bluewave

First December for NYC with 10”+ of snow and a 60°Christmas. It was also the first 7 year period with 3 years reaching 60° or warmer on Christmas. Data for December 25 - NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Date Max Temperature Min Temperature Precipitation Dec Snowfall 2015-12-25 66 57 0.01 T 1982-12-25 64 41 0.02 3.0 1889-12-25 64 43 0.00 6.0 2014-12-25 62 44 0.09 1.0 1940-12-25 62 38 0.00 3.0 1979-12-25 61 50 0.87 3.5 2020-12-25 61 10.5 1964-12-25 60 49 T 3.1

It helped having the 4 coldest days of the month follow the snowstorm.

The oddity this month for NYC is how mild it has been for a December with a 10”+ snowstorm. Most other Decembers were much colder. But warm and snowy has been a new theme that has emerged since the mid 2000’s. 2020...39.3...so far 2010...32.8 2009...35.9 2003...37.6 2000...31.1 1960...30.9 1948...38.3 1947...34.0 1933....32.7 1916....34.0 1912....39.3 1872....26.7

The south based blocking has been a theme this month. Notice the warmer than normal temperatures pushing down into the Northeast. This may be related to the record SSTs over the NW Atlantic and cold pool south of Iceland.

We only needed one storm this month for many areas to get to above normal snowfall. That was when the +PNA combined with the -AO-NAO. It really came down to that supercharged 50/50 low we got. Otherwise, the tucked in storm on the 16-17th would have been a warmer event. As it was my area only got 4” of snow due to the WAA aloft and quick flip to sleet. The month will end milder than models were expecting just several days ago. You mentioned the trade wind surge a few days ago. That may be related to why we are getting the Niña ridge showing up north of Hawaii. But this is still occurring with other more Niño-like features. We would definitely need more help from the PNA in January to counter the +EPO and fast Pacific Jet. But those short term details usually don’t show up on the longer range forecasts. Just a little +PNA can go a long way with -AO -NAO. Slight Niña Ridge poking up north of Hawaii allowing more of a trough out West

That’s why we have to wait for the individual short waves. We will definitely need help from the PNA with such a strong PAC Jet and +EPO. But models won’t show those fine details until we get within about a week of the actual forecast period.

Clash of the Titans pattern on the EPS 11-15 day mean. Firehose Pacific Jet vs one of the strongest -NAO -AO blocks that we have seen in early January. We need to get a nice retrogression of the Greenland block back toward the PNA region. A small +PNA rise can go a long way with a North Atlantic look like that. So some interesting tracking coming up in January when the individual short waves come into better focus.

South Florida and New England will have similar temperatures for a time Christmas morning.

We just need the trough out West to shift east under the block after New Years. But you can see how the models are showing more ridge in the East now than 3 days ago to close out the year. The wave break and record block south of Greenland is too south based next week with no room for cold 50/50 low pattern. New run Old run

The block starts out too far south next week on the latest EPS. So the EPS doesn’t leave room for a cold 50/50 low pattern. It looks like milder temperatures this run in the 6-10 day period.

The warming state of the planet has been the ultimate competing influence.

We started to see these ENSO disconnects when the 15-16 super El Niño California rainfall got delayed into the 16-17 La Niña. Then it was off to the races when the El Niño didn’t couple in 18-19. Last winter we saw weak El Niño conditions produce an 11-12 style La Niña pattern. So it’s no surprise we are getting an El Niño-like pattern with a moderate La Niña.

We have seen these strong trade wind surges and Niño 3.4 dipping temperatures back to the fall. All the competing influences have resulted in a more Niño-like pattern. Notice how the PNA is forecast to stay positive right into January. Beyond early January, it will be interesting to see which type ENSO pattern prevails.

