bluewave

The warmer December than forecast allowed Lander, Wyoming to go +11.3° for December. The extreme winter warmth across parts of the CONUS regions has been unprecedented since 15-16. Before this period, having near to above a +10 monthly departure for a U.S. climate station would be a rare to uncommon event. We can remember the double digit departure months occurring much less frequently in the past. January 2006 in the Upper Midwest and March 2012 come to mind. Now these very high monthly winter departures have been happening yearly with multiple months in the same winter recording such departures. We have had a remarkable 12 winter months across varying ENSO states since December 2015 meeting this criteria for one or more climate stations. It’s even more impressive to see these monthly temperature departures occurring in the warmest climate normals period. Dec…2015….NYC….+13.3 JAN…2017….BTV…..+11.0 FEB….2017….ORD….+10.3 FEB…..2018…ATL….+10.6 FEB….2019…MGM….+10.5 JAN….2020…YAM….+9.8 DEC….2021….DFW….+13.2 JAN….2023….DXR….+12.3 FEB….2023…..SSI…..+9.8 DEC….2023….INL…..+15.8 FEB…..2024….FAR…..+17.5 DEC….2024…..LND…..+11.3

A neg nao would not be an issue with a great STJ pattern like we had in 2016 with the super El Niño. A La Niña dominant Northern Stream makes the 50/50 an issue. On top of the generalized faster Pacific Jet since 18-19.

Most of the time it’s cold enough to snow here in January. Some of our snowiest Januaries were warmer than average. But our big issue since the 18-19 has been the overpowering Northern Stream of the Pacific Jet. So it makes it harder to get heavy snows here with the cutter, hugger, and suppressed Southern Stream storm tracks. I would gladly take a warmer January like 2016 and 2017 if we had a primary benchmark storm track instead with the multiple KU events those years. Hopefully, we can get the fast Pacific flow with so many shortwaves close together to relax enough for at least one 4”+ or 6”+ event in NYC before the +PNA -AO eventually fades. But as we have seen even during some colder intervals this time of year there is no guarantee. Since the suppressed southern stream issue is showing up in the modeling wit the fast Pacific flow with multiple embedded shortwaves plus the 50/50 confluence. This is a situation where a dominant STJ would probably be of more benefit.

Same issue across North America and the entire Northern Hemisphere. https://www.star.nesdis.noaa.gov/smcd/emb/snow/HTML/snow_extent_monitor.html

Same situation as we have seen in recent years with the coldest departures going to our west or south. The delayed freeze-up on Hudson Bay and strong blocking there is keeping nearby Canada very mild. You can see the milder temperatures relative to the means working down into Northern Maine.

Yeah, this would have been a colder than average December in earlier decades since the average is close to 40° these days.

The record warm up near the end of the month dropped the monthly average departure to -0.5. EWR….-0.1 NYC….-1.2 JFK…..+0.9 LGA…-1.0 HPN….-0.3 BDR…..-1.3 ISP…..-0.6 AVG….-0.5

Happy New Year everyone. This was probably the most lightning we have ever seen to ring in the New Year. Very impressive light show here.

This was the lowest anomaly we have ever seen this time of year. The EPS weeklies missed this January pattern from back on December 11th. It had lower heights near Hudson Bay and Greenland and not the very strong blocking we have now. Almost looks like the original runs were defaulting to a coupled look with the strong SPV over Canada. Also notice the long range EPS continuing to show too strong a -EPO with lower heights near Alaska than originally forecast. Also a stronger Pacific Jet lowering heights near that region. https://nsidc.org/sea-ice-today/analyses/sluggish-freeze-warming-north https://sites.google.com/view/arctic-sea-ice/home/nsidc-arctic New forecast EPS forecast from December 11th

13-14 was more centered over the Midwest. 93-94 was one of the last times that Canada was able to load with so much Arctic air. Our best Arctic outbreak around NYC since 94 was during one of our warmest winters in 15-16 on Valentines Day. The key was the solid blocking north of Alaska. So NYC was able to go below 0° which it couldn’t pull off in the much colder 13-14 and 14-15 winters.

The Arctic outbreak in early January looks similar to other ones we have seen during the 2020s. The coldest departures relative to the means go to our west and south. Nearby Canada is still warmer than average with the delayed freeze- up around Hudson Bay. https://sites.google.com/view/arctic-sea-ice/home/nsidc-arctic

We are in track for the greatest AO volatility from October into January with possibly the first +4 October daily reading followed by -4 in January. https://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.ao.index.b500101.current.ascii

This could be one of our strongest January -AO patterns without a SSW .So maybe the delayed freeze-up around Hudson Bay is giving us an asssit. A very impressive bottom up rather than top down process.

