bluewave

The Euro seasonal tends to have more skill for its summer forecasts than during the winters. We have had several recent summer forecasts that did OK. But it doesn’t really do too well with the winter forecasts. Probably just too many interacting variables during the winter to figure out. The EPS skill level falls off markedly between week 1 and week 2 at most points during the year. Occasionally, it does very well week 3 and beyond like the forecasts for March 2012. Last winter the EPS exhibited several biases which it also has over the years. First, it completely missed the mid to late December EPO reversal from the forecasts near the start of December. I was pointing out early on how the Pacific Jet was being underestimated which turned out to be correct. So it had to play catch up with the big jet extension in mid to late December which lead to the warm up and strong +EPO vortex. Our recent pattern of the warm up between December 17th and 25th worked out like every December since 2011. During February I was pointing out early on that it was probably underestimating the Southeast ridge which is another bias. So the heavy snowfall axis it was forecasting closer to NYC wound up further north than earlier in the month. Toronto would up to be the big winner as we got our first February Southeast ridge link up with a 5 sigma Greenland block.

It’s an honest assessment and not a fatalistic one. When the WPAC is at record levels of warmth in the IOD tropical MC areas and midlatitudes east of Japan and to south of the Aleutians, it introduces warmer risks to the forecast. Both for warm MJO phases and a steeper temperature gradient between Asia and the Pacific. These two features lead to frequent jet extensions which send mild Pacific air into North America. This is why the snowfall season is starting out at record lows for North America. We will need some type of help like we got back in January 2022 to both weaken the Pacific Jet and allow at least a brief return to some benchmark tracks for maybe a month. At this point in the season it’s always a wait and see.

Very fast Pacific flow continues with storms racing through the Great Lakes. One of the storms next week will pull in a cooler airmass behind it lasting for several days. Doesn’t look too cold for this time of year as NYC may not be able to make it to freezing yet. Then a warm up after this as we rebound back to 60s and perhaps near 70° mid month. The Pacific Jet is so strong that ridge out West next week will eventually get pushed into the East after that. So a back and forth windy pattern. Most of North America will experience a milder Pacific influence. Snowcover for North America is starting the season at record low levels for this time of year.

The last big -IOD and rebound a few months later actually enhanced the storm track pattern back in late 2022 rather than changing it.

The key to NYC and nearby areas getting over 4” in December will continue to come down to the storm track. All the La Ninas in the last 30 years to go 4”+ in December had at least one snowy event with a stronger low tracking out near the benchmark. So we would want to start experiencing some deviation of this persistent Great Lakes cutter, I-78 to I-84 hugger, and suppressed Southern Stream storm track heading into December. But we haven’t had a storm track like this since January 2022. This fall so far has featured mostly Great Lakes cutters and huggers. The one coastal we got back in October was two weaker lows instead of one deep and consolidated low near the Benchmark. The Pacific Jet which has lead to this persistent pattern has been as strong as ever since October 1st. Maybe with some luck we can find a way to change up this storm track a bit at some point this winter or in coming winters. Not exactly sure what the catalyst for change would be since even an MJO 8 in March 2023 couldn’t even briefly shift the pattern. Very challenging with that record gradient between the Siberian cold and record WPAC SST warmth driving such a strong Pacific Jet.

12z guidance coming in more impressive and now has a narrow squall line with 50-60 mph gust potential along and just behind Wednesday evening.

The general rule around NYC Metro following SSWs that occur during any month of winter is that the snowfall is directly proportional to the amount that fell before the SSW occurred. So a winter with very little snowfall prior to the SSW usually won’t have a very snowy outcome after. Conversely, a snowy pattern before the SSW will usually become enhanced following the event.

I was talking mostly about snowfall which was lackluster those seasons following the SSWs. There wasn’t any cold to speak of in my area following the December 1998 event. While we did get some cold for around 10 days in January 1988, it wasn’t nearly as the cold as major January 1980s Arctic outbreaks were. 2001-2002 was essentially a year without a winter.

We haven’t had much luck with early SSWs since the late 1980s following December 2001, 1998, and 1987. https://csl.noaa.gov/groups/csl8/sswcompendium/majorevents.html

December 2021 had that big MJO 6-7 standing wave with drove the strong -PNA and the +13 around DFW. The most impressive 500 mb high latitude blocks over the last decade have been over the Kara and Barents seas areas. Could be some degree of feedback with the record low Arctic sea ice in that area.

