bluewave

The issue with the Pacific blocking not being able to hold is more a Northern Stream function of lowering heights out West too much with the added shortwaves in the fast flow becoming kickers. A dominant STJ that is strong enough usually has better wave spacing allowing more amplitude and less suppression. Sometimes suppression can become an issue with El Niños which are too weak like 79-80.

Block amplification issues usually occur with a dominant Northern Stream. Plus this block isn’t that strong. Remember back in 2010 with the record STJ and wall to wall -3 to -5 -AO days how the systems had no trouble eventually coming north after 2-6-10. Pure -AO suppression is rare with a strong enough STJ. It only really happened once on 2-6-10. But that was one of the strongest -AOs on record. This event is much weaker. Then the snows eventually came north so only one system was blocked.

The GEFS generates some impressive Arctic air to our West for a week 2 ensemble mean.

We want a Southeast Ridge since most of the NYC 4”+ snowfalls this time of year have occurred right before or after a 50° day. Very tough to generate snow here with steady below average cold and no warm ups. The cold that starts building out West with the -PNA could be more impressive than what we will see over the next few weeks. So maybe we get a big cutter and a 50° day followed by a cool down and overrunning hugger snowfall event with more Arctic air available in Canada. Canada finally getting getting colder

The EPS took a step toward the GEFS with the return of the Southeast Ridge by around January 20th. So we could see an end to this suppression pattern around then. Could also be our first 50° day since January 1st. New Euro run similar to GEFS Old run New GEFS run

I had an earlier post today which discussed NYC needing KU benchmark storms to reach average to above average seasonal snowfall. The one time this worked since 18-19 for NYC was 20-21 which was the only above average snowfall season last 6 years. So the frequent cutter, hugger, and suppressed Southern Stream storm tracks with the stronger Northern Stream of the Pacific Jet has been working against normal to above normal snowfall in NYC. All we know so far is that this has carried over into December and early January again this year. Too early to tell if it will continue beyond early January and into the next several winters. So we need to take it one step at a time. I am guessing this shift in the Pacific Jet is related to all the record marine heatwaves in the Pacific Basin which have appeared since 18-19. This faster Pacific Jet is also leading to changes in the 500mb patterns. Some of these changes have actually been to the benefit of the mid-Atlantic as we are seeing the next few days. Plus it’s easier for regions with traditionally lower average seasonal snowfall to get close to average with just one or two big snowstorms.

March 2013 to 2019 was the exception rather than the rule in NYC. Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Mean 8.4 8.4 2013 7.3 7.3 2014 0.1 0.1 2015 18.6 18.6 2016 0.9 0.9 2017 9.7 9.7 2018 11.6 11.6 2019 10.4 10.4 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Mean 0.1 0.1 2020 T T 2021 T T 2022 0.4 0.4 2023 0.1 0.1 2024 T T

We probably need to lose that low over the Rockies and Plains on the EPS and GEFS mean which is acting as a kicker to have a shot here.

I am more going by the last 60 years which is a large enough sample size to make a good analysis with. In the much colder climate from the 1960s to early 1990s NYC had 13 seasons within 5” of 25” inches. So the more stable colder climate had many seasons not far from average. With fewer well above and fewer well below snowfall seasons. Since 1994 all or nothing seasons with a larger range of above and below normal snowfall seasons have been the norm. With only 3 seasons near the 25” average and many more with larger + or - minus deviations from around 25”. This occurred against the background of the fastest warming 30 year period of modern times. So the amplitude of our snowfall range has increased. This new distribution pattern is also the same at surrounding stations like Islip. The last 6 seasons in NYC were 5 below and only one above. So the volatility since 1994 has been unchanged. 2010 to 2018 was our greatest concentration of all type seasons well above average. Very few normal seasons those years. So while I agree that 6 years is small sample size, we know with a high degree of certainty that NYC will need more coastal tracks as close to benchmark as possible to start getting more all type seasons again. In our warmer 2020s climate so far we have been seeing more cuttter, hugger, and suppressed southern stream systems. So unless we change this storm track pattern, the current average around 14” last 5 years will continue. I am going to let this winter which is the 6th play out before adding the data to the 2020s so far. But at least to date this season, we have seen the same storm track pattern. Hopefully, we can start to see some change from this next few weeks and beyond. So I am fairly sure in this all or nothing regime since 1994 that NYC will need to return to KU storm tracks soon to get the snowfall back over 20” before we finish the 2020s decade. Since it’s unlikely the colder climate of the 60s to early 90s will return with enough smaller to medium events to get close to average. In our much warmer climate NYC needs KUs for average to above average snowfall. Since we aren’t cold enough anymore to get to 25” with a bunch of smaller to medium events spread across a colder season from start to finish. It’s no coincidence that 2010 to 2018 featured the greatest concentration of KU events on record.

