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February 11 -12 Winter Storm Threat


NEG NAO

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6 hours ago, RU848789 said:

At the risk of being accused of beating and stomping on the neck of a dead horse, this is why I hate those "snow only" maps in a mixed precip events and prefer the TT style sleet+snow (all at 10:1, so I know the LE falling in frozen form) maps.  On the 12Z CMC, the storm doesn't look like much of a big deal for the 95 corridor, including NYC, but that's wrong.  Let's use the 12Z CMC and NYC just to illustrate (same holds true down to at least New Brunswick) what I'm talking about by analyzing what the model says at a deeper level (not a forecast).  

  • The sounding for NYC is clearly for snow at 7 am, with the whole column well below 32F down to the surface at 26F
  • The sounding for NYC is then just barely sleet at 1 pm with 700-850 mbar, just barely going above 32F, but with all of 850 mbar to the surface being well below 32F and the surface at 29F. 
  • The sounding for NYC at 7 pm is still for sleet, with 700-900 mbar above 32F, but with the column below that well below 32F until just at the surface, where it's 33F - sleet will certainly form falling through ~3000 feet of sub-32F column and shouldn't melt from the last 100 feet or so being above 32F to the surface at 33F, IMO.    
  • But the snow only map shows only 1/2" of snow falling in NYC (and Edison/NB) from 7 am to 7 pm, implying a change to sleet soon after 7 am (which is questionable, but irrelevant to my point).  But the model then is completely ignoring close to 12 hours of sleet and the precip map shows 0.5" LE falling in NYC between 7 am and 7 pm (and 0.7" in NB), plus it's likely that that sleet signature for NYC lasts another couple of hours to get NYC to maybe 0.7" LE as sleet, like NB. 
  • A storm with 1-2" of snow on the map, like the 12Z CMC, looks benign.  A storm with 1-2" of snow, followed by 0.7" of LE as sleet, which is about 2" of sleet (at a 3:1 ratio) is a far different and much more impactful storm, as that's a total of 0.8-0.9" LE in frozen form (8-9" worth of snow, even if it will only be 3-4" on the ground) and that mass is what's critical for shoveling, plowing, driving, etc.  Not as pretty as snow and much less of a visibility issue, but very impactful. 
  • Because of this, I think the NWS might issue watches, which are usually reserved for 6" of pure snow, for the 95 corridor and NW of there, since the frozen equivalent will likely be 6" of "snow equivalent" or more. The risk of 0.1" or more of freezing rain might also tip the scales towards watches (and warnings tomorrow morning if the models don't change much). We'll see soon.
  • One more thing.  If we get 0.6-1.0" of LE in frozen form for the Trenton-NYC corridor, as almost every model is showing, that amount of frozen precip will likely absorb much of the subsequent 0.5-1.0" of rain that likely falls after the changeover to all rain (especially if it's on the 0.5" side of things as rain), creating a slushy mess holding about 1.5-2.0" of LE - a bit of melting will obviously occur with temps in the mid/upper 30s and rain, but I'd guess <25% melting.  However, if the CMC is right and we hit 50F on Wednesday, lots of melting will occur (other models top out at 35-40F, so big variance there in melting rate/amount).  



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Using model soundings to infer p-type?  Sacrilege!

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8 hours ago, SnowGoose69 said:

The setup was nowhere near as good.  High wasn’t a one piece anchored high.  It was a sprawled our high with the neck positioned too far west across Quebec so you just didn’t get the proper CAD signature.  Also the air mass wasn’t as good in place ahead of the storm

Exactly I'm a realist and usually less toward cautiously pessimitic but even I can see this setup is different

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6 minutes ago, Brasiluvsnow said:

and the rumor is that the NAM does well with CAD ,,,,,,,OH MY TIME WILL TELL

 

if it is sleet this is going to be no big deal on the roads in the immediate NYC Metro because temps are going to be in the lower 30's and they will be putting tons of salt down and most of it will fall during daylight with more traffic

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1 minute ago, NEG NAO said:

if it is sleet this is going to be no big deal on the roads in the immediate NYC Metro because temps are going to be in the lower 30's and they will be putting tons of salt down and most of it will all during daylight with more traffic

Maybe in Manhattan but the sleet will accumulate all over the outer boroughs as long as it's at or below freezing, even if it's slightly above freezing it may accumulate if theres already sleet/snow on the ground. 

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3 minutes ago, David-LI said:

NAM would be a Winter Storm Watch scenario for the metro area

Upton was too conservative in November and too bullish for MLK, now they seem back to being conservative, I would expect the WSW to be extended to at least Putnam, Rockland Western Bergen, and Northern Westchester with WWA for the rest of the tri state area.

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3 minutes ago, NEG NAO said:

if it is sleet this is going to be no big deal on the roads in the immediate NYC Metro because temps are going to be in the lower 30's and they will be putting tons of salt down and most of it will fall during daylight with more traffic

I wouldn't chance it. But that's me.

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Just now, weatherpruf said:

I wouldn't chance it. But that's me.

our side roads in Colonia may be icy but New Dover Rd and inman ave will have a ton of salt and tomorrow those stupid loud trucks will be running around here all day spreading that chemical on the roads

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3 minutes ago, weatherpruf said:

March 2017

Yea these storms tend to happen more in Feburary and March than earlier in the winter, I guess due to the ocean being colder? Even last year I remember there was a storm I think in Mid Feburary where there was a decent amount of ZR in parts of the city before the change to rain. 

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