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Discussion-OBS snow event sometime between 06z Thu 2/20-12z Fri 2/21?


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10 minutes ago, SnoSki14 said:

Congrats Virginia. If this happens I happily welcome Spring 

Seriously, if SE VA and Delmarva end with significantly more snow than NYC and get crushed yet again when we get cirrus or another BS 1-3” fringe, spring needs to get here asap. 

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48 minutes ago, MANDA said:

That storm was not locked in until the afternoon of.  The LFM lost it on the night before.  I remember it very well.  The morning of nobody was predicting 12" for NYC, never mind 20".  I THINK maybe forecasts the morning of were in the 3-6" range.

we got let out of school at noon that day

February 1983 was a lot like PD2 and January 2016

All in strong el ninos, all trended north.

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Why are we talking about storms that disappeared and then came back. Obviously we know that can happen. Every storm is unique. Just as we can see things turn more positive in upcoming runs, it’s equally likely that things stay the same or trend worse. No amount of talking about past storms changed that. 

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I missed the last 24 hours of models. Can someone please give me a brief rundown of where we stand? Seems like 0Z runs were great and then today everything fell apart except for the GEFS trending better as everything else trended worse?

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Just now, EastonSN+ said:

If it does end up as depicted by the Euro congrats Delmarva. 

I have to think that this may be their snowiest year in history if this comes through. 

Look up 1965-66, Norfolk Virginia, 40 plus inches of snow while we had 20 something (a normal winter for us,  a historic one for them.) Our epic winter came the following year, 1966-67, after a historically hot and dry summer, 4 days of 100+ with 107 at LGA, 104 at JFK and 103 at NYC.

The real head scratcher is this is a la nina, when such things are not supposed to happen.

 

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1 minute ago, allgame830 said:

That’s a pretty dramatic lean west if you ask me. 

It seems that there's two camps, one which is stronger and is closer to the coast and the other camp wish gains a certain amount of latitude then heads almost due east which is what the app did. 

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4 minutes ago, EastonSN+ said:

It seems that there's two camps, one which is stronger and is closer to the coast and the other camp wish gains a certain amount of latitude then heads almost due east which is what the app did. 

Get that trend out west to reverse and it's game on.  If it doesn't this will slip south and east and we'll end up near the fringe. 

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On 2/14/2025 at 3:57 PM, brooklynwx99 said:

Next week's system has become increasingly ominous and holds potential for significant to major impacts from DC - NYC and even BOS. There are a few features that make this such a favorable setup, mirroring past major and even historic storms:

Untitled.png.26111f868f6c57054c3facce7edb5f42.png

  1. The most important feature of this setup is the retrograding and decaying west-based -NAO that migrates into central Canada. This is perhaps the most important feature for major EC snowstorms, and it is a huge factor here, as it slows the pattern down and locks in confluence. It also leads to the "banana" HP that often develops in these setups due to NVA downstream of the block.
  2. This is a lobe of the polar vortex (PV) that is the impetus for the storm threat. This lobe becomes trapped under the block and will be forced to pivot under it, leading to a potential phase with the southern stream vort (x) over TX/OK. This kind of slow-moving, amplified ULL is also a main feature of major storm threats.
  3. As is common in these setups, a disturbance, either coastal or otherwise, amplifies into the northern Atlantic and becomes trapped by the block, leading to a 50/50 ULL that departs. This is crucial for establishing confluence, which keeps heights in check downstream of the amplifying trough. Note how heights are zonal over ME and Atlantic Canada.
  4. Last but not least, there is a transient spike in heights over the Pacific NW that links up with the blocking. This is a crucial piece of the puzzle... if that disturbance offshore destructively interferes with the blossoming +PNA, you get a weaker solution. However, the trend has been for constructive interference, which helps lead to downstream amplification.

1376216728_Screenshot2025-02-14145159.png.dad7222a089003b6b64bc4a04f687a62.png

It's also worth noting that this setup very closely mirrors past setups that delivered historic snowfall to the northern Mid-Atlantic. Notice the 500mb composite that has all four main features... the retrograding and decaying block, the amplifying trough over the MS River Valley, departing confluence, and a brief PNA spike as the storm is getting its act together.

Suffice it to say, this is probably the best synoptic setup that we have seen enter the medium range since February 2021 and it does hold the potential to be just as impactful. The GFS not being on board is pretty common in these setups. However, we will want to see this amplification signal enter the 96 hour window, so if we see this signal last into Monday, talks about a legitimate major snowstorm will hold more weight. Right now, it's worth being cautious, but the pattern has been screaming this kind of outcome for a week now, and it is bolstered by past outcomes.

Somehow I missed this yesterday - fantastic post, thanks!  And thanks for posting it here, also.  Loved your inclusion of the historical anomalies associated with NYC snowfalls over 18" over 30 years and your excellent discussion of how the current projected pattern matches these features, as well as the easy-to-understand graphics showing what you discussed. I'm guessing that's how you guys see the 500 mbar pattern 24 to maybe 48 hours before the event in a model run and say "we're loaded for a big snowstorm" (or not if you don't see it) - would that be correct?  I've never studied synoptics, so don't have much feel for how the pros infer this.  

I do have a couple of questions, though, if you can indulge me: i) I see that you showed the Euro pattern about a day prior to our potential event start on Thursday to match the NCEP graphic which says the anomaly is seen 1 day in advance ("preloading"), but I was wondering if one sees this anomalous pattern for a few days before such an event and not just at 1 day before the event (and could that give one more lead time on confidence in a big snowstorm); and ii) I get that this is the composite anomaly for 18" snowstorms, but is there data on how often such anomalies occur and what percentage of them lead to 18" snowstorms for NYC (or even any snow)?  I would imagine there's some percentage of time when these patterns don't lead to big snow, although maybe less frequently when they're as close to the event as 1 day before the event, but that's just a gut instinct.  TIA.

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2 hours ago, mob1 said:

There was a storm earlier this year that had an almost identical progression to this (I'm almost sure it's @Stormlover74's avatar).

 

Models showed an absolute bomb for a few cycles despite a tainted ridge, and eventually it showed the ridge rolling over and the storm stayed wayyyyyy out to sea. 

That one was mostly a gfs storm. The other models never really got on board then the gfs lost it

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1 hour ago, Rjay said:

Get that trend out west to reverse and it's game on.  If it doesn't this will slip south and east and we'll end up near the fringe. 

FWIW, 18z was a start. this is a nice change with less destructive interference out west and a more amped ULL

IMG_1800.thumb.gif.38b4e8fb8d80037bda09ac69e457466b.gif

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Some people jumping ship way too early, it's kind of silly actually. Again, most models were showing a huge storm just last night so it's way too early to give up after one model suite (I hardly count the 18z models which tend to have wonky solutions). IF the trend continues tonight then more concern should be had but even then it'll still be too early to make any sweeping statements about what will happen.

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