bluewave

From all the historical accounts that I have read, the winter of 1779-1780 was probably the coldest on record going back to the colonial times. If this Philly account of the temperature only getting above freezing once in January 1780 is close, then the monthly average may have only been around 15°. The coldest month on record since 1874 was January 1977 at 20.0°. https://www.google.com/books/edition/The_Philadelphia_Area_Weather_Book/mon_ivVXUY4C?hl=en&gbpv=1&dq=january+1780+cold+philadelphia+pa&pg=PA76&printsec=frontcover Time Series Summary for Philadelphia Area, PA (ThreadEx) - Month of Jan Click column heading to sort ascending, click again to sort descending. Rank Year Mean Avg Temperature Missing Count 1 1977 20.0 0 2 1893 24.0 0 3 1918 24.1 0 4 1970 24.5 0 5 1982 24.7 0

These extreme rainfall events have become the new normal for us since 2003. Many years in NYC have finished above 50.00”. Plus if this comes far enough west for high winds, this has been a repeating theme since 2010. Time Series Summary for NY CITY CENTRAL PARK, NY - Jan through Dec Click column heading to sort ascending, click again to sort descending. Rank Year Total Precipitation Missing Count 1 1983 80.56 Rain gauge malfunction so total likely overdone 2 2011 72.81 0 3 1972 67.03 0 4 2018 65.55 0 5 1989 65.11 0 6 2007 61.67 0 7 1975 61.21 0 8 1990 60.92 0 9 2006 59.89 0 10 2021 59.73 0 11 2003 58.42 0 12 1903 58.32 0 13 1889 58.18 0 14 1913 58.00 0 15 1973 57.23 0 16 1984 57.03 0 17 1971 56.77 0 18 1996 56.19 0 19 1927 56.06 0 20 2005 55.97 0 21 2023 55.21 19 22 1977 54.73 0 23 2014 53.79 0 24 2009 53.62 0 25 2008 53.61 0 26 1933 53.53 0 27 1888 53.32 0 28 1919 53.29 0 29 1920 53.20 0 30 2019 53.03 0 31 1937 52.97 0 32 1902 52.77 0 33 1884 52.25 0 34 1979 52.13 0 35 2004 51.93 0 36 1871 51.38 0

12z Euro correcting warmer for our annual warm up around the solstice. New run Old run

It’s the same pattern in the ensemble means.

The main reason to be skeptical the OP CMC single digits just west of NYC at 10 days is that it’s a big cold outlier among it’s ensembles along with the GEFS and GEPS. This is why it’s much better to use ensemble means beyond 5 days. The ensembles are pretty good at this range but their have been numerous runs way too cold from the OP at days 7-10.

This has to be one of the most extreme VP anomaly signatures in the general MJO 6-7 regions for this time of year. The Pacific Jet extension and record breaking ridge and warmth over the Northern Tier and Canada are a perfect match for forcing in that location. Unfortunately, the warmth following these jet extensions can last a few weeks which the models are showing.

Only the 4th time on record that suburbs like Westchester couldn’t drop below 28° during the first 12 days of December. Time Series Summary for WESTCHESTER CO AP, NY Click column heading to sort ascending, click again to sort descending. Rank Ending Date Lowest Min Temperature Dec 1 to Dec 12 Missing Count 1 1998-12-12 36 6 2 2015-12-12 29 0 - 1953-12-12 29 1 3 2023-12-12 28 0

But only enough to qualify for decadal snow cover extent lows this time of year in North America. https://www.star.nesdis.noaa.gov/smcd/emb/snow/HTML/snow_extent_monitor.html

This may be the warmest day 10-15 EPS signal I ever saw for Canada this time of year.

The general storm signal is pretty high following the record 500 mb ridge forecast for the Upper Midwest in a few days. But the track is still uncertain.

