Extreme Cold, Snow & Sleet: SECS 1/25 - 1/26

[donsutherland1]

On a more serious note regarding the NAM, the RGEM's high-resolution model and most of the global models use 4dVAR (four-dimensional variation) initialization. The NAM uses the older 3dVAR (three-dimensional variation) initialization. The general idea of warmer air moving in to change the snow to sleet in coastal areas and the New York City area and its nearby suburbs is the baseline idea due to lots of support. It's uncertain whether the NAM is overdoing things on account of its older initialization scheme or if it sees something the other guidance doesn't. If it begins to adjust late today (18z or later), that could be an indication that the older initialization process was playing a role. If, on the other hand, the other guidance starts shifting, that will indicate that the NAM, despite its limitations, had correctly resolved some of the details ahead of the other guidance.

[Prue11]

2 minutes ago, Winterweatherlover said:

If the NAM is right just hope it's sleet and not ZR.

I really doubt we see zr in the nyc area. 

[weatherpruf]

2 minutes ago, Prue11 said:

Dude have some positivity you’re posting nothing but negative thoughts for our area. Maybe we’ll bust in a positive way, not likely but you never know

the poster knows his stuff. and he has seen this before many times, so have i. i have been saying the ceiling around here has been about 6 in my lifetime for these kinds of events, however, nws seems convinced a wall of heavy snow is coming first, making this one different. i have seen a foot of snow pile up really fast a few times, jan 1987 comes to mind, a disaster on a weekday no one was ready for. hand over my heart i expect 5-6 out of this out here, but won't discount experts who think it could be more.

[Winterweatherlover]

1 minute ago, MJO812 said:

Agree

Fv3 is all snow and a big thump 

I think the all snow idea is pretty much done, it's not realistic with this storm but hopefully it comes in very thumpy.

[MJO812]

Just now, Winterweatherlover said:

I think the all snow idea is pretty much done, it's not realistic with this storm but hopefully it comes in very thumpy.

Yep have to hope. 

[Jt17]

Agree
Fv3 is all snow and a big thump 

Can somebody post F27 from Fv3 vs. NAM. It's a wild difference.


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[The 4 Seasons]

2nd update and likely final call. We split up the initial range of 8-16" to 8-12" and 12-16". Think the city and LI fit well within 8-12", dont see them getting over a foot despite what the NWS thinks. Some reasons behind this conservative call:

• Though a lot of qpf falls as snow, many models bring significant warming H7-H8 during the height/back end of storm
• Ratios on BUFKIT look initially high for many areas but fall to around 10:1 or in some cases a bit lower, went a bit above 10:1 for average
• Excellent frontogensis will produce rates of 1-3" per hour for a while then move N/NE of the area
• Went with a blended approach mainly GFS/EC/Canadian and threw out warm outliers, NAM not used.
• 8-12" amounts most common with 12"+ well N/W of the city but think around 16 is the cap
• Dry air moves in and shuts off pcp any redeveloping snows will likely be N of MA boarder/dutchess/ulster after midnight/early monday

If any significant changes happen today well do an update before the storm as we still about 24hrs out. 

 

[jm1220]

Just now, kat5hurricane said:

SWFEs usually underperform here at the coast, I never get excited about them. We just better hope that the thump is going to be very heavy because the changeover time seems to get sped up with every set of runs.

Yep, it really comes down to the radar presentation in the morning and nature of what's coming at us. I think the fundamentals of the storm are decided-it's a SWFE although much bigger and higher impact nationwide than usual, and there won't be redevelopment in time to stop warm mid level air enough for sleet from getting to 70-80% of us. This isn't one of our heavy snow setups for NYC-we're relying on a huge high pressure dome to provide overrunning and retreating confluence to provide some resistance but those won't be enough. We're making the best hopefully of a lousy storm setup for us in general. If we can make the most of the remaining mid level cold air with heavy steady snow we can get a higher end outcome like the HRRR or hi res RGEM. If it comes in like shredded garbage we'll end up with something like the NAM because all this moisture also will advance the warm air like gangbusters. Whether we like it or not or "vibes we give it" is irrelevant, it's just reality. In the January thread some are pointing out how the pattern should change to one that is more favorable for heavy snow in NYC and we will have cold around for quite some time so even if this one joins the long list of SWFE suckfests, there should be more opportunity and what we get will last for a long time. 

