December 2025 OBS and Discussion

[Brian5671]

2 minutes ago, Krs4Lfe said:

Once the block hooks up with the southeast Ridge, like it’s been doing more often than not over the past few years that will keep most of the east US warm. The southeast Ridge is almost always under modeled so I’m not sure it’s a good look.

that would guarantee a couple of weeks of cutters too

[jm1220]

If we have a slightly negative or neutral PNA that would drive a more zonal jet stream, it could work with a -NAO, but a sharply negative -PNA would drive such a deep trough on the west coast that the SE ridge would respond and possibly link with the NAO block. That’s obviously what we want to avoid. 

[wxallannj]

5 hours ago, SACRUS said:

 

Through the 15th / first half of Dec Departure

LGA: -8.6
NYC: -8.6
EWR: -7.9
JFK: - 7.6

Saw that in NYC it was the coldest 15 days of December since 2005.

[Volcanic Winter]

1 hour ago, snowman19 said:

I wasn’t born yet lol but looking back on the weather history, the 1989-90 winter was probably (easily) the most extreme pattern flip we’ve seen in the last 50 years. We went from a record cold arctic tundra starting in November right through the end of December, then got a big cutter on New Year’s Eve and that was all she wrote, light switch flip to an unmitigated torch for all of January and February….

That’s really incredible. Weather and climatology are so fascinating to me, so many variables at any given time producing innumerable outcomes - sometimes resulting in extreme permutations.

I was born in the late 80’s so of course wasn’t around for the extremes of that decade. One of my first vivid weather memories however was the blizzard of 96… not a bad one to have. Was in Monmouth county for that as a kid. 

[snowman19]

21 minutes ago, jm1220 said:

If we have a slightly negative or neutral PNA that would drive a more zonal jet stream, it could work with a -NAO, but a sharply negative -PNA would drive such a deep trough on the west coast that the SE ridge would respond and possibly link with the NAO block. That’s obviously what we want to avoid. 

I believe @bluewave discussed the possibility of that happening (SE ridge hooking up with the -NAO) last week. A -PNA would definitely make that possibility more likely as you said

[EastonSN+]

10 minutes ago, snowman19 said:

I believe @bluewave discussed the possibility of that happening (SE ridge hooking up with the -NAO) last week. A -PNA would definitely make that possibility more likely as you said

Especially if the RNA is closer to the west coast and -2 or less.

Would not happen in a +PNA.

[Krs4Lfe]

28 minutes ago, EastonSN+ said:

Especially if the RNA is closer to the west coast and -2 or less.

Would not happen in a +PNA.

Yeah that's the benchmark to watch. If we see a deeply negative PNA, then rest of winter would probably be similar to winter 2023 and 2024. Big time snow and cold in the west, and warm and mild over here

[NEG NAO]

[North and West]

It was wild to say the least.    Most of the snow was suppressed south however.   Savannah, GA had a 10 inch snowstorm right before Xmas.   Around the 30th-it broke and never came back-Jan/Feb/Mar were absolute infernos

I remember being at my grandparents’ on New Year’s Eve and snow changing to rain. I then remember going to church in January in shorts, and then it snowed in early April.

Best part is that I got to do the weather report for my class the first week of December.

Wild second grade for sure.


.

[psv88]

36 today

[psv88]

Solar panels producing some power again today. Melt away

[qg_omega]

Weeklies are wall to wall warmth for January

[vegan_edible]

10 minutes ago, qg_omega said:

Weeklies are wall to wall warmth for January

everyone gets on snowman for being the debbie downer... but he has facts and stats to back his words up. 

 

i don't think i've seen you post one credible piece of info yet, and your call before thanksgiving led to one of the coldest starts to december we've seen in recent years. 

reverse psychology? old man yelling at cloud? just general dreadful demeanor so you can be a contrarian to what others on this board are hoping to see? 

whatever it is, it worked last time. so maybe this time, it will again:)

 

also. i've seen the weeklies. nothing is set in stone here...