The 7 station December average is currently at -0.9 which will be a little smaller after the 50° warmth today is factored in. EWR…-0.5 NYC….-1.3 JFK…..+0.6 LGA….-1.6 HPN….-0.8 BDR….-1.6 ISP…..-0.9 AVG….-0.9

With the forcing in multiple location on the VP anomalies charts, the early to mid January forecast isn’t the canonical MJO 8-2 where the coldest temperatures are usually found in the Northeast. This time the coldest temperatures will be displaced further to the south and west. Could also be related to the record low sea ice around Hudson Bay with the warmth there.

This may turn into a game of how much spacing we get between the individual shortwaves with so many systems in the fast Northern Stream flow and strong 50/50 low.

Even slightly colder Decembers like this one are still close to 40° around NYC since 2011. Monthly Mean Avg Temperature for LAGUARDIA AIRPORT, NY Click column heading to sort ascending, click again to sort descending. Mean 41.4 41.4 2024 38.6 38.6 2023 44.3 44.3 2022 38.7 38.7 2021 45.0 45.0 2020 40.9 40.9 2019 38.9 38.9 2018 40.5 40.5 2017 36.2 36.2 2016 40.3 40.3 2015 50.8 50.8 2014 40.6 40.6 2013 38.2 38.2 2012 42.7 42.7 2011 43.3 43.3

When you read the study they recently published they only mention some improvement day 3-5 over the NWP models. https://deepmind.google/discover/blog/gencast-predicts-weather-and-the-risks-of-extreme-conditions-with-sota-accuracy/ https://www.nature.com/articles/s41586-024-08252-9 The largest improvements of GenCast are often at shorter lead times up to around 3–5 days,

Boxing Day 2010 was the last time we saw a heavy snowstorm after December 20th. Part of the issue is that the 2nd half of December has been warming faster than the 1st half. The other challenge has been the lack of solid benchmark storm tracks this time of year. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending 12-21 ro 12-31 snowfall 2024-12-31 2.8 2 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 2010-12-31 20.0 0 2009-12-31 1.5 0 2008-12-31 0.5 0 2007-12-31 T 0 2006-12-31 0.0 0 2005-12-31 0.4 0 2004-12-31 2.4 0 2003-12-31 0.0 0 2002-12-31 5.0 0 2001-12-31 0.0 0 2000-12-31 12.8 0

The standalone AI models so far aren’t very good. We can remember the runs when they first launched a while back showing the hurricane going into New England. Then the system wound up curving well to the east. The one use of AI that may show some promise is using in a hybrid form where it corrects the NWP model biases.

I think the ultimate responsibility is on the modeling centers like ECMWF and NCEP for making operational model runs available beyond 120 to 168 hrs. We were joking a few months ago how extending the ECMWF OP to 360 hrs would go over. Once a product is out in the public domain there is nothing to stop someone from posting the image. We know that ensembles are the way to go beyond 120hrs to 168hrs and so do organizations like the NWS. Yet the modeling centers continue to run these OP runs out to 360 hrs and 384 hrs. It would be great if the only guidance products made available beyond 168hrs were the ensembles.

The one significant La Niña sign this December has been the much stronger than normal Northern Stream of the Pacific Jet. It lead to the ridge axis getting pushed further east than forecast with warmer temperatures than issued back on December 5th. Plus the dominant storm track through the Great Lakes was also classic La Niña. Very unusual to get such a strong Northern Stream with a +PNA. So even more of a La Niña mismatch December than we have seen on past occasions. Euro monthly forecast Verification

The mid 60s in NJ yesterday turned out to be a top 5 warmest for December 26th to 31st. Time Series Summary for NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending…warmest Dec 26th to 31st 1 1984-12-31 71 0 2 1982-12-31 68 0 3 2008-12-31 66 0 4 2024-12-31 65 2 5 1964-12-31 64 0 - 1936-12-31 64 0

We have had a dominant cutter, hugger, and suppression storm for most of the time since February 2022. So it may take some time to get a coastal track closer to the sweet spot for a 4”+ or 6”+ snow near NYC. You can see all 3 models with the windshield wiper effect from run to run the last 3 days. So it may just take some patience for something to click for us. Since there Northern Stream is still so active wave spacing and suppression could initially be an issue for us. I wouldn’t get invested on any individual system until 2-3 sets of models show it under 120 hrs. Plus we could always get a system that tracks too far north across the area and brings mixing issues near the coast if the vort ejecting from the West kicks up a transient ridge ahead of it.

The only thing I lean on is what I think the actual pattern will be. But colder patterns have been few and far between over the last decade. So it may seem to you that me reporting this is a bias. But it’s the actual pattern which has been biased warm. When we have had really cold patterns over this interval I was there.