bluewave

Since 1995-1996 we have had 15 La Niña winters as defined by the RONI index. 14 out of 15 of those winters followed a repeating pattern which has been common the last 30 years. EWR, NYC, and LGA December snowfall pattern repeated throughout the entire winter. The Decembers with under 4” of snowfall at those stations went on to below average seasonal snowfall. With the Decembers over 4” or snow featuring average to naive average snowfall. You might ask how can this work out over 90% of the time? My guess is that La Ninas tend to show what they are capable of early on in the season. Plus as our climate has warmed it has lead to more repeating and persistent patterns. So I view this December to winter snowfall relationship more as a marker of a deeper underlying shared pattern rather than something that is directly causing the outcome. What is misleading about showing the long term snowfall trend in NYC since the regular observations began in the late 1800s? As the long term climate has warmed, the snowfall has gone down. There have been shorter term up trends like from the 80s to 10s against the long term decline. Plus snowfall measurements prior to the 1980s would be higher if measurements were taken as frequently as we do today.They also substituted melted down snow gauge measurements at times like in 1888 blizzard which undercounted the higher ratios back in the much colder era. So the actual downward trend line is steeper if we correct for the different way we measure snow now.

Exactly which part of the historic snowfall record do you disagree with?

In a warming climate we can get larger snowstorms which is what happened during 2010 to 2018. The main caveat was that we needed the dominant storm track to be colder to our southeast in order to realize the higher snowfall potential. With the northwest and warmer shift to the storm tracks since 2018-2019, we have resumed the long term downward trend in the snowfall setting all-time 7 year record lows for snowfall.

The Euro has been flip flopping from run to run with snowfall amounts on this one. Get it under 72hrs and have the same solution to be believable. We usually want at least 3 runs locking in to the same solution to have the model verify on snowfall.

Over 90% success rate for 14 out of the last 15 La Ninas spanning 30 years.

That standing wave is why I have been pointing out the warmer risks to the EPS extended forecasts after December 16th. Notice how the long range EPS missed the forcing there back in November. This is has been a regular EPS forecast error beyond 10 days in recent years due to the record marine heatwaves near the Maritime Continent. New run shows current MJO 4-6 standing wave Old run missed the current standing wave

We just have to be grateful for any snow we can get when the Pacific Jet is this extreme.

This is similar to what happened last year at this time with the models. Last December started with the extended guidance locking in the -EPO for the whole month. But as we approached the December 10th, the models caught onto how much stronger the Pacific Jet would be and the warmer +EPO pattern. Now the Pacific Jet is forecast to be much stronger mid-December than was indicated last week. Notice how much deeper the +EPO vortex is forecast to be now even with a near record -WPO 500 mb block. In the old days we would usually have the Pacific Jet weaken and we get more of a -WPO -EPO block. So we are on track for our annual warm up from December 17th to 25th. The +EPO is now forecast to becomes more dominant for our sensible weather than the -WPO as the Pacific Jet overpowers the pattern again. New run Old run

We haven’t had a December shoutout since 1895 when the first 15 days of the month were as cold as this year is going to be. Would be a new record for wasted December cold in the modern era. But nothing really surprises me anymore due to how extreme the Pacific Jet has become since 2018-2019.

With how hostile the Pacific has been, even a T to 2 would be a big win to avoid a shutout.

The most measurable snowfall in NYC in the post Boxing Day Blizzard era since 2011 has been between the December 11-20th. Time Series Summary for NY CITY CENTRAL PARK, NY 12-01 to 12-10 snowfall Click column heading to sort ascending, click again to sort descending. 2024-12-10 T 0 2023-12-10 T 0 2022-12-10 0.0 0 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 12-11 to 12-20 snowfall Click column heading to sort ascending, click again to sort descending. 2024-12-20 T 0 2023-12-20 0.0 0 2022-12-20 T 0 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 12-21 to 12-31 snowfall Click column heading to sort ascending, click again to sort descending. 2024-12-31 2.8 0 2023-12-31 0.0 0 2022-12-31 T 0 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

Hopefully, we can at least put a few inches on the ground while we still have the cold this weekend.

Models have a situational bias based on the specific weather regime. Long range models tend to underestimate the warmth in warmer patterns. None of the long range models saw the warmth in December 2015 from November forecasts. Same for the too numerous to count warmer periods since then. They also underestimate the cold from long range forecasts at times in the fewer colder patterns we get. As the recent November forecasts missed the first half of December cold. This was also the case before the transition to colder in 2014-2015. It’s just that the climate has become so skewed toward warmth, as Guy shows below, that there is much more opportunity to underestimate warmth than cold since it occurs so much more frequently.

They also got down to -22° on the 5th. It was there 2nd earliest behind 2019 for going under -20°. That station was only there since 1998. First <-20° Summary for SARANAC LAKE ADIRONDACK REGIONAL AP, NY Each section contains date and year of occurrence, value on that date. Click column heading to sort ascending, click again to sort descending. 2018 03-18 (2018) -22 11-23 (2018) -21 249 2025 03-03 (2025) -24 12-05 (2025) -22 276

First time since 2006 and 2008 that NYC dropped below 20° this early in the season. Central Park CLEAR 19 -1 41 CALM First low < 20° Summary for NY CITY CENTRAL PARK, NY Each section contains date and year of occurrence, value on that date. Click column heading to sort ascending, click again to sort descending. 2025 02-20 (2025) 18 12-09(2025) 19 - 2024 01-20 (2024) 18 12-21 (2024) 19 335 2023 02-04 (2023) 3 01-17 (2024) 17 346 2022 02-15 (2022) 16 12-23 (2022) 8 310 2021 02-08 (2021) 17 01-04 (2022) 19 329 2020 02-15 (2020) 14 01-29 (2021) 14 348 2019 03-07 (2019) 18 12-19 (2019) 16 286 2018 02-03 (2018) 16 11-22 (2018) 17 291 2017 03-12 (2017) 19 12-27 (2017) 17 289 2016 02-15 (2016) 13 12-15 (2016) 19 303 2015 03-07 (2015) 18 01-04 (2016) 14 302 2014 03-13 (2014) 18 01-06 (2015) 19 298 2013 02-18 (2013) 17 12-25 (2013) 19 309 2012 01-22 (2012) 18 01-22 (2013) 13 365 2011 02-22 (2011) 16 01-03 (2012) 15 314 2010 02-07 (2010) 17 12-14 (2010) 19 309 2009 03-04 (2009) 18 12-18 (2009) 16 288 2008 02-29 (2008) 17 12-08 (2008) 19 282 2007 03-09 (2007) 13 01-02 (2008) 17 298 2006 02-27 (2006) 18 12-08 (2006) 18 283