bluewave

This is one of those rare times during a La Niña that the Pacific blocking does better than the 11-15 day forecast. New run for late week storm Old day 11-15 day range runs

One of the few Decembers when the AO made it to -4 or lower. https://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.ao.index.b500101.current.ascii https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/norm.daily.ao.nao.pna.aao.gdas.120days.csv 10Dec2022 -4.0676 Decembers with a -4 or lower reading 2022 2000 1995 1968 1966 1962 1950 Lower than -5 2010 2009 1976

https://www.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=pmdepd The GFS was not included in tonights blend past day 4 at all. The ensemble means again support low development most consistent with the ECMWF.

Maybe that record -EPO block back in November changed our typical pattern of recent years? https://www.cpc.ncep.noaa.gov/products/intraseasonal/z500_nh_anim.shtml https://downloads.psl.noaa.gov/Public/map/teleconnections/epo.reanalysis.t10trunc.1948-present.txt

NYC snowfall 2000 12 29 -4.688…13.4” 1995 12 19 -4.353…11.5” 1962 12 31 -4.159…4.5”

We’ll probably need the primary to squeeze south of Chicago in order for the the secondary to take a benchmark instead of hugger track. You can see 12z Euro comparison with the 6z GFS. That Euro primary cut just a little too far north. If the 12z guidance has any clue, then the 12z GFS extreme suppression track looks like an outlier. So maybe this will turn out to be a battle between a benchmark or hugger track. Something in between those two would work.

AO getting closer to -4 which would increase the chances of more blocking JFM and a possible SSW. https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/norm.daily.ao.nao.pna.aao.gdas.120days.csv 09Dec2022-3.6473

Yeah, the only reason the 6z GFS has a nice snowstorm is due to the skinny Rockies Ridge and +PNA spike closer to neutral. This scenario is showing up in the ensembles. So to me, all these OP runs beyond 120 are just ensemble members anyway.

The EPS mean has several members near the BM with a little Rockies Ridge + PNA spike.

Great -EPO -AO pattern. But the -PNA pumps the SE ridge next week on the Euro and GEM allowing the storm to tuck in. So you can see the Euro and GEM keeping this an interior snow event for now. Need the +PNA Rockies Ridge idea of the Euro control for snow at the coast and a 982mb BM track. Snowier Euro control 982 mb BM track

It’s tough to compare analogs until the full monthly 500 mb composite is in. But the common theme of both months is a -PNA -AO. So we’ll need to verify some Pacific improvement in order to have a shot at above normal December snowfall in NYC. It could be something as simple as a transient Rockies Ridge able to produce an accumulating snow. But the long range ensembles aren’t really good enough to see short term details like that.

The size of the snow events can be quite variable in the -3 to -4 -AO range during December in NYC. Anywhere from a trace to 1 to around 10.5”. So the AO dipping to around -4 in itself can’t tell you much how much snowfall NYC will get in December. We can usually count on bigger events the closer that we get to -5. That seems to be the level when the AO can start to push back against any negative Pacific influences. But a -4 in December is usually a good indication that there will be further blocking intervals JFM.

ISP has been the best spot since the super El Niño. Individual events and the highest snowfall totals 2022 Jan 28-29….Islip….24.7 2021 Jan 31-Feb 2....Blomingdale, NJ.....26.1 2020 Dec 16-17 East Tremont, NY....12.4 2019 Mar 3-4...Monroe, CT....12.0 2018 Nov 15....Mount Hope, NY.......18.3 Mar 21-22...Patchogue, NY......20.1 Mar 13...Southampton,NY.....18.3 Mar 8....New Farfield, CT..........26.8 Mar 2...Monroe, NY.................14.0 Jan 4...Islip, NY.......................15.8 2017 Mar 14...Montgomery, NY.......23.5 Feb 9...Selden, NY...................16.0 Jan 7...Orient, NY....................12.5 2016 Feb 5...Setauket, NY................12.0 Jan 23..JFK,NY.........................30.5 2015 Feb 2..New Faifield, CT............12.0 Jan 26-27....Orient,NY.............28.5 2014 Feb 13-14...Roselle, NJ............16.7 Jan 21-22....Centerreach,NY....14.0 Jan 2-3......Lindenhurst, NY.....12.5 2013 Mar 8....Harriman,NY..............15.0 Feb 8....Upton, NY..................30.9 2012 Nov 7-8.....Monroe, CT..........13.5 Jan 21......North Haven, CT....12.0 2011 Oct 29.....Harriman, NY.........16.0 Jan 26-27...NYC................... 19.0 Jan 11-12.......Meriden, CT....29.0 2010 Feb 25-26...Mount Hope, NY...27.5 Dec 26........Elizabeth, NJ........31.8 Feb. 10.....Sound Beach, NY....16.2 2009 Dec 19-20....Upton, NY..........26.3

Yeah, ISP has become the new Boston for 16”+ snowstorms since the super El Niño. There have been 4 events at ISP and only 1 at Boston. So ISP has been the place to be for big snowstorms in recent years. Maximum 2-Day Total Snowfall for ISLIP-LI MACARTHUR AP, NY Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 24.7 2022-01-29 0 2 23.7 2016-01-24 0 0 0 3 18.4 2018-03-22 0 0 4 16.0 2018-01-04 0 Maximum 2-Day Total Snowfall for Boston Area, MA (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 23.8 2022-01-29 0

Would make sense given how ISP has become the new snowfall capitol around the area.

