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January 19-20th Winter Storm Threat


Rjay

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why are the gfs models even being looked at?  The NAM is deadly at this range and combined with the Euro pretty much tells the story. The GFS is way too warm and MT Holly has indicated that by extending their winter storm watches further SE. The biggest issue is the transition period and how long and that will not be determined until Sat  morning runs

 

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The NSSL convection-allowing models and some other hi-res guidance show the potential for icing throughout most of the city even if the warm front makes it to central NJ. This is not necessarily in their wheelhouse yet, but I think it's a good illustration of how low-level cold hangs tough directly north of the surface front. This is the warmest panel on the 12Z NSSL WRF, which gets the freezing line to JFK for an hour and then rapidly brings temps down into the 20s by 12Z Sunday. NSSL.thumb.png.2d7e0c45ee470b1ce93b6a1003b167bf.png

Given that the heaviest precip will be around during this period, it will be important to see if the globals correct S/E in the next 24 hours or if the CAMs trend north. 

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11 minutes ago, purduewx80 said:

The NSSL convection-allowing models and some other hi-res guidance show the potential for icing throughout most of the city even if the warm front makes it to central NJ. This is not necessarily in their wheelhouse yet, but I think it's a good illustration of how low-level cold hangs tough directly north of the surface front. This is the warmest panel on the 12Z NSSL WRF, which gets the freezing line to JFK for an hour and then rapidly brings temps down into the 20s by 12Z Sunday. NSSL.thumb.png.2d7e0c45ee470b1ce93b6a1003b167bf.png

Given that the heaviest precip will be around during this period, it will be important to see if the globals correct S/E in the next 24 hours or if the CAMs trend north. 

This model seems much colder than any other by a lot in terms of surface temps.. Is it accurate?

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4 minutes ago, mikem81 said:

Its 5 degrees too cold for current OBS in the NYC area. I am sitting at 39 here in Nassau. Has me at 34

fair point. if you apply that bias and assume it holds for the event, northern and western parts of the metro still would see predominantly pellets and then freezing rain (after the evening snow) before precip ends. again it's important to watch trends w/ that air mass once it comes into the NE tonight/tomorrow. even today no one model has this pegged.

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5 minutes ago, mikem81 said:

Its 5 degrees too cold for current OBS in the NYC area. I am sitting at 39 here in Nassau. Has me at 34

Down here in SE PA it's the only model that has nailed the temps. Everyone else had us in the low 40's, we're currently at 33. PHL currently at 35. Doubt we get our projected highs with the heavy cloud cover in place and this is the only model that has absolutely nailed it. 

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27 minutes ago, purduewx80 said:

The NSSL convection-allowing models and some other hi-res guidance show the potential for icing throughout most of the city even if the warm front makes it to central NJ. This is not necessarily in their wheelhouse yet, but I think it's a good illustration of how low-level cold hangs tough directly north of the surface front. This is the warmest panel on the 12Z NSSL WRF, which gets the freezing line to JFK for an hour and then rapidly brings temps down into the 20s by 12Z Sunday. NSSL.thumb.png.2d7e0c45ee470b1ce93b6a1003b167bf.png

Given that the heaviest precip will be around during this period, it will be important to see if the globals correct S/E in the next 24 hours or if the CAMs trend north. 

Awesome point, thanks!  Question for you: obviously, meteorologists, especially those in the local NWS offices, know a lot more about meteorology (and sometimes their areas) than the vast majority of non-pros who post here and elsewhere and that we should assume that they're not just basing their forecasts on model output or even consensus model output.  Do I have that right?  I assume that what you just posted and presumably many other diagnostic and data analysis tools either aren't available or are rarely used by most posters on weather boards and that it's safe to assume the NWS and other pros have a lot more at their disposal when making a forecasts.  #hopingtheNWSiscorrect...

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Just now, RU848789 said:

Awesome point, thanks!  Question for you: obviously, meteorologists, especially those in the local NWS offices, know a lot more about meteorology (and sometimes their areas) than the vast majority of non-pros who post here and elsewhere and that we should assume that they're not just basing their forecasts on model output or even consensus model output.  Do I have that right?  I assume that what you just posted and presumably many other diagnostic and data analysis tools either aren't available or are rarely used by most posters on weather boards and that it's safe to assume the NWS and other pros have a lot more at their disposal when making a forecasts.  #hopingtheNWSiscorrect...

Yes, there are a number of tools and in-house models available to both private sector and NWS mets that the public doesn't have access to. Local knowledge is important, but understanding model biases is just as important. Probabilistic guidance is becoming an increasingly used tool to support decision making.

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Interestingly, 3KM NAM shows winds in NYC and LI stay NE for the duration of the event, so temps stay 32-34.  We'll see what happens but it wouldn't take much to turn this into a nasty ice storm with a NAM track.  Slightly lower wetbulb in the source airmass and everyone NYC north is in business for ice.

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1 hour ago, bluewave said:

Given WPC declaration of the 12Z NAM being an outlier (now confirmed with the Euro remaining warm/wet), I'd be surprised if the NWS doesn't drop the winter storm watches from the southernmost counties under them right now, like Upper Montco/Bucks and Hunterdon/Somerset from the NWS-Mt. Holly and Union/Essex (maybe)/Hudson/NYC/LI from the NWS-NYC.  I could see those locations getting winter weather advisories, since some snow/sleet is still being modeled (a few inches not up to 6"). The next tier N and W might stay watches or could be converted to warnings if they have high confidence in getting to 6" for most of their areas. Or maybe they have different assumptions and they won't budge (or at least not yet), since it's not only about models (they do have access to advanced data analysis and diagnostics tools that the public does not).   Just my opinion...

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Starting tonight, I will be watching how real time observations upstream may match or not match model data projections to better predict accuracy. Actually, that has already begun to be discussed I believe.  Regardless of what the models say now, it is soon game time and we watch play by play. Time soon for the mesos to chime in. 

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