bluewave

The primary low is a Great Lakes cutter so the coast will be too warm. If the primary got squashed to Pittsburgh, then the secondary would take a colder track SE of LI with good coastal snows. The secondary tracking right over NYC is only great for the interior crew.

Remember, getting pushed back doesn’t mean we won’t eventually get a 4-6” snow in NYC. While we don’t have the 2010 record blocking, models were showing snowstorms long range for all of December 2010. So the snowy pattern got delayed by 3 weeks or more depending on the model. But sometimes pushback patterns ultimately disappoint. So we would be happy with something in between a shutout and historic KU. Most would be happy with a 4-6”+ event in NYC from late December into early January. Plus several 1-3” 2-4” type snows to put us into double digits by January 10th.

I think the reason models do so much better with primary lows cutting to our west day 6-10 is that they can be off by 500 miles or more and still verify. A primary low can track 50 miles west of NYC and bring mostly rain to the coast. Same goes for a primary cutting near Chicago. But a benchmark storm can’t very from 6-10 day out if the margin of error results in 500 mile track errors. So the normal day 6-10 day model track error isn’t precise enough to handle benchmark tracks. But they have much more leeway in the margin of error for a track to our west.

The models did a good job seeing the primary low cutting from 8-10 days out for around the 15th. It was the 11-15 day runs which had a KU pattern. So that’s what is meant by getting pushed back. Now the threat before Christmas is beginning to get pushed back. Go back to the beginning of this thread in late November when the ensembles had a great looking 11-15 day pattern after December 5-7. That is not to say that we won’t get lucky late December into early January. We just need to see it day 8-10 first in order to lock it in.

I think when the crew on here hears pattern change, the main understanding is that it means 4-6”+ snowstorms will verify. They don’t think of it much in terms of what the teleconnections like the PNA and AO are doing. It can also mean a period of colder temperatures following a warmer one. But many will not call this a full pattern change unless decent snowstorms come with it.

Yeah, 0.6 is the effective skill forecast number on the verification charts.The EPS, GEPS, and GEFS all dip below that number around 10 days out. So that is the range of usefulness. https://www.emc.ncep.noaa.gov/users/verification/global/gefs/ops/geo/

The whole crew here has pretty much figured out through trial and error the the effective model range is about 8-10 days.

Yeah, the ensembles have been trying to improve the Pacific day 11-15 for weeks now. They show a great +PNA and trough near the Northeast. But as we get closer to day 8-10, the OP runs start showing cutters. Someone commented on how the OP GFS has been showing cutters day 11-15 while the GEFS has been cold. We can remember the KU look the ensembles had for Friday only to become a Great Lakes cutter with a secondary passing right over NYC. 360 hr EPS forecast for December 15th 60 hr EPS forecast for December 15th

Yeah, the trough in the West is undercutting the block to the north. So the primary lows track to the Great Lakes. Need a strong Rockies ridge to make the pattern favorable for 4”+ snows in NYC. The lag between the December -4.0 and -4.9 AO and the 4”+ snowstorms has been quite variable. The only thing that we know for sure is that the 4.0”+ snowstorm will take longer than 2000 and 1995. -4.0 to -4.9 December -AO dates and the next 4.0” snow in NYC 12-23-00…12-30…12” 12-18-95….12-19….7.7” 12-26-68….2-9….15.3” 12-13-66…12-24….7.1” 12-31-62….1-26…..4.2” 12-23-50…..None

Nothing in modern times compares to 76-77 for the duration of the extreme cold and ice build up on the local waterways from late December into early February. 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 27 to Feb 7 Missing Count 1 1918-02-07 19.4 0 2 1881-02-07 21.8 0 3 1977-02-07 22.3 0 4 1893-02-07 24.3 0 5 1888-02-07 24.5 0 6 1912-02-07 24.7 0 7 1875-02-07 24.9 4 8 1920-02-07 25.0 0 - 1886-02-07 25.0 0 9 1948-02-07 25.3 0 10 1904-02-07 25.4 0 11 1994-02-07 25.8 0