It’s was still cold enough back in the 1990s to have 2 seasons with 50”+ and a few seasons near the 25” average. These days 50”+ seasons are tough to come by with how warm it has been. Plus no seasons with near average 25”snowfall since 19-20. So our path to an decadal 25”snowfall average would be much narrower than the 1990s had to work with.

The one thing that is very unlikely is NYC returning to a 25” decadal snowfall average with a bunch of small to medium events. That was possible in a much colder climate era. The best shot of NYC getting back to around 25” for the 2020s are a return to big benchmark KU events.

NYC needs to shift the storm track back to benchmark KU events to get the decadal snowfall average over 20”. The first 5 years of the 2020s average of 14.2” is mainly the result of the dominant Northern Stream of the Pacific Jet. Plus the much warmer winters we have experiencing. So a continuation of the cutter, hugger, and suppressed Southern Stream isn’t going to get the job done. NYC was only able to get snowfall seasons above 20” without KUs when the climate was much colder. Since it was so cold that there were frequent enough nickel and dime events to break even. Since the 1990s its been all about KUs for average to above average snowfall. If we can shift the storm track back to benchmark this winter and the next 4, then we could get the snowfall back up above 20”. So here’s hoping that we can start seeing some benchmark tracks return the next several weeks. Monthly Total Snowfall for New York-Central Park Area, NY (ThreadEx) Click column heading to sort ascending, click again to sort descending. Mean 0.0 T 2.6 4.4 7.1 0.1 T 14.2 2023-2024 0.0 T T 2.3 5.2 T 0.0 7.5 2022-2023 0.0 0.0 T T 2.2 0.1 0.0 2.3 2021-2022 0.0 T 0.2 15.3 2.0 0.4 0.0 17.9 2020-2021 0.0 0.0 10.5 2.1 26.0 T 0.0 38.6 2019-2020 0.0 0.0 2.5 2.3 T T T 4.8

If we could only slow the NS enough so that GFS STJ streak could amp enough then maybe we could have some potential. But I would want to see agreement between the GFS, CMC, and Euro first. Don’t trust any individual OP runs beyond 120 hrs in this pattern.

Hopefully, we can reshuffle the Pacific deck of cards we have been playing enough in coming years for more STJ interactions. But it’s uncertain if that will be the case. Since in this new age of competing marine heatwaves the faster Northern Stream seems to be the default.

I think if the blocking was weaker with fewer shortwaves than we could have seen a cutter like the models had last weekend. The issue with this event was too many shortwaves in the fast flow with poor wave spacing. If we had a strong to record STJ like last February, then this -AO wouldn’t have been an issue.

The continuing overpowering Northern Stream of the Pacific Jet doesn’t have anything to do with luck as it’s a function of the pattern we have been in for years.

That area may also see the coldest temperatures next week due to the snow cover and great radiational cooling.

The coming cold departures won’t be that impressive for what is traditionally the coldest part of the year since Canada will be so warm.

What impressed me most about 95-96 was the extended cold and snow cover from late November into early April. It’s probably the closest that we have come to wall to wall cold and snow. 10-11 could have caught up and maybe surpassed it if the pattern didn’t shift after Janaury.

While it wasn’t as cold, it was snowier.

