Snow Potential Dec 26-27

[steve392]

Had heavy sleet turn back to big flake snow then back to sleet then snow again.  Up in Dumont, nj and it's plain snow. 

[The 4 Seasons]

Looks like OKX/PHI cut back on amounts and downgraded warnings to advisories for Somerset and Middlesex. Saw that coming, glad we went conservative there

[steve392]

Heavy heavy snows in Dumont, nj right now.  Really accumulating.  Salting isn't going to do anything now. 

[DDweatherman]

On 12/25/2025 at 4:33 PM, PhiEaglesfan712 said:

That has no correlation. NYC cashing in on a snowstorm doesn't mean everyone is going to win come January. For all we know, DC could end up with a final season snow total of 3-4" (see below).

That season had one of the oddest snow distributions ever. Places in upstate NY finished the season with over 150 inches of snow, while places like Baltimore and DC finished with less than 4 inches of snow.

I’m late on my reply. I meant that in no meteorological way. It was really just supporting my northern brethren in hopes that we get a miller A or a big hybrid low that blesses the masses later this winter!

[TriPol]

Winter Storm Warnings are canceled for the immediate Metro area. 

[donsutherland1]

17 hours ago, donsutherland1 said:

I'll do the 18z HRRR, too. I think that model is often cold-biased, but let's see how it does.

18z HRRR.

I will also compare the 18z NAM and 18z HRRR.

My point estimates:

Bridgeport: 8.0"
Islip: 7.9"
New York City (Central Park): 5.8"
Newark: 4.8"

18z NAM vs. 18z HRRR: 

Here's how I fared against the two models:

Final Accumulations:

Bridgeport: 7.1"
Islip: 6.6"
New York City-Central Park: 4.3"
New York City-JFK Airport: 4.1"
New York City-LaGuardia Airport: 4.1"
Newark: 4.2"

The low end of the 4"-8" idea worked out. The loss of precipitation from the weak lift that developed in the spacing between the surface and mid-level low likely deprived the region of several inches of snow. It also allowed for some intrusion of sleet into the greater New York City area for a time until the lift improved.

[EastonSN+]

9 minutes ago, donsutherland1 said:

18z NAM vs. 18z HRRR: 

Here's how I fared against the two models:

Final Accumulations:

Bridgeport: 7.1"
Islip: 6.6"
New York City-Central Park: 4.3"
New York City-JFK Airport: 4.1"
New York City-LaGuardia Airport: 4.1"
Newark: 4.2"

The low end of the 4"-8" idea worked out. The loss of precipitation from the weak lift that developed in the spacing between the surface and mid-level lows likely deprived the region of several inches of snow. It also allowed for some intrusion of sleet into the greater New York City area for a time until the lift improved.

You nailed this one Don. Great job!

[BxEngine]

24 minutes ago, donsutherland1 said:

18z NAM vs. 18z HRRR: 

Here's how I fared against the two models:

Final Accumulations:

Bridgeport: 7.1"
Islip: 6.6"
New York City-Central Park: 4.3"
New York City-JFK Airport: 4.1"
New York City-LaGuardia Airport: 4.1"
Newark: 4.2"

The low end of the 4"-8" idea worked out. The loss of precipitation from the weak lift that developed in the spacing between the surface and mid-level lows likely deprived the region of several inches of snow. It also allowed for some intrusion of sleet into the greater New York City area for a time until the lift improved.

This is kind of awesome to see, thank you for doing that work!

[SnoSki14]

So the no 4" streak is officially over then 

[donsutherland1]

Just now, SnoSki14 said:

So the no 4" streak is officially over then 

For snowstorms, it's over. Finally. For daily snowfalls, it, unfortunately, continues.

[donsutherland1]

As forecasting accuracy requires, among other things, an objective assessment of the guidance, I've expanded the comparison of the 12/26 18z NAM and 12/26 18z HRRR. The major point of contention had been whether the NAM was providing a realistic forecast for the New York City area. It did not fare well.

But what over a larger area? Again, the HRRR outperformed the NAM, but its forecasting edge was less decisive. The HRRR was better in assessing where the 4" or above snows would fall from New York City southward. The NAM confined such snows to the north and east of New York City. However, the HRRR was too aggressive in pushing 2"+ snows past Allentown and into Philadelphia. The HRRR also did better in such locations as Albany and Boston.

12/26 18z NAM:

12/26 18z HRRR:

Outcomes for 12 Cities:

[qg_omega]

23 hours ago, donsutherland1 said:

For fun, let's compare the 18z NAM with the NWS for select locations that provide snowfall reports:

18z NAM:

NWS Forecast:

I will be looking at the other 18z guidance. For now, I still think a general 4"-8" snowfall is likely in and around New York City (including all of the above locations).

Verification scores?

[donsutherland1]

31 minutes ago, qg_omega said:

Verification scores?

Against the NWS? I will run them when I get back in this evening. This wasn’t the NWS’s finest forecast.

[eduggs]

12 minutes ago, donsutherland1 said:

Against the NWS? I will run them when I get back in this evening. This wasn’t the NWS’s finest forecast.

Couple minor comments: on the 18z NAM snowfall map I looked at on pivotal at 10:1, Islip was 5.0, NYC was 2.6, and Newark was 0.8. But the colored graphics look wonky - I'm not sure how accurate they are. Point and click shows about 2" for Newark. It shouldn't be much different than MMU considering their relative lat lon positions.

Secondly, I don't believe those numbers count sleet. I believe the algorithm ignores accumulated sleet and only displays the snow equivalent. So some sleet accumulation (NYC and EWR) would lead to underestimation.

Since snow accumulation is a very inexact metric to both forecast and measure, I don't believe a subset of reported snow totals is a good method to assess model verification.

[eduggs]

Middletown is a funny case. For the Tue event the NWS hoisted a last minute WAA and the area ended up with warning snows. For this relatively long lead WSW event, I believe that area ended up in the upper tier of advisory snows. Snow is very difficult to accurately predict.