bluewave

Yeah, the surface 2mTs have been running warmer than the 850mb Ts due to the very low snow cover extent in NA, warmer Great Lakes, and Hudson Bay still not frozen over yet.

The sample size is reflective of our warmer modern climate. But it even worked most La Niña years during our colder climate from the 1950s to 1980s. My guess is the reason it has worked for over 50 years is that La Ninas still tend to be frontloaded by nature. So if the winter isn’t really big right out of the gates, then it’s tough to make it up on the back half which tends to be warmer and less snowy than the front half. The 83-84 and 84-85 winter were probably similar due to how cold that era was in the U.S. same for 71-72 and 73-74. But outside those years the relationship was pretty reliable. 88-89…Dec…0.3….season…8.1 85-86…Dec….0.9…season…13.0 84-85…Dec….5.5…season…24.1 83-84…Dec….1.6….season…25.4 75-76…Dec…..2.3…season…17.3 74-75…Dec…..0.1….season…13.0 73-74…Dec…..2.8…season….23.5 71-72…Dec……T……season….22.9 70-71…Dec……2.4…season….15.5 66-67…Dec…..9.1…..season….51.5 64-65….Dec….3.1…..season….24.4 55-56….Dec….3.3…..season….33.5 54-55….Dec….0.1……season….11.5 49-50….Dec…1.3…….season…14.0

NYC should see its first below 20° readings of season next few days that which is earlier than the 12-29 average first date of the last decade. Frost/Freeze 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 first below 20° temperature Minimum 01-20 (2024) 11-22 (2018) 286 Mean 02-18 12-29 310 2024 01-20 (2024) 18 - - - 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

We didn’t get the great December snowfall response around NYC Metro like we got from past +PNA La Ninas in December 1995, 2000, 2005, 2017, and 2020. The Pacific Jet was much stronger this time around and the Atlantic side blocking was also much weaker. So it was a warmer and less snowy outcome than those years. Hopefully, we can at least put together a 4”+ event in early to mid-January in NYC. I know people get excited when they see cold on the maps since it has been a rarity recently, but there are many that would rather have snow to go along with the cold. So cold temperatures plus snow would make many happy in early to mid-January.

Models have been underestimating the 500mb heights near Hudson Bay all month. So that open water could be playing a role. Notice how the biggest model error recently has been underestimating the forecast ridge there next week. Could approach record levels for this time of year. New run Old run Possible record 500mb heights for this time of year

The blocking with the record warmth around Hudson Bay has exceeded earlier model forecasts. Models are forecasting record 500 mb heights there later in the month. So plenty of easterly flow here last week of December with the warmer mins driving the late month departures.That ridge is the feature to watch into January as it could help NYC break its under 4” snowfall losing streak.

While the global temperatures have shown a slight cooling relative to past El Niños, the actual levels are still far beyond what has happened before the last few years.

While the actual SSTs have been on the weaker side until the recent drop, the atmospheric La Niña response through the EQSOI and OLR has been similar to much stronger La Ninas. https://www.climate.gov/news-features/blogs/enso/december-2024-enso-update-party-time-excellent

Many of the statistical relationships we find are just markers for underlying weather patterns that exist.

I don’t t think that’s how it actually works. December La Niña snowfall probably acts as more of a marker of what the pattern is able to produce. It’s not a December snowfall causing later seasonal snowfall relationship.That being said, we have still had some nice snowstorms following Decembers in NYC with under 3” back to 1991. Like in 99-00, 07-08, and 21-22. The one early snowfall indicator which has worked for every La Niña winter in NYC going back to the 95-96 has been the December La Niña snowfall. Years with 3 or more inches December have gone on to above normal seasonal snowfall. Every December with under 3” has had a below average snowfall season. This is why December is so important with La Ninas around NYC. 22-23….Dec snow…..T……season….2.3 21-22…..Dec snow….0.2…season…..17.9 20-21…..Dec snow….10.5…season…38.6 17-18……Dec snow….7.7…..season…40.9 16-17…….Dec snow…3.2…..season…30.2 11-12…….Dec snow….0…….season….7.4 10-11…….Dec snow….20.1….season….61.9 08-09…..Dec snow….6.0……season….27.6 07-08…..Dec snow…..2.9…..season….11.9 05-06…..Dec snow…..9.7…….season…40.0 00-01……Dec snow….13.4……season….35.0 99-00…..Dec snow…..T……….season….16.3 98-99…..Dec snow…..2.0……..season….12.7 95-96…..Dec snow…..11.5……..season….75.6

This winter will be a big win in my book if NYC can end the under 4” daily snowfall streak and not surpass 1932. Number of Consecutive Days Snowfall < 4 for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. 1 1394 1932-12-16 2 1063 1952-01-27 3 1056 2024-12-20 4 1051 1963-12-22

Hopefully, we can maximize any window we get in early to mid-January.