That was a really good one even though it didn’t have any lasting power. Extended record cold has been tough to come by over the last decade. Late December 2017 into early January 2018 was our last impressive winter Arctic outbreak lasting more than a few days. Data for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. 2017-12-27 24 17 -15.7 0.0 2017-12-28 18 11 -21.5 0.0 2017-12-29 22 11 -19.3 0.0 2017-12-30 23 17 -15.6 0.7 2017-12-31 21 9 -20.4 0.0 2018-01-01 19 7 -22.2 0.0 2018-01-02 26 13 -15.5 0.0 2018-01-03 30 16 -11.8 0.0 2018-01-04 29 19 -10.7 9.8 2018-01-05 19 9 -20.5 0.0 2018-01-06 13 6 -24.9 0.0 2018-01-07 18 5 -22.7 0.0 2018-01-08 31 17 -10.1 T

What I said in the post on December 20th that you just quoted was correct as we are dealing with the same fast Pacific flow. Heights are verifying lower over the EPAC and WNA than forecast. So not sure what the point is that you are trying to make. The current trough undercutting the weaker ridge than forecast out West is the reason the heaviest totals with storm are getting suppressed south. Faster flow and lower heights out west allow less shortwave spacing especially with a 50/50 low and confluence. EPS original forecast for this week from the December 20th post you quoted I was correct about the much weaker ridge and faster Pacific Jet undercutting the ridge

The ensembles contain a great deal of valuable information. It’s only the OP runs beyond 5-7 days which are causing the issue. Releasing an OP run through 0-168hrs along with the ensembles from 0 to 360 hrs would be the way to go. Plus the usual lower skill ensembles past 360hrs.

The 1980s were snowier than the first 5 years of the 2020s so far since they had a bunch of seasons near average. NYC only had 3 near average seasons since 1994 and none in the 2020s. During the 1980s more of the precipitation was falling as snow since it was much colder. Now the wetter winters than the 80s have a smaller percentage of the total precipitation falling as snow since it’s much warmer. Less precipitation and more snow during the 1980s. Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Mean T 0.1 2.3 7.9 5.4 3.0 1.0 19.7 1979-1980 T 0.0 3.5 2.0 2.7 4.6 T 12.8 1980-1981 0.0 T 2.8 8.0 T 8.6 0.0 19.4 1981-1982 0.0 0.0 2.1 11.8 0.4 0.7 9.6 24.6 1982-1983 0.0 0.0 3.0 1.9 21.5 T 0.8 27.2 1983-1984 0.0 T 1.6 11.7 0.2 11.9 0.0 25.4 1984-1985 0.0 T 5.5 8.4 10.0 0.2 T 24.1 1985-1986 0.0 T 0.9 2.2 9.9 T T 13.0 1986-1987 0.0 T 0.6 13.6 7.0 1.9 0.0 23.1 1987-1988 0.0 1.1 2.6 13.9 1.5 T 0.0 19.1 1988-1989 0.0 0.0 0.3 5.0 0.3 2.5 0.0 8.1 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Mean 0.0 T 2.6 4.4 7.1 0.1 T 14.2 2019-2020 0.0 0.0 2.5 2.3 T T T 4.8 2020-2021 0.0 0.0 10.5 2.1 26.0 T 0.0 38.6 2021-2022 0.0 T 0.2 15.3 2.0 0.4 0.0 17.9 2022-2023 0.0 0.0 T T 2.2 0.1 0.0 2.3 2023-2024 0.0 T T 2.3 5.2 T 0.0 7.5 Monthly Total Precipitation for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Mean 3.32 3.26 3.08 9.66 1979-1980 2.69 1.72 1.04 5.45 1980-1981 0.58 0.58 6.04 7.20 1981-1982 5.18 6.46 2.37 14.01 1982-1983 1.47 5.01 3.22 9.70 1983-1984 9.77 1.87 4.86 16.50 1984-1985 3.26 1.00 2.41 6.67 1985-1986 0.83 4.23 2.86 7.92 1986-1987 6.16 5.81 1.01 12.98 1987-1988 2.17 3.64 3.91 9.72 1988-1989 1.13 2.29 3.03 6.45 Monthly Total Precipitation for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Mean 5.13 3.64 2.85 11.61 2019-2020 7.09 1.93 2.54 11.56 2020-2021 4.61 2.31 5.13 12.05 2021-2022 1.39 4.29 3.23 8.91 2022-2023 5.83 4.38 1.28 11.49 2023-2024 6.71 5.28 2.05 14.04 Monthly Mean Avg Temperature for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Mean 38.0 31.2 35.4 34.9 1979-1980 41.1 33.7 31.4 35.4 1980-1981 32.4 26.2 39.3 32.6 1981-1982 36.5 26.1 35.3 32.6 1982-1983 42.7 34.5 36.4 37.9 1983-1984 35.2 29.9 40.6 35.2 1984-1985 43.7 28.8 36.6 36.4 1985-1986 34.2 34.1 31.9 33.4 1986-1987 39.0 32.3 33.2 34.8 1987-1988 39.5 29.5 34.9 34.6 1988-1989 35.9 37.4 34.5 35.9 Monthly Mean Avg Temperature for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Mean 40.9 36.9 38.6 38.8 2019-2020 38.3 39.1 40.1 39.2 2020-2021 39.2 34.8 34.2 36.1 2021-2022 43.8 30.3 37.3 37.1 2022-2023 38.5 43.5 41.1 41.0 2023-2024 44.6 37.0 40.1 40.6