From 2019 to 2025 with the lack of benchmark storm tracks ISP has only averaged 1.9” more than NYC with record 7 year lows for both sites at 16.8” and 14.9”. Since neither site does well with Great Lakes cutters, I-78 huggers, and suppressed Southern Stream storm tracks. During 2010 to 2019 ISP averaged 8.5” more than NYC since it was closer to all the benchmark storm tracks. It was the only 9 year period that ISP averaged near 50” a season. It was the golden age for benchmark KU storm tracks. From 1994 to 2009 ISP and NYC were also more evenly balanced around 28.0” a year since it was colder and we still had a good amount of benchmark storm tracks in the mix. During the colder era from 1964 to 1993, ISP averaged 25.8” a year vs 23.0” in NYC. So both ISP and NYC could average over 20” a year without having to exclusively rely on benchmark KU tracks. It was cold enough for hugger tracks to drop more on the front end before mixing or changeover. Plus we got more clippers dropping south of the area which have been lacking since then. Since 1993-1994 both ISP and NYC haven’t had over 20” without at least one benchmark KU snowstorm. Prior to 1993-1994 in the much colder climate we could get closer to average without a KU. Monthly Total Snowfall for ISLIP-LI MACARTHUR AP, NY Click column heading to sort ascending, click again to sort descending. Mean T 0.6 2.1 6.0 7.1 1.0 T 16.8 2024-2025 0.0 0.0 2.1 2.7 6.9 0.0 0.0 11.7 2023-2024 0.0 T T 3.1 7.8 0.0 0.0 10.9 2022-2023 0.0 0.0 0.4 T 3.0 1.6 0.0 5.0 2021-2022 0.0 T 0.3 31.8 3.3 1.6 0.0 37.0 2020-2021 T 0.0 7.5 1.1 24.9 T T 33.5 2019-2020 0.0 0.1 4.2 2.5 0.0 T T 6.8 2018-2019 0.0 4.3 T 0.9 3.5 4.1 T 12.8 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Mean 0.0 0.9 2.3 3.7 6.4 1.6 T 14.9 2024-2025 0.0 0.0 2.8 3.0 7.1 0.0 0.0 12.9 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 2018-2019 0.0 6.4 T 1.1 2.6 10.4 0.0 20.5 Monthly Total Snowfall for ISLIP-LI MACARTHUR AP, NY Click column heading to sort ascending, click again to sort descending. Mean 0.0 0.5 6.5 18.2 13.9 8.6 0.6 48.3 2017-2018 0.0 T 6.0 22.0 1.4 31.9 4.6 65.9 2016-2017 T T 3.2 14.0 14.7 7.4 T 39.3 2015-2016 0.0 0.0 T 24.8 13.2 3.2 0.2 41.4 2014-2015 0.0 T 0.4 30.2 13.4 19.7 0.0 63.7 2013-2014 0.0 0.3 8.1 25.2 24.5 5.4 0.2 63.7 2012-2013 0.0 4.2 0.6 3.3 31.4 7.4 0.0 46.9 2011-2012 0.3 0.0 T 3.8 0.6 T 0.0 4.7 2010-2011 0.0 T 14.9 34.4 3.9 2.1 T 55.3 2009-2010 0.0 0.0 25.3 6.4 21.7 0.4 0.0 53.8 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Mean 0.3 0.5 5.9 14.2 12.8 5.5 0.6 39.8 2017-2018 0.0 T 7.7 11.2 4.9 11.6 5.5 40.9 2016-2017 0.0 T 3.2 7.9 9.4 9.7 0.0 30.2 2015-2016 0.0 0.0 T 27.9 4.0 0.9 T 32.8 2014-2015 0.0 0.2 1.0 16.9 13.6 18.6 0.0 50.3 2013-2014 0.0 T 8.6 19.7 29.0 0.1 T 57.4 2012-2013 0.0 4.7 0.4 1.5 12.2 7.3 0.0 26.1 2011-2012 2.9 0.0 0.0 4.3 0.2 0.0 0.0 7.4 2010-2011 0.0 T 20.1 36.0 4.8 1.0 T 61.9 2009-2010 0.0 0.0 12.4 2.1 36.9 T 0.0 51.4 Monthly Total Snowfall for ISLIP-LI MACARTHUR AP, NY Click column heading to sort ascending, click again to sort descending. Mean T 0.3 5.8 7.1 8.7 5.3 1.0 28.3 2008-2009 0.0 T 10.4 8.9 3.3 13.6 T 36.2 2007-2008 0.0 0.0 2.6 0.8 7.3 T 0.0 10.7 2006-2007 0.0 T 0.0 1.0 4.2 3.8 T 9.0 2005-2006 0.0 0.5 7.6 4.7 19.9 3.2 0.1 36.0 2004-2005 0.0 T 7.0 21.5 17.0 13.3 0.0 58.8 2003-2004 0.0 0.0 15.5 19.1 1.1 5.7 0.0 41.4 2002-2003 0.0 1.0 16.0 2.6 26.3 3.7 5.0 54.6 2001-2002 0.0 0.0 0.0 3.7 T T 0.0 3.7 2000-2001 T 0.0 10.8 9.2 8.6 10.3 T 38.9 1999-2000 0.0 T 0.4 5.8 2.6 0.2 T 9.0 1998-1999 0.0 0.0 3.0 4.5 2.8 9.1 T 19.4 1997-1998 0.0 T 1.0 T T 1.6 T 2.6 1996-1997 0.0 T 1.2 3.3 2.2 3.7 2.0 12.4 1995-1996 0.0 3.0 13.3 20.2 19.0 12.0 9.6 77.1 1994-1995 0.0 T T T 5.1 T 0.0 5.1 1993-1994 0.0 T 3.3 8.8 20.0 5.0 0.0 37.1 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Mean T 0.2 5.4 7.5 10.4 4.2 0.4 28.0 2008-2009 0.0 T 6.0 9.0 4.3 8.3 T 27.6 2007-2008 0.0 T 2.9 T 9.0 T 0.0 11.9 2006-2007 0.0 0.0 0.0 2.6 3.8 6.0 T 12.4 2005-2006 0.0 T 9.7 2.0 26.9 1.3 0.1 40.0 2004-2005 0.0 T 3.0 15.3 15.8 6.9 0.0 41.0 2003-2004 0.0 0.0 19.8 17.3 0.7 4.8 0.0 42.6 2002-2003 T T 11.0 4.7 26.1 3.5 4.0 49.3 2001-2002 0.0 0.0 T 3.5 T T T 3.5 2000-2001 T 0.0 13.4 8.3 9.5 3.8 0.0 35.0 1999-2000 0.0 0.0 T 9.5 5.2 0.4 1.2 16.3 1998-1999 0.0 0.0 2.0 4.5 1.7 4.5 0.0 12.7 1997-1998 0.0 T T 0.5 0.0 5.0 0.0 5.5 1996-1997 0.0 0.1 T 4.4 3.8 1.7 T 10.0 1995-1996 0.0 2.9 11.5 26.1 21.2 13.2 0.7 75.6 1994-1995 0.0 T T 0.2 11.6 T T 11.8 1993-1994 0.0 T 6.9 12.0 26.4 8.1 0.0 53.4

