bluewave

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

In great winter storm patterns over the years for our area, it wasn’t unusual for at least one of the long range model runs to correctly see the storm potential. During late January and early February 2021, it was an OP GEM run that had a correct KU forecast from a week out. With the poor storm track patterns for big snows since February 2022, none of those OP runs showing numerous KUs long range have verified.

I suspect that the issues the models have been having long range are related to the much faster Northern Stream of the Pacifc Jet which continues. It’s not typical to get a strong -WPO +EPO couplet at the the same time in December. So the shortwaves in the fast Pacific flow are lowering heights over Eastern Alaska while the -WPO ridge stands firm. At least into mid December the +EPO and stronger Pacific are trying to have the ridge roll out into the Plains while the -WPO would have the ridge axis more in the West. So a tug of war between two competing influences that we normally don’t see at the same time. My guess is that the ridge eventually comes east at some point during the 2nd half of December as the Pacific Jet eventually wins out in these situations. Notice how the 10 year December strong -WPO composite features a more -EPO and a relaxed Pacific Jet. Much stronger Pacific Jet and unusual +EPO in mid-December for a very strong -WPO block Past 10 strongest December 500 mb -WPO blocks didn’t have to compete with such a strong Pacific Jet and +EPO

Models usually don’t get exact timing for the relaxation of a pattern which has persisted for several weeks. This is why I have been using the general recent climatology in December. Every year since 2011 from Philly to NYC there was at least 1 day reaching 55 or greater from the 17th to the 25th. That period is still 9-17 days out which is beyond the reliable model skill. It doesn’t mean every day or even most days were this warm since 2011. Some years it was only a 1 day warm up with other years more than a day reaching these temperatures. But the general December patterns over the years which have had a cold December 1-16th had moderated in the departures from the 17th through the 31st. The degree of this moderation has also been variable.

Miss the 2010-2018 KU benchmark era when we could lock in a 168 hr euro control run showing a near 950 mb low close to the benchmark and have it be correct. https://www.weather.gov/okx/Blizzard_Jan42018

Better to rely on the the various ensemble means at this point which show a less amplified solution than the OP GFS due the fast flow and kicker lows coming into the West Coast at that time.

Occasionally, we do get a colder month across the CONUS. This is the first several weeks of colder conditions since January. But these colder periods have been few and far between. So they tend to stand out when they occur and get more attention than the persistent warmth which has become the new normal. I will update the chart below when December data gets posted.

30 years since the mid 90s and over 100 years prior to that period isn’t a small sample size. What you describe as rigid is actually a very comprehensive approach which I have used with great success for long range outlooks. Since my approach is data driven, I haven’t come to any firm ideas yet on whether we can eventually shift back to at least some occasional benchmark tracks in the future. But the long term decline in snowfall has been unmistakable. So I leave open the idea of a bounce off these lows in coming years if we can weaken the Pacific Jet a bit. But this is very uncertain since the recent shifts have been so extreme.

We haven’t had a single average or above average snowfall season since the mid 90s without having at least one NESIS 1 or higher BM KU snowstorm. So KU benchmark storms have been mandatory for reaching average to above average snow since 93-94. Prior to the mid 90s this wasn’t the case in the much colder climate. We could string together a series of smaller snow events and reach into the 20s for snowfall.

Fits the Great Lakes cutter, I-78 to I-84 hugger and Rain-snow gradient, and suppressed Southern stream which has dominated since 2018-2019. Very difficult to achieve a true benchmark KU track with such a fast Pacific Jet. Way too many issues with kicker lows, amplified ridges pushing the gradient just north of NYC, and generally very poor wavelength spacing with so many shortwaves racing through the fast flow.

Ski resorts continue to be the big winner the overpowering Northern Stream of the Pacific Jet.