Those are going to be some extreme December monthly departures for places like International Falls as they are already at +11.9. Time Series Summary for International Falls Area, MN (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Ending Date Mean Avg Temperature Dec 1 to Dec 11 Missing Count 1 2015-12-11 32.4 0 2 1913-12-11 30.3 0 3 1920-12-11 28.6 0 4 1999-12-11 27.9 0 5 2023-12-11 27.6 0 6 1923-12-11 27.0 0 7 2020-12-11 26.6 0 8 1952-12-11 25.0 0 9 1967-12-11 24.8 0 10 1998-12-11 24.6 0

Yeah, most of the people that I discuss the warmer winters with off this forum are really happy about the milder winters. We seem to be in the minority in liking colder and snowier winters. There are many people who can’t wait to head south when they retire.

The one bright spot with near record warm CONUS December patterns is lower heating bills.

It seems like the start of the more hostile Pacific pattern began in December 11. But it didn’t become more widespread through the winters until 18-19. So in the last 13 Decembers including this one, we only had 3 with a favorable enough Pacific for 6”+ snows in NYC. The years were 2013, 2017, and 2020. Allsnow gets credit for calling the December 2020 pattern potential pretty early.

That December 2000 to 2010 record was the first 11 year run with 5 double digit snowfall years since the 1880s. The 1940s were great also with 3 double digit years. Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Dec Season Mean 8.9 8.9 2010 20.1 20.1 2009 12.4 12.4 2008 6.0 6.0 2007 2.9 2.9 2006 0.0 0.0 2005 9.7 9.7 2004 3.0 3.0 2003 19.8 19.8 2002 11.0 11.0 2001 T T 2000 13.4 13.4 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Dec Season Mean 7.5 7.5 1880 11.5 11.5 1881 1.3 1.3 1882 0.0 0.0 1883 22.6 22.6 1884 10.7 10.7 1885 T T 1886 10.3 10.3 1887 9.0 9.0 1888 T T 1889 6.0 6.0 1890 11.4 11.4 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Dec Season Mean 8.7 8.7 1940 3.0 3.0 1941 0.3 0.3 1942 8.5 8.5 1943 T T 1944 6.7 6.7 1945 15.6 15.6 1946 1.3 1.3 1947 30.2 30.2 1948 25.3 25.3 1949 1.3 1.3 1950 3.8 3.8

Double digit event on the 19-20th. Data for December 19, 2009 through December 20, 2009 Click column heading to sort ascending, click again to sort descending. State Name Station Type Total Snowfall NY SHOREHAM 1.8 SSE CoCoRaHS 29.0 NY ISLIP-LI MACARTHUR AP WBAN 23.9 NY EAST MORICHES 0.6 WNW CoCoRaHS 23.2 NY RIVERHEAD RESEARCH FARM COOP 20.0 NY JAMESPORT 0.6 SSW CoCoRaHS 20.0 NY BAITING HOLLOW COOP 19.0 NY ISLIP 0.2 NW CoCoRaHS 17.0 NY JFK INTERNATIONAL AIRPORT WBAN 14.5 NY OCEANSIDE COOP 14.2 CT NORWICH PUBLIC UTILITY PLANT COOP 14.0 NY NORTHPORT 1.6 NNE CoCoRaHS 13.8 NY LEVITTOWN 0.2 E CoCoRaHS 13.5 NY FLORAL PARK 0.4 W CoCoRaHS 13.5 NJ NEWARK LIBERTY INTL AP WBAN 11.2 NY CENTERPORT COOP 11.0 NY NY CITY CENTRAL PARK WBAN 10.9 NY MINEOLA COOP 10.2

It’s as if the Boxing Day Blizzard flipped the switch to very little snowfall from December 20th-31st. This has become one of our least snowy 10-11 day periods of winter. The most disruptive Christmas event of the last decade was the flood cutter in 2020 which wiped out the BGM 40” snowpack leading to all the flash flooding. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Ending Date Total Snowfall Dec 20 to Dec 31 Missing Count 2022-12-31 T 0 2021-12-31 0.2 0 2020-12-31 T 0 2019-12-31 T 0 2018-12-31 T 0 2017-12-31 0.7 0 2016-12-31 T 0 2015-12-31 T 0 2014-12-31 T 0 2013-12-31 T 0 2012-12-31 0.4 0 2011-12-31 0.0 0 2010-12-31 20.0 0

Yeah, the warmth from MJO and El Niño induced Pacific Jet extension is going to be around for a while. When you see such a deep trough south of Alaska and strong ridge over Canada it keeps the Pacific Jet aimed at the West Coast. Plus we are going to lose the -AO and -NAO blocking. But this has been par for the course in December in recent years. So expectations have been lowered especially early on during El Niños. https://globalcryospherewatch.org/state_of_cryo/snow/

Whenever Canada gets this warm, the North American snow cover extent goes way down. https://globalcryospherewatch.org/state_of_cryo/snow/

While it’s tough to say exactly how far above +10° the departures finish in Canada, some of the warmth records so far have been pretty impressive.