It’s been a challenge maintaining strong enough 500mb blocking across the WPO, EPO, PNA, and TNH regions. The last time we pulled this feat off was January 2022. Last winter the block kept getting undercut and eroded from the very fast Pacific Jet sending shortwaves through. So this continued the Great Lakes cutter, I-78 to I-84 hugger, and suppressed Southern Stream storm tracks.

I am going weaker on the PNA than last winter. But there could still be +PNA intervals. Very strong warmth and 500mb ridging in Canada since May 2023.

It’s based in the peak MJO 5 phase in October. Since the MJO weakened into phase 5 after moving through phase 4. But even if that 2.42 made it into 5, then it would still be lower than the 2.76 to 3.35 of the mismatch years.

Weaker MJO 5 peak this October similar to the non PNA mismatch years like 2022, 2021, and 2016. I was expecting this since we haven’t had two back to back La Niña PNA mismatch winters before. So a milder signal for temperatures than last winter. Could still be some +PNA intervals just weaker than we had last winter. http://www.bom.gov.au/clim_data/IDCKGEM000/rmm.74toRealtime.txt October 2025….Phase 5 peak +1.302… October 2024….Phase 5 peak +2.762…ONI….latest weekly only -0.3 October 2022…Phase 6 peak +2.177…..ONI….-1.0 October 2021….Phase 5 peak +2.087….ONI….-1.0 October 2020…Phase 5 peak +2.818….ONI…..-1.3 October 2017….Phase 6 peak +3.353….ONI….-1.0 October 2016….Phase 5 peak +1.800….ONI….-0.7