The biggest uncertainty going forward is how long we will be able to sustain the +PNA. Past December La Niña mismatches generally saw the +PNA reverse at some point in January. These were followed mostly by -PNA Februaries. But if there are other factors behind this +PNA that we haven’t detected, then not sure if we follow past events until we get more model data and verification further into the winter. The EPS weeklies are trying to show this shift in January. But not sure if they are just defaulting to La Niña climo. It’s possible that we still follow the La Niña progression even since this one was so weak. It will be interesting to see how things turn out.

January 2000 stands out as even more impressive a miss especially down in the Carolinas. Since many places that got the heavy snow didn’t even have a storm in the forecast the day before. I don’t think they ever figured out what happened with the models in that one.

Not really in terms of amounts since it was still within .2 spread. This happens all the time with rain. There is no way to narrow that margin down just because the precipitation is frozen rather than liquid. This was still good forecast. January 2015 was a significant model miss for snowfall here. Our greatest recent model error for snow was January 2000 when the storm was forecast to stay offshore and we got 6”+. They still may not know what lead to that model error. Back in the 1970s and 1980s it was more common for models to completely miss storm events. Jan 78 featured a NOAA weather radio forecast of rain heavy at times. Then the next morning we had 15” of snow on the ground. I believe February 1980 had forecasts for 3-6” and the storm missed to our south with nothing here. So while modeling has come a long way since then, a 0.2 error margin may be tough to overcome.

The difference between 0.1 and 2.0 is essentially noise as far as these models are concerned. All through the year we get rainfall events within this margin. But people only notice since it’s snow.

.5 of an inch here just east of HVN.

While it generally means below average seasonal snows, there have still been nice snowstorms following such Decembers. That’s why I am hoping we can maximize the potential January -AO +PNA window. We have seen decent snows following under 3” Decembers in January 2000 and February 2008 to name a few.

The most interesting model trend to me for early to mid-January isn’t the cold showing up, but the stronger blocking NE of Hudson Bay. This could be related to the delayed freeze up. As I have noticed heights beating guidance there all month in the extended forecasts. If we can get a +PNA and -AO at the same time, a place like NYC can see a 4”+ snow event with such a pattern. But there is still an issue of how broad the trough underneath will be. NYC has had issues with broad troughs from west to east across the CONUS in the past during cold patterns. We got a suppressed storm in Jan 19 which gave 12” to DC in a cold pattern with uppers lows in the SW and NE. But my hope is that a possible stronger -AO this time around could compensate and this January window can produce for areas that missed out over the last few winters. New run Old run

The most interesting part of the recent runs which may provide some snowfall hope in January is the much stronger blocking NE of Hudson Bay. This may be a feedback process related to the low sea ice. Chances would increase for a 4”+NYC event January 1-15 if we can get a +PNA and -AO at the same time. Even if we have to deal with a broad trough from the west to the east. New run Old run

Nice .25 of an inch coating here with very light snow falling.

Yeah, the 18-19 winter was when the Northern Stream of the Pacific Jet began to act as the spoiler. It was a great example of a January which averaged close to normal at 32.5° and only delivered a 1.0” snow squall for the month. The heaviest storm that month was a cutter with over 1.00” of rain around the 20th with highs around 60°. Then a strong Arctic outbreak later in the month with near 0° lows.

Steady light snow here with a light dusting on the colder surfaces and 33°.

Yeah, that was mid-January 2019 when they had the 12” snowstorm around DC which slid to our south. There was an upper low under the +PNA near the Southwest and one near the Northeast. The surface low couldn’t turn the corner up the coast due to the UL near the SW and east of New England. Data for January 12, 2019 through January 13, 2019 Click column heading to sort ascending, click again to sort descending. MD CLARKSBURG 2.1 NE CoCoRaHS 12.2 MD DAMASCUS 3 SSW COOP 11.8 MD ROCKVILLE 2.8 WNW CoCoRaHS 11.5 VA WASHINGTON DULLES INTL AP WBAN 10.6 VA WFO STERLING COOP 10.6 VA OAK HILL 0.3 WSW CoCoRaHS 10.5 VA WASHINGTON REAGAN NATIONAL AIRPORT WBAN 10.2

Almost looks like the super El Niño warmth being forecast for North America last week of December is a lingering effect from last winter but with a faster Northern Stream instead of the STJ due to the competing La Niña influences.