[mriceyman]

NAM also showing that sleet line crashing south again and then back north in the evening. Somewhere along that area is in for a rough few hours.

I think us in monmouth are gona be in the battle zone


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[mriceyman]

Nam and euro basically showing same thing just the Nam has sleet line here by 1 versus euro which is 4? 

3 hours is a big difference


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[Winterweatherlover]

1 minute ago, jm1220 said:

Yep, it really comes down to the radar presentation in the morning and nature of what's coming at us. I think the fundamentals of the storm are decided-it's a SWFE although much bigger and higher impact nationwide than usual, and there won't be redevelopment in time to stop warm mid level air enough for sleet from getting to 70-80% of us. This isn't one of our heavy snow setups for NYC-we're relying on a huge high pressure dome to provide overrunning and retreating confluence to provide some resistance but those won't be enough. We're making the best hopefully of a lousy storm setup for us in general. If we can make the most of the remaining mid level cold air with heavy steady snow we can get a higher end outcome like the HRRR or hi res RGEM. If it comes in like shredded garbage we'll end up with something like the NAM because all this moisture also will advance the warm air like gangbusters. Whether we like it or not or "vibes we give it" is irrelevant, it's just reality. In the January thread some are pointing out how the pattern should change to one that is more favorable for heavy snow in NYC and we will have cold around for quite some time so even if this one joins the long list of SWFE suckfests, there should be more opportunity and what we get will last for a long time. 

Are there key locations in the south that we should be checking in terms of NAM predictions vs actual outcomes?

[nycsnow]

Just now, mriceyman said:

3 hours is a big difference


.

Literally can be 3-6 inch difference with the rates and snow we have coming 

[MJO812]

My forecast high tomorrow is 24.  I had highs in the teens for tomorrow earlier in the week.

This storm transformed so much . The cold air eased to make room for the primary to travel further west than earlier this week.

[ILoveWinter]

SWFEs aren't always great for the immediate metro as we typically do change over to sleet/zr at some point. However there have been several of them where it didn't matter due to the strong front end thump. Considering this is a stronger than normal SWFE, it's certainly possible we get insane rates early on.

[jm1220]

4 minutes ago, The 4 Seasons said:

2nd update and likely final call. We split up the initial range of 8-16" to 8-12" and 12-16". Think the city and LI fit well within 8-12", dont see them getting over a foot despite what the NWS thinks. Some reasons behind this conservative call:

• Though a lot of qpf falls as snow, many models bring significant warming H7-H8 during the height/back end of storm
• Ratios on BUFKIT look initially high for many areas but fall to around 10:1 or in some cases a bit lower, went a bit above 10:1 for average
• Excellent frontogensis will produce rates of 1-3" per hour for a while then move N/NE of the area
• Went with a blended approach mainly GFS/EC/Canadian and threw out warm outliers, NAM not used.
• 8-12" amounts most common with 12"+ well N/W of the city but think around 16 is the cap
• Dry air moves in and shuts off pcp any redeveloping snows will likely be N of MA boarder/dutchess/ulster after midnight/early monday

If any significant changes happen today well do an update before the storm as we still about 24hrs out. 

 

Thanks, I think that's very reasonable and what I'd go with. My guess for my backyard (NW Suffolk County) was 10" and Central Park around 9". I don't see the 12" NWS is predicting here unless we get the very high end to happen.

[Winterweatherlover]

5 minutes ago, jm1220 said:

Thanks, I think that's very reasonable and what I'd go with. My guess for my backyard (NW Suffolk County) was 10" and Central Park around 9". I don't see the 12" NWS is predicting here unless we get the very high end to happen.

