December 2025 OBS and Discussion

[donsutherland1]

New York City finished December 1-10 with a mean temperature of 34.1F (1.2C). That was the coldest first 10 days of December since 2007 and sixth coldest since 2000.

A quick look at the guidance shows that a light snow event (probably 1"-3") across the New York City area is likely on Sunday. Given how snow events have been challenging to come by in recent years, to some it might seem like a big event. Even the previously bone-dry NBM shows 0.12" QPF. 

[bluewave]

7 hours ago, JerseyWx said:

People will say it's my "heat tolerance," but out my way I seldom use the AC in May and September, outside of short stretches.  In recent years we've even gone well into June without it.  Before we got that heatwave this past June in fact it was quite cool.  The city is outrageous with how it retains heat.  Sometimes I see they are close to 90 at midnight whereas I'll be in the mid 70's.

I grew up in Long Beach on the South Shore and we only needed the AC a handful of times back in the 1970s. First for the August 1973 heatwave and then the July 1977 heatwave. We gradually increased the AC usage during the 1980s and especially the early 1990s.

By the time we reached 2010, we had three ACs running much of the time compared to only one in the 1970s. Plus there was a rapid expansion of central AC even in Long Beach when it was a rarity near the shore in the 1970s. This is one of the reasons that HVAC is such a good career opportunity for people due to the increased demand in a warming world.

As for the UHI issue, there was a 10°+ difference between NYC during 1896 heatwave and the surrounding countryside. This mostly occurs with summer heatwaves where the city absorbs more heat during the day. It also occurs during calm and clear nights with radiational cooling.

The growth of skyscrapers in Western Brooklyn and Queens certainly changes the character of the neighborhood and of course you can see the change in the skyline since around 2004.

But prior to that that area had densely packed lower rise buildings built of bricks. These new high rises are mainly glass and steel which absorb significantly less solar energy than bricks do.

Plus a cluster of tall buildings will create a big area of shade which prevents the streets and sidewalks from absorbing as much heat as they did with smaller buildings with less shadows.

The warmest parts of NYC are in Queens near spots like Corona were small to medium size brick structures dominate. So changing from lower rise brick and concrete structures to skyscrapers may not change the UHI much in Western Brooklyn and Queens to really be noticeable to residents there. That’s why I said a drop in the bucket to what was already one of the largest UHI zones in North America.

The rural and suburban areas have warmed at a similar rate to places like Corona Queens over the years. So this is why both areas require more summer AC usage than they did during the 1970s.

My guess is that the higher dewpoints and maybe stronger winds are probably why a rural spot like the Charlotteburg Reservoir has seen a steeper increase in low temperatures than LGA since 1981.

[North and West]

I grew up in Long Beach on the South Shore and we only needed the AC a handful of times back in the 1970s. First for the August 1973 heatwave and then the July 1977 heatwave. We gradually increased the AC usage during the 1980s and especially the early 1990s.
By the time we reached 2010, we had three ACs running much of the time compared to only one in the 1970s. Plus there was a rapid expansion of central AC even in Long Beach when it was a rarity near the shore in the 1970s. This is one of the reasons that HVAC is such a good career opportunity for people due to the increased demand in a warming world.
As for the UHI issue, there was a 10°+ difference between NYC during 1896 heatwave and the surrounding countryside. This mostly occurs with summer heatwaves where the city absorbs more heat during the day. It also occurs during calm and clear nights with radiational cooling.
The growth of skyscrapers in Western Brooklyn and Queens certainly changes the character of the neighborhood and of course you can see the change in the skyline since around 2004.
But prior to that that area had densely packed lower rise buildings built of bricks. These new high rises are mainly glass and steel which absorb significantly less solar energy than bricks do.
Plus a cluster of tall buildings will create a big area of shade which prevents the streets and sidewalks from absorbing as much heat as they did with smaller buildings with less shadows.
The warmest parts of NYC are in Queens near spots like Corona were small to medium size brick structures dominate. So changing from lower rise brick and concrete structures to skyscrapers may not change the UHI much in Western Brooklyn and Queens to really be noticeable to residents there. That’s why I said a drop in the bucket to what was already one of the largest UHI zones in North America.
The rural and suburban areas have warmed at a similar rate to places like Corona Queens over the years. So this is why both areas require more summer AC usage than they did during the 1970s.
My guess is that the higher dewpoints and maybe stronger winds are probably why a rural spot like the Charlotteburg Reservoir has seen a steeper increase in low temperatures than LGA since 1981.

tl;dr it’s warmer now?


.

[WeatherGeek2025]

partly cloudy and cold here in White Plains. 29 degrees

[bluewave]

5 hours ago, donsutherland1 said:

New York City finished December 1-10 with a mean temperature of 34.1F (1.2C). That was the coldest first 10 days of December since 2007 and sixth coldest since 2000.

A quick look at the guidance shows that a light snow event (probably 1"-3") across the New York City area is likely on Sunday. Given how snow events have been challenging to come by in recent years, to some it might seem like a big event. Even the previously bone-dry NBM shows 0.12" QPF. 

It’s possible that some areas to our south with the strong cold departures through the 10th could finish December close to average with the coming warm up .

This also fits the pattern since at least the 1990s of the 2nd half of December warming at a faster rate than the 1st half in our area.