Same for me. I originally had +2.5 to +5.0 range for the various NYC metro stations. I use a 2.5° scale. -2.5 to -5.0…0 to -2.5…0 to +2.5…+2.5 to 5.0. On my map the +2.5 line is just to our south this month. And the +5.0 is to our NW closer to the Great Lakes. There may also be a 10+ departure region this month in the Upper Midwest near International Falls. Currently +4.5 for EWR….NYC….+4.6…ISP….+4.1.

December during the 1870s and 1880s in NYC were very cold. The 1890s were significantly warmer. I started the groupings on the 1s since that is the first year for each new climate normals period. So December temperatures in NYC since 2011 have been similar to Novembers in the 1870s. NYC Dec Avg Temperature 1871-1880…31.9° 1881-1890…33.8° 1891-1900…36.1° 1901-1910…34.1° 1911-1920…34.8° 1921-1930…35.2° 1931-1940°…36.2° 1941-1950°…35.0° 1951-1960°….36.4° 1961-1970°….35.1° 1971-1980°….37.1° 1981-1990….37.5° 1991-2000…38.3° 2001-2010….37.9° 2011-2020….40.6° Monthly Mean Avg Temperature for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Nov Season Mean 41.4 41.4 1880 38.9 38.9 1879 42.9 42.9 1878 44.1 44.1 1877 44.2 44.2 1876 45.1 45.1 1875 38.9 38.9 1874 42.8 42.8 1873 37.2 37.2 1872 41.4 41.4 1871 38.8 38.8 Monthly Mean Avg Temperature for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Dec Season Mean 40.6 40.6 2020 39.2 39.2 2019 38.3 38.3 2018 40.1 40.1 2017 35.0 35.0 2016 38.3 38.3 2015 50.8 50.8 2014 40.5 40.5 2013 38.5 38.5 2012 41.5 41.5 2011 43.3 43.3

It was the cold in February which allowed the Southeast to cash in. https://www.weather.gov/ilm/Feb1973Snow One of the greatest snowstorms in Southeastern United States history occurred February 9-11, 1973. This storm dropped one to two feet of snow across a region that typically sees only an inch or two of snow per year. New all-time snowfall records were established in a number of locations including Rimini, SC with 24 inches; 18 inches in Darlington, SC; and 16.5 inches in Macon, GA. Snowfall in Wilmington, NC reached 12.5 inches with 7.1 inches recorded in Charleston, SC, both setting all-time records which were broken just 16 years later during the Christmas snowstorm of 1989. Measurable snow fell along the Gulf Coast from Texas to Florida and flurries were reported as far south as Lisbon and Clermont, Florida just outside of Orlando.

Yeah, but some on here won’t consider 50s that big a deal in later December since it’s much cooler than the low 70s reached in 2015 and +33 departure.

They also put out a separate 15 year climate normals but it’s not as widely used as the 30 years. The main challenge of using climate normals in a rapidly warming climate is that it masks the warming. With the new 39.1 average December temperature in NYC, they only need a +3.4 departure to enter the top 10 warmest of December average temperatures. And we hear the sentiment on here that a +3.4 really isn’t anything out of the ordinary since it’s much lower than the +13.3° and 50° December 2015. Plus we have had something like 20-30 top 10 warmest months of the year depending on the local station used to only one top 10 coldest since 2015. 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 Mean Avg Temperature Missing Count 1 2015 50.8 0 2 2001 44.1 0 3 2021 43.8 0 4 1984 43.7 0 5 2006 43.6 0 6 2011 43.3 0 7 1998 43.1 0 8 1982 42.7 0 9 1990 42.6 0 10 1891 42.5 0