Another El Niño-like feature that we are experiencing this month is the mild average temperature combined with the 10”+ snow in NYC . Since 1995 , all the 35.9° or warmer Decembers with 10”+ were warmer ENSO years. The snowy La Niña Decembers all had a monthly average around 32° degrees. This month is already 39.1° before the big coming solstice warm up. An interesting question to ask is how long can we keep this Niño-like pattern going? I looks like January will at least start out more Niño-like. So it will be interesting to see which ENSO type pattern shows up in February. Warmest Decembers highlighted...NYC snowfall....average temperature....Niño 3.4 temperature.... Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Dec Click column heading to sort ascending, click again to sort descending. Rank Year Total Snowfall Temp/ Niño 3.4 1 2010 20.1 32.8/-1.6 2 2003 19.8 37.6/+0.4 3 2000 13.4 31.1/-0.7 4 2009 12.4 35.9/+1.6 5 1995 11.5 32.4/-1.0 6 2002 11.0 36.0/+1.1 7 2020 10.5 39.1/-1.2

NYC is on track for its first Christmas with a morning high of 55-60 and an evening low in the 20s. Our new era of big temperature swings continues. The previous coldest temperature on Christmas with such a warm high was 33° in 2008. Data for December 25 - NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Date Max Temperature Min Temperature Precipitation Snowfall Snow Depth 2015-12-25 66 57 0.01 0.0 0 1982-12-25 64 41 0.02 0.0 0 1889-12-25 64 43 0.00 0.0 M 2014-12-25 62 44 0.09 0.0 0 1940-12-25 62 38 0.00 0.0 0 1979-12-25 61 50 0.87 0.0 0 1964-12-25 60 49 T 0.0 0 1994-12-25 59 41 T 0.0 0 1965-12-25 59 47 0.65 0.0 0 1932-12-25 59 47 0.13 0.0 0 1893-12-25 58 45 0.00 0.0 M 2008-12-25 57 33 0.13 0.0 0 1936-12-25 56 40 0.00 0.0 0 1933-12-25 55 34 0.00 0.0 0 1915-12-25 55 38 0.01 0.0 0

Yeah, this month looks like a continuation of the atmospheric coupling weirdness of recent years. The 500 mb pattern is much more El Niño-like. Especially the deep Aleutian Low and +PNA. I guess that this makes up for the last 2 winters which were technically El Niño with La Niña-like 500 mb patterns.

The Euro has one of the strongest south based blocks that we have seen this time of year. It has a whopping +6 SD 500 mb height anomaly just south of Greenland. A 584 dm ridge east of Newfoundland should be very close to the record in late December.

The timing of the Christmas cold front looks to be early Christmas morning. The EURO and new GFS V16 are pretty close. So the high for the day will be early with falling temperatures after. Another big temperature swing weather pattern.

Yeah, having a much warmer than average NW Atlantic nearby makes a big difference. ISP has had 5 events of 17” or greater since the 09-10 winter. MSP recorded one 17” snowstorm over the same period. for ISLIP-LI MACARTHUR AP, NY 27.8 2013-02-09 24.9 2015-01-27 23.9 2009-12-20 23.7 2016-01-24 18.4 2018-03-22 for Minneapolis-St Paul Area, MN (ThreadEx) 17.3 2010-12-11

The Christmas storm wave break looks like it may be off the charts. The ridge just south of Greenland goes more than +5 SD. This could be one the strongest blocks in that region for this time of year. So we will be probably be looking at winter storm threats from the end of December right into January.

Moving into our annual solstice warm up this week. Followed by a return to cooler than normal after Christmas. The Southeast will turn out to be the coldest part of the CONUS relative to the means this month. Florida is on track for their first colder than average month since March 2018.

I guess that he only ran the model for that storm. But it’s also happening in places like Japan. https://www.washingtonpost.com/weather/2020/12/18/japan-snow-stranded-motorists/

The WAA aloft and dryslot did their thing.

I only got 4” here before the sleet arrived. So the bar is set pretty low. I will go out on a limb say that there will be a better storm than that at some point this winter.

The Christmas storm looks to really create a major wave breaking event. So I am taking a wait and see approach as to how long after that we can expect a colder and snowier storm track. I am hoping that we can finally get a cold enough storm for the South Shore to finally get into the jackpot zone like we were in 15-16, 16-17, and 17-18.