[JenkinsJinkies]

5 minutes ago, vegan_edible said:

also. i've seen the weeklies. nothing is set in stone here...

It is also more than 2 weeks until the start of January.

[donsutherland1]

Temperatures will moderate for tomorrow through Friday. Thursday and Friday will be mild days with the mercury approaching or reaching 50° in parts of the region. A soaling rain is likely Thursday night and Friday. Much of the region could see a general 0.50"-1.50" of rain.

Behind the storm, the weekend will turn somewhat cooler. 

The probability that December 2025 will have a maximum monthly temperature below 60° is increasing. The last time that happened was in 2019 when the monthly high was 58°. If 2025 has a monthly high below 60°, that would be only the fifth such occurrence since 2000 (2003, 2004, 2005, and 2019 are the cases since 2000).

The ENSO Region 1+2 anomaly was -0.3°C and the Region 3.4 anomaly was -0.7°C for the week centered around December 10. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.33°C and the ENSO Region 3.4 anomaly has averaged -0.67°C. La Niña conditions will likely continue through at least mid-winter.

The SOI was -0.88 today. 

The preliminary Arctic Oscillation (AO) was +1.524 today. 

Based on sensitivity analysis applied to the latest guidance, there is an implied near 97% probability that New York City will have a cooler than normal December (1991-2020 normal). December will likely finish with a mean temperature near 34.3° (4.8° below normal). 

Supplemental Information: The projected mean would be 3.1° below the 1981-2010 normal monthly value. 

 

[Roger Smith]

Until you see a temp above 47 F, Dec 2025 remains tied with 1917 in first place for lowest max. Sadly that probably won't survive. 

Today's departure looks like it could push the running anomaly down to around -9 F which will perhaps be the low point for the month. As I was saying yesterday, lots of ups and downs ahead and I would expect this anomaly to be cut in half but -5 to -6 for the month is still possible if there's enough cold in the mix.  

If the mean after today drops to 32.4 F it will currently be tied with three t-28th coldest Decembers (for the entire month), a finish closer to 36 F seems likely, and the median of all 157 (if below 36.5) will be 36.5 F so there is some chance of the month being in the lower half of all Decembers, something that only happens two or three times a year in the modern and urban-warmed climate. 

A total of 26 Decembers had a mean at or below 32.0, the only recent ones being 1989 and 2000. By decades it is fairly easy to see the warming of the climate but about half of this is likely due to urban heat island increases. (27th was 1892 at 32.2 and the three at t-28th 32.4 are 1909, 1944 and 1995). Three more (1902, 1921, 1980) were tied at 32.5 F.

 

• DECEMBERS WITH MEANS 32.0 OR LOWER (listed by 30-year intervals slightly modified,

1869-1900 (8), 1901-30 (7), 1931-60 (6), 1961-90 (4), 1991-2024 (1).

1871 (29.2), 1872 (28.3), 1876 (24.9), 1880 (26.5), 1882 (30.6), 1883 (32.0), 1886 (29.6), 1890 (29.9)

1903 (31.5), 1904 (30.3), 1910 (30.0), 1914 (31.6), 1917 (25.0), 1919 (30.2), 1926 (28.9)

1935 (30.0), 1942 (31.1), 1945 (31.0), 1955 (29.7), 1958 (29.4), 1960 (30.9)

1962 (31.5), 1963 (31.2), 1976 (29.9), 1989 (25.9)

2000 (31.1)

 

[jetrz]

Today was the 20th consecutive day of below normal temperatures at Central Park. Anyone know where to find out how long its been since we've had such a streak?

[the_other_guy]

6 hours ago, Krs4Lfe said:

Yeah that's the benchmark to watch. If we see a deeply negative PNA, then rest of winter would probably be similar to winter 2023 and 2024. Big time snow and cold in the west, and warm and mild over here

That would be a mega flip. Out west is dying this year with low snow and AN.

 

Have we ever seen a winter with such a large flip like that for the whole country? It would be extraordinary