Honestly if LI/NYC get 10 inches out of this at this point it would be a major win and a great storm. I am not even convinced the immediate NW suburbs are getting 10 inches at this point. I think the NWS is too bullish.

 

But if most of the area pulls off 9+ with an SWFE that's a huge win.

[nycsnow]

3 minutes ago, jm1220 said:

Thanks, I think that's very reasonable and what I'd go with. My guess for my backyard (NW Suffolk County) was 10" and Central Park around 9". I don't see the 12" NWS is predicting here unless we get the very high end to happen.

Or some of these meso short ranges to be right lol  

[WeatherGeek2025]

11 minutes ago, Jt17 said:

Can somebody post F27 from Fv3 vs. NAM. It's a wild difference.


.

[riverrat]

22 minutes ago, donsutherland1 said:

Adapted from Tayor Swift's "We Are Never Ever Getting Back Together."

We hadn’t synced a single run all month,
’Cause you said you needed space (What?)
Then you come around again and say,
“NAM, I miss you, swear the PNA’s gonna change, trust me.”
Remember how that lasted for a day?

You ditch me when the ridge* is gone,
Then beg me for that coastal bomb— “Show snow!” you plead.
But I’ve evolved, I’m done, I’ve got a mission: sabotage.

’Cause I am never, ever, ever, ever showing snow together.
Like, ever.
I’m gonna warm-nose every layer,
Torch the mid-levels ’til you suffer.
I’m never, ever, ever, ever showing snow together.
Like, ever.

Oh, you blamed me when the PNA stayed negative,
Ghosted me for globals, called me “clown guidance,” so repetitive.
So now I’m cranking 850s warm,
Killing totals storm by storm,
And every run you beg and pray—
I’ll melt it all away…

’Cause I am never, ever, ever, ever showing snow together.
Like, ever.

I’ll overdo the mixing,
I’ll break your wintry fever.
Yeah, we are never, ever, ever, ever getting snow together—
Like, ever.

*-PNA Ridge

Thanks for the humor!

[SACRUS]

 

12z RRFS (new / replace NAM)

 

Snow by 3/4AM

 

 

Snow through 2PM before mixing with sleet

 

 

 

 

[SACRUS]

 

[Stormlover74]

Nobody look at the rrfs. Its worse than the nam

[Winterweatherlover]

Just now, SACRUS said:

 

12z RRFS (new / replace NAM)

 

Snow by 3/4AM

 

 

Snow through 2PM before mixing with sleet

 

 

 

 

Yea sleet into central PA and no strong secondary is basically writing on the wall for anyone I80 or south. Again though the thump could save everyone.

[jm1220]

8 minutes ago, Winterweatherlover said:

Are there key locations in the south that we should be checking in terms of NAM predictions vs actual outcomes?

I'd look to maybe N KY, the colder models have places like just south of Louisville with significant snow but the NAM keeps it in OH/IN mainly. 

[nycsnow]

Just now, Winterweatherlover said:

Yea sleet into central PA and no strong secondary is basically writing on the wall for anyone I80 or south. Again though the thump could save everyone.

It’s a prototype for the Nam of course it’s gonna be like the NAM…. 0 other high res look like thet

[SACRUS]

 

[WeatherGeek2025]

i gotta revise my snowmap and my snow prediction, lowering by 40%

[nycsnow]

Another short term model not the nam

[Jt17]

 

Looks like it's papa NAM. All the other short range guidance says this look is 75 miles overdone not buying it.


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[SACRUS]

2 minutes ago, nycsnow said:

It’s a prototype for the Nam of course it’s gonna be like the NAM…. 0 other high res look like thet

RRFS (Next-Generation Replacement)

Core dynamics

FV3 (Finite-Volume Cubed-Sphere)

Same dynamical core as modern GFS

Part of NOAA’s Unified Forecast System (UFS)

Grid / algorithm

Unstructured cubed-sphere grid

Variable resolution

No lateral boundary conditions

Seamless global → regional scaling