….38.0….36.5….+1.5 Jan….32.8….31.6…..+1.2 Feb….35.1….34.6…..+0.5 Avg…..35.3….34.2….+1.1 NYC Dec….39.1…..37.5….+1.6 Jan….33.7…..32.6...+1.1 Feb….35.9….35.3….+0.6 Avg…..36.2…35.1….+1.2 LGA Dec…40.0….38.2….+1.8 Jan….34.4….32.9….+1.5 Feb….36.3….35.3….+1.0 Avg….36.9….35.5…..+1.4 JFK Dec….38.3….37.7….+0.6 Jan…..32.8….32.7….+0.1 Feb….34.5….34.9…..+0.4 Avg….35.2….35.1…..+0.1 ISP Dec….37.1…..35.6…..+1.5 Jan….31.9….30.6…..+1.3 Feb...33.3….32.8…..+0.5 Avg….34.1….33.0…..+1.1 BDR Dec…37.0….35.4….+1.6 Jan….31.4….30.1….+1.3 Feb….33.1….32.4….+0.7 Avg…..33.8…32.6….+1.2 HPN Dec…35.1….33.6….+1.5 Jan….29.8….28.3…+1.5 Feb….31.9….30.9….+1.0 Avg…..32.6….30.9…+1.4

Near 50° passes for close to normal over the last 10 years on Christmas. Data for December 25 - NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending. Date Max Temperature Min Temperature Precipitation Snowfall Snow Depth 2020-12-25 62 28 0.66 0.0 0 2019-12-25 48 27 0.00 0.0 0 2018-12-25 42 29 0.00 0.0 0 2017-12-25 38 28 0.20 0.1 0 2016-12-25 52 34 0.00 0.0 0 2015-12-25 63 54 0.03 0.0 0 2014-12-25 64 41 0.10 0.0 0 2013-12-25 30 19 0.00 0.0 0 2012-12-25 43 31 0.02 0.0 0 2011-12-25 48 25 0.00 0.0 0 Summary Maximum Temperature Maximum Average Minimum Percent of Years >=100° F >=90° F >=50° F <=32° F 64 49.0 30 0 0 40% 10%

Getting close to 50° now with breaks of sun.

The CPC commented on how unusual this type of MJO stall in the WPAC is. Dynamical model MJO index forecasts depict a fairly unusual setup, with a persistent West Pacific signal over the next couple of weeks suggesting the evolution of a lower-frequency mode than MJO.

New Aleutians ridge and -PNA record for this time of year.

Yeah, I can remember the discussion of this paper a while back. So it’s possible the QBO could be a piece of the puzzle. The +500 mb height anomaly south of the Aleutians driving the -PNA is on track to be the strongest on record for December. https://agupubs.onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1002%2F2017GL076929&file=grl57089-sup-0001-2017GL076929-SI.docx https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076929 Storm tracks, defined as the preferred regions of extratropical synoptic-scale disturbances, have remarkable impacts on global weather and climate systems. Causes of interannual storm track variation have been investigated mostly from a troposphere perspective. As shown in this study, Northern Hemisphere winter storm tracks are significantly modulated by the tropical stratosphere through the quasi-biennial oscillation (QBO). The North Pacific storm track shifts poleward during the easterly QBO winters associated with a dipole change in the eddy refraction and baroclinicity.

Another all-time highest temperature for December.

I was agreeing with the post that I was replying to. It can snow in warm winter patterns. We saw this with the 16-17 winter which had more DJF snow than 18-19 which was colder. The more favorable Pacific intervals in 16-17 made the difference.

The extreme of snow in November 2018 was a result of the very favorable Pacific and record -EPO. Your point about comparing two different months doesn’t change the fact the the average monthly temperatures were the same. So you are actually agreeing with me that’s it’s more about storm track and teleconnections than the temperatures.

Central Park 0.2 in 0700 AM 12/24 Official NWS Obs

Our snow amounts seem to be more a function of storm track and teleconnections than temperature. We just got a light snow event today with an average NYC December temperature of 44.1°. We had a much more favorable Pacific in November 2018 and NYC picked up 6.4” of snow with an average temperature of 44.4°. So favorable patterns can produce more snow than the same temperature in a less favorable pattern. The January average temperature in 2019 was 32.5° and NYC got 1.1” of snow. But a much warmer January 2012 picked up 4.3” with a 37.3° average temperature. The difference between the two years was that the pattern in 2012 allowed a better storm track for one day than the whole month of January 2019 got. But it’s easier for NYC to reach 50” of snow if they get extended cold like 14-15. We had close to a 40-40 winter for parts of area in 2016 and 2017. But the 40° winter in 11-12 only produced single digit seasonal snowfalls for many. Factors like storm track and Pacific favorability play a large role in snowfall amounts for us.

This was the fourth warmest first three weeks of December in NYC. 8 out of the 10 warmest average temperatures occurred since the late 90s. The most recent La Ninas this warm in December were 2011, 1998, and 1999. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Rank Ending Date Mean Avg Temperature Dec 1 to Dec 21 Missing Count 1 2015-12-21 50.2 0 2 2001-12-21 48.9 0 3 1998-12-21 48.7 0 4 2021-12-21 44.8 0 5 2012-12-21 44.7 0 6 2011-12-21 43.9 0 7 1999-12-21 43.7 0 - 1984-12-21 43.7 0 8 2006-12-21 43.5 0 - 1923-12-21 43.5 0 9 1990-12-21 43.3 0 10 1956-12-21 43.2 0