We were able to get that one cold air drain down the Hudson Valley on December 22nd with the strong Arctic high and NNW flow missing the Great Lakes. Climatological Data for NY CITY CENTRAL PARK, NY - December 2024 Click column heading to sort ascending, click again to sort descending. Sum 1351 1020 - - 824 0 4.53 2.8 - Average 43.6 32.9 38.2 -0.9 - - - - 0.3 Normal 44.3 33.8 39.1 - 804 0 4.38 4.9 2024-12-01 38 27 32.5 -10.7 32 0 0.00 0.0 0 2024-12-02 39 29 34.0 -8.9 31 0 0.00 0.0 0 2024-12-03 42 32 37.0 -5.6 28 0 T T 0 2024-12-04 42 30 36.0 -6.3 29 0 0.01 T 0 2024-12-05 40 31 35.5 -6.5 29 0 0.09 T 0 2024-12-06 34 30 32.0 -9.7 33 0 0.00 0.0 0 2024-12-07 41 31 36.0 -5.4 29 0 0.00 0.0 0 2024-12-08 55 38 46.5 5.4 18 0 0.00 0.0 0 2024-12-09 51 44 47.5 6.6 17 0 0.18 0.0 0 2024-12-10 50 44 47.0 6.4 18 0 0.26 0.0 0 2024-12-11 60 41 50.5 10.2 14 0 0.85 0.0 0 2024-12-12 41 29 35.0 -5.0 30 0 0.00 0.0 0 2024-12-13 33 27 30.0 -9.7 35 0 0.00 0.0 0 2024-12-14 34 26 30.0 -9.5 35 0 0.00 0.0 0 2024-12-15 41 28 34.5 -4.7 30 0 0.06 0.0 0 2024-12-16 52 38 45.0 6.1 20 0 0.91 0.0 0 2024-12-17 59 49 54.0 15.4 11 0 0.02 0.0 0 2024-12-18 53 42 47.5 9.1 17 0 0.32 0.0 0 2024-12-19 45 37 41.0 2.9 24 0 0.05 0.0 0 2024-12-20 37 33 35.0 -2.9 30 0 0.04 T 0 2024-12-21 33 19 26.0 -11.6 39 0 0.15 1.8 2 2024-12-22 21 13 17.0 -20.4 48 0 0.00 0.0 1 2024-12-23 31 13 22.0 -15.1 43 0 0.00 0.0 1 2024-12-24 39 28 33.5 -3.4 31 0 0.10 1.0 1 2024-12-25 35 28 31.5 -5.2 33 0 0.00 0.0 1 2024-12-26 36 24 30.0 -6.4 35 0 0.00 0.0 1 2024-12-27 44 26 35.0 -1.2 30 0 0.00 0.0 1 2024-12-28 54 40 47.0 11.0 18 0 0.56 0.0 0 2024-12-29 60 50 55.0 19.2 10 0 0.16 0.0 0 2024-12-30 58 49 53.5 17.9 11 0 0.37 0.0 0 2024-12-31 53 44 48.5 13.1 16 0 0.40 0.0 0