Yeah, the 12z CMC really backed off 0z at the coast but the interior still does well. So it looks more like the Euro and GFS now. Really need a stronger closed low to get more than a T-2 or T-3 near the coast. Marginal cod air masses at the start require a very strong 500 mb closed low for rains to change to 4”+ snows at the coast this time of year.

Yeah, the NW Atlantic has warmed too much to allow SSTs as cold as the 1970s and 1980s.

While March 1993 was a unique case, it matches the general theme since the 1990s. The December to March storm tracks have shifted east over toward the warm pool. The main winter storm tracks since 2010 have been benchmark like Jan 16 or coastal hugger like Dec 2020. The NJ inland runner track hasn’t been as common. In fact, State College hasn’t had a 16”+ snowstorm since since Feb 2003.

Winter 50° days in NYC have become more common than highs that don’t get above freezing.

Yeah, their snowfall has been cut nearly in half since the early 1990s. The big lows that used to track right over NJ and dump heavy snow in Central PA have pretty much become non-existent these days. It could be related to the record warm pool favoring BM tracks instead of more like March 1993.

Things get more interesting if we take a longer look at winter temperatures and seasonal snowfall at Islip since the early 1960s. There is decrease in snow cover days and an increase in total seasonal snowfall. Sharper warming trend with nearly double the number of winter 50° days. So quick warm ups after snowstorms have resulted in quick snowmelts after the storms.

That’s a good question. While Islip snowfall has doubled since 1981, the number of days with 1” of snowfall on the ground has only increased by a few days. So it’s one of the features of our warming climate. All these 50° and 60° days around our snowstorms hasn’t allowed a big jump in snow cover days for going from near 20” to 40” since 1981. So we get quick snowmelts.

December 11-20 has been the snowiest part of the month in NYC since 2011. So it’s possible NYC could pick up its first snow of the season with this storm. Need a much stronger 500 mb low like the CMC to pick up more than a T-2”. 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 1 to Dec 10 Missing Count 2021-12-10 T 0 2020-12-10 T 0 2019-12-10 1.6 0 2018-12-10 0.0 0 2017-12-10 4.6 0 2016-12-10 0.0 0 2015-12-10 0.0 0 2014-12-10 1.0 0 2013-12-10 2.1 0 2012-12-10 0.0 0 2011-12-10 0.0 0 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 11 to Dec 20 Missing Count 2021-12-20 0.0 0 2020-12-20 10.5 0 2019-12-20 0.9 0 2018-12-20 T 0 2017-12-20 2.4 0 2016-12-20 3.2 0 2015-12-20 0.0 0 2014-12-20 T 0 2013-12-20 6.5 0 2012-12-20 0.0 0 2011-12-20 0.0 0 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 21 to Dec 31 Missing Count 2021-12-31 0.2 0 2020-12-31 0.0 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

The last time we had a top 10 coldest winter was 1976-1977. The last top 20 was 93-94. 14-15 would be the coldest of the last decade coming in at 22nd place. But while February had impressive sustained cold, the lowest temperatures never really came close to the 76-94 era around the region. It’s funny that NYC couldn’t go below 0°in February 2015, but did it in the record warm winter on Valentines Day 2016. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Rank Season Mean Avg Temperature Missing Count 1 1917-1918 25.7 0 2 1880-1881 26.5 0 3 1903-1904 27.3 0 4 1919-1920 27.4 0 5 1874-1875 27.7 4 - 1872-1873 27.7 0 6 1904-1905 28.1 0 7 1935-1936 28.3 0 8 1976-1977 28.4 0 - 1884-1885 28.4 0 - 1882-1883 28.4 0 9 1892-1893 28.6 0 - 1887-1888 28.6 0 10 1878-1879 29.0 2 11 1933-1934 29.1 0 12 1871-1872 29.5 2 13 1962-1963 29.9 0 - 1922-1923 29.9 0 - 1885-1886 29.9 0 - 1876-1877 29.9 0 14 1947-1948 30.0 0 - 1886-1887 30.0 0 - 1883-1884 30.0 0 15 1894-1895 30.2 0 16 1977-1978 30.3 0 17 1969-1970 30.5 0 - 1944-1945 30.5 0 18 1911-1912 30.7 0 19 1958-1959 30.8 0 20 1993-1994 31.1 0 - 1934-1935 31.1 0 21 2002-2003 31.2 0 - 1967-1968 31.2 0 - 1909-1910 31.2 0 - 1870-1871 31.2 4 22 2014-2015 31.4 0 - 1921-1922 31.4 0

It would be nice if some long range forecasting blogs update their climo and stop discussing winter analog packages from the colder 76-77 to 93-94 era. It’s been difficult to find many winter analogs even before the 15-16 super El Niño that are still valid. But discussing analogs from colder eras seems to bring a sense of nostalgia so I can understand where it is coming from. But the likelihood of seeing a repeat of January 1977, 1982, 1985, or 1994 is pretty much nonexistent in our much warmer world.