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January 19-20th Winter Storm Threat


Rjay

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2 minutes ago, SnoSki14 said:

Surface temps on the Gfs have actually cooled off substantially over the past 2-3 runs. Went from mid to upper 40s to mid 30s. 

You figured it would catch onto that sooner or later.  Reality is I don’t think anyone outside of south shore of Nassau and Suffolk county will really get over 34-38 during this event 

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Everyone should understand there are still going to be changes in the modeling up through the event due primarily to three things:

  • While some of the Pacific energy was sampled on the West Coast this morning, the backside jet (500-250mb) will be better sampled on the 00z soundings. I've seen this matter countless times for storms in the Midwest, specifically with the GFS and NAM, no matter how good the ingestion of satellite data is these days.
  • The subtleties of its phasing with an arm of the polar vortex - timing and location of this still isn't ironed out, as many have pointed out.
  • Convection will play havoc with surface low and low-level jet development. This system will be highly convective through the mid-south due to warmth and moisture from the Gulf meeting up with the Arctic air mass, in addition to all the jet dynamics. More often than not, convection may "drag" surface features (including the sfc low) towards the higher instability/waa until jet dynamics and vorticity advection take over (which is what causes the low to bomb out well NE of here). Even the hi-res models miss this all the time. 

There is at least some model evidence now to support the idea that even if the surface low(s) pass just south of the region, surface temps could stay sub-freezing throughout the city and most of LI as ageostrophic flow out of the high to our north outperforms. It's not just the RPM showing this. I see no reason to doubt a front-end thump here followed by a brief transition to sleet before primarily liquid precip falls. I wouldn't count out some back side pellets or snow either, although for now that looks light. 

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According to the NWS AFD the other day, tonight's 0Z is the first suite where we'll have the southern stream low fully ashore and well-sampled, meaning we should have more accurate, fuller initial conditions to feed into the models, so if there's a time when we might see a modest to significant shift (in either direction) 0Z would be it.  One can hope.  

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1 minute ago, purduewx80 said:

Everyone should understand there are still going to be changes in the modeling up through the event due primarily to three things:

  • While some of the Pacific energy was sampled on the West Coast this morning, the backside jet (500-250mb) will be better sampled on the 00z soundings. I've seen this matter countless times for storms in the Midwest, specifically with the GFS and NAM, no matter how good the ingestion of satellite data is these days.
  • The subtleties of its phasing with an arm of the polar vortex - timing and location of this still isn't ironed out, as many have pointed out.
  • Convection will play havoc with surface low and low-level jet development. This system will be highly convective through the mid-south due to warmth and moisture from the Gulf meeting up with the Arctic air mass, in addition to all the jet dynamics. More often than not, convection may "drag" surface features (including the sfc low) towards the higher instability/waa until jet dynamics and vorticity advection take over (which is what causes the low to bomb out well NE of here). Even the hi-res models miss this all the time. 

There is at least some model evidence now to support the idea that even if the surface low(s) pass just south of the region, surface temps could stay sub-freezing throughout the city and most of LI as ageostrophic flow out of the high to our north outperforms. It's not just the RPM showing this. I see no reason to doubt a front-end thump here followed by a brief transition to sleet before primarily liquid precip falls. I wouldn't count out some back side pellets or snow either, although for now that looks light. 

First bullet looks like what I just wrote.  Just better said, lol.  Great post.  

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24 minutes ago, SnowGoose69 said:

You figured it would catch onto that sooner or later.  Reality is I don’t think anyone outside of south shore of Nassau and Suffolk county will really get over 34-38 during this event 

Agree not that it matters much although might mitigate washing it all away if there was a front end dump 

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1 hour ago, SnowGoose69 said:

Yeah NWS amounts for city and Long Island are too high at the moment.  I wouldn’t want to go any higher than 1-2 right now at all.  I would probably hedge it as 1-3 so if I did have to up things later the change wouldn’t be as significant to the eyes or mind of the public 

Pretty sure this is based off what happened in November, this time they want to go reverse and hype it up, better to be safe on their end and overestimate totals rather than underestimate    

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3 minutes ago, weatherpruf said:

That's about the most explanation you'll get from him. He's strictly for those in the know. But a decent fellow it seems.

I think he's implying that the mountains are gonna carve up (dry out) some moisture with that track. Since it goes right through the apps. 

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25 minutes ago, allgame830 said:

Do explain what you mean or someone in here?? Thanks in advance 

 

12 minutes ago, weatherpruf said:

That's about the most explanation you'll get from him. He's strictly for those in the know. But a decent fellow it seems.

What's not clear about the post???

I believe a drier system, than is cast ATM  will come thru the metro

NAM  guidance shows a decrease in QPF by almost a half inch at 18z

:arrowhead:  that's a clipper track..... if you ask me

 

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14 minutes ago, Doorman said:

 

What's not clear about the post???

I believe a drier system, than is cast ATM  will come thru the metro

NAM  guidance shows a decrease in QPF by almost a half inch at 18z

:arrowhead:  that's a clipper track..... if you ask me

 

I surmised as much, but not everyone here would. But it's ok. Not to worry. You're a man of few words. Nothing wrong with it. You have something to say, while I just like to say something...

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16 minutes ago, Doorman said:

 

What's not clear about the post???

I believe a drier system, than is cast ATM  will come thru the metro

NAM  guidance shows a decrease in QPF by almost a half inch at 18z

:arrowhead:  that's a clipper track..... if you ask me

 

By the way, kinda hope you're right, who needs a lot of ice and ZR. Not me. Not anyone.

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25 minutes ago, Doorman said:

 

What's not clear about the post???

I believe a drier system, than is cast ATM  will come thru the metro

NAM  guidance shows a decrease in QPF by almost a half inch at 18z

:arrowhead:  that's a clipper track..... if you ask me

 

The euro at 12z also chopped back on QPF from 2.5 to even 3 inches in spots to a more general 1.5-2

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8 minutes ago, tim said:

...my estimated observation @7am sunday morning...37* with heavy rain with <1" of snow OTG..

not expecting much out here.:weep:

Same for me. I'll be in Long Beach this weekend where it'll probably be a quick inch or two over to rain. Where I am now may be up to a few inches and some sleet before going to rain, but this isn't the type of storm that does well on the coastal plain. It's your classic North and West storm. 

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