Yeah, that was the lowest monthly average. But I believe January 1985 stands as the lowest daily. That was the last time Newark almost made it to -10. https://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.ao.index.b500101.current.ascii 1985 1 19 -6.226 Data for January 1, 1985 through January 31, 1985 Click column heading to sort ascending, click again to sort descending. Name Station Type Lowest Min Temperature SEABROOK FARMS COOP -24 HIGH POINT PARK COOP -16 ESSEX FELLS SERVICE BLDG COOP -14 BOONTON 1 SE COOP -14 Trenton Area ThreadEx -12 CHARLOTTEBURG RESERVOIR COOP -12 RINGWOOD COOP -12 EWING 3 WNW COOP -12 NEWTON COOP -11 Belvidere Area ThreadEx -10 CRANFORD COOP -10 LONG VALLEY COOP -10 BELVIDERE BRIDGE COOP -10 MOORESTOWN 4 E COOP -10 Atlantic City Area ThreadEx -9 MORRIS PLAINS 1 W COOP -9 SUSSEX 1 NW COOP -9 ATLANTIC CITY INTL AP WBAN -9 Newark Area ThreadEx -8 NEWARK LIBERTY INTL AP WBAN -8

Your best snowfall combination since 1981 is a -AO and El Niño. But occasionally a La Niña with a -AO will work. The last good La Niña -AO combo for you guys was 1999-2000. It came down to the late January event when we got the -AO dip. Snowfall since 1981 Time Series Summary for Baltimore Area, MD (ThreadEx) - Oct through Sep Click column heading to sort ascending, click again to sort descending. Rank Season Total Snowfall ENSO and AO 1 2009-2010 77.0 El Niño -AO 2 1995-1996 62.5 La Niña -AO 3 2002-2003 58.1 El Niño - AO 4 2013-2014 39.0 Neutral 5 1982-1983 35.6 El Niño -AO 6 1986-1987 35.2 El Niño -AO 7 2015-2016 35.1 El Niño -AO 8 2014-2015 28.7 El Niño +AO 9 1999-2000 26.1 La Niña -AO 10 1981-1982 25.5 Neutral -AO

I think that it’s mostly the warmer waters to our east and overall higher temperatures favor interior sections in December. Notice the wide spread between BGM and ISP snowfall in December. But they both have had the same January snowfall as the coast gets cold enough for more snow. Monthly Total Snowfall for BINGHAMTON (GREATER AP), NY Click column heading to sort ascending, click again to sort descending. Year Dec Season Mean 16.0 16.0 2015 2.2 2.2 2016 29.8 29.8 2017 11.3 11.3 2018 7.9 7.9 2019 20.1 20.1 2020 48.2 48.2 2021 8.5 8.5 2022 0.3 0.3 Monthly Total Snowfall for ISLIP-LI MACARTHUR AP, NY Click column heading to sort ascending, click again to sort descending. Year Dec Season Mean 2.7 2.7 2015 T T 2016 3.2 3.2 2017 6.0 6.0 2018 T T 2019 4.2 4.2 2020 7.5 7.5 2021 0.3 0.3 2022 0.0 0.0 Monthly Total Snowfall for Binghamton Area, NY (ThreadEx) Click column heading to sort ascending, click again to sort descending. Year Jan Season Mean 16.2 16.2 2015 16.1 16.1 2016 10.2 10.2 2017 12.0 12.0 2018 14.9 14.9 2019 26.2 26.2 2020 12.7 12.7 2021 16.8 16.8 2022 20.3 20.3 Monthly Total Snowfall for ISLIP-LI MACARTHUR AP, NY Click column heading to sort ascending, click again to sort descending. Year Jan Season Mean 15.9 15.9 2015 30.2 30.2 2016 24.8 24.8 2017 14.0 14.0 2018 22.0 22.0 2019 0.9 0.9 2020 2.5 2.5 2021 1.1 1.1 2022 31.8 31.8

Yeah, all-time record warmth for Northern Alaska in December with such strong blocking. So the polar vortex gets displaced to the south over North America. The lingering influence from the record -EPO block in November has changed our typical warm up pattern around the solstice.

Those steep mid-level lapse rates would support a wet snow in Suffolk with light accumulations on the colder surfaces.

An east-west block from Alaska to Greenland with energy cutting underneath is usually a KU signal even for the coast. But the elongated trough from coast to coast is an oddity. We should have more of a ridge over the Rockies with so much blocking. This is what happened back in December 2000. But the models let the primary run too far north due to the lower heights in the Western US. Classic KU composite from December 2000 Odd trough under the whole length of block with no ridge in Rockies

This has to be one of the oddest combinations of teleconnections that we have seen in a while. We usually get a solid Rockies Ridge +PNA spike with so much blocking from Greenland back to Alaska. But we have an unusual east to west trough stuck underneath. There is still a tail of blue behind the cutoff back to the Rockies next weekend. So there is nothing keeping the primary low from cutting to Chicago even several days after a -4 AO block.The secondary low hugs the coast for plenty of rain and wind before ending as some snow. Never seen a 500 mb look like this before

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.