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FORECAST DISCUSSION: "The Storm They Couldn't Punt" 2/7-2/9


HM

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Question for the mods... correct me if I am wrong, but aren't we at the point where we favor short range models over the GFS?  Not being a weenie for the NAM... but is there any weight one way or the other?  Mesoscale models maybe for deformation banding and CCB?

I'd weight the SREFs a lot higher than the op NAM, imo

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Absolutely.  Thank you for answering.  Assuming the Euro is in similar "already served its usefulness" range similar to GFS?

Euro is a bit better, only because of the finer resolution and better convective parameterization schemes. It's basically almost a mesoscale model already.

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It goes without saying that there is going to be a sharp cut-off between those with plowable snow on Saturday and those with essentially nothing.  Right now, it is anybody's guess where that cutoff will be, but I guarantee that at least a few of us will be miserable and (hopefully) at least a couple of us (and ideally most of us) are going to be very happy.  Sadly, only time is going to tell on this one.    

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The GFS is pretty cool between 21z-00z as the northern stream influence affects omega. The southern stream's initial forcing gets as far west as NYC / adjacent NE NJ suburbs. But, as the UVM expands and intensifies in response to the incoming deformation zone, an awesome "comma head" blossoms up over the area. Despite the weird 00z 0°C at 850mb, wet bulbs are below / near from PHL north with the lower RH there (around 90%). Looks like good dendrite making on the soundings but not quite as unstable as the NAM of course. Looking forward to the euro.

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Question for the mods... correct me if I am wrong, but aren't we at the point where we favor short range models over the GFS?  Not being a weenie for the NAM... but is there any weight one way or the other?  Mesoscale models maybe for deformation banding and CCB?

 

Even though precip will be starting in less than 24 hours, the "big show" (or in this case, the big snow) for anybody in the wider Philly area won't be developing until later tomorrow and more likely overnight for those in the I-95 corridor and to the east, so the good stuff is really 36+ hours out and well beyond the NAM's wheelhouse (if it even has a wheelhouse).  

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Just ran the Wxsim model with the NAM 12z and GFS 6z - still think this is running a bit too warm but here is the breakdown for the NW Philly burbs

Mix of Snow/Rain beginning by 5am tomorrow morning - the mix continues all day with temps just above freezing (I have my doubts on this aspect) around 0.59" of precip falls before turning quickly to heavy snow tomorrow evening by 6pm - snow continues then till almost daybreak saturday AM with between 4" to 6" of snow before ending

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If you live west of the Pocono plateau, down the app trail, through carbon county, the I-81 corridor, Tamaqua, Pottsville down to Allentown to reading on west I would be worried about subsidence and that sharp cut off. Traditionally that seems to be where it sets up. Probably too soon to say, but once those radar echoes halt the northwest progression, it's game over if you're outside of that area once the storm is due east and pulling away.

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If you live west of the Pocono plateau, down the app trail, through carbon county, the I-81 corridor, Tamaqua, Pottsville down to Allentown to reading on west I would be worried about subsidence and that sharp cut off. Traditionally that seems to be where it sets up. Probably too soon to say, but once those radar echoes halt the northwest progression, it's game over if you're outside of that area once the storm is due east and pulling away.

 

100% agree

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If you live west of the Pocono plateau, down the app trail, through carbon county, the I-81 corridor, Tamaqua, Pottsville down to Allentown to reading on west I would be worried about subsidence and that sharp cut off. Traditionally that seems to be where it sets up. Probably too soon to say, but once those radar echoes halt the northwest progression, it's game over if you're outside of that area once the storm is due east and pulling away.

 

Absolutely, and it has been a concern of mine. We've seen it plenty of times during the back to back epic winters a few years back. Many of those storms had tight gradients for one reason or another, and we ended up with 2 or 3 inches in my location, while areas farther south, east, and northeast by no more than 100 miles got pounded.

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Between 00z-06z on the GFS, the soundings grow pretty impressive across eastern PA into PHL and northern/central NJ. There is a pretty large SGZ for our area with strong frontogensis/mid level convergence. Definitely the increasingly cold profiles / convergence (less wind) means that I was wrong about ratios before. While they may be on the order of 5-10:1 before 00z, they would increase above 10:1 with this back edge late evening / overnight. I'll let the Mt. Holly mets take it from here but it looks like a solid chance at 12-18:1 ratios with this part of the storm.

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Between 00z-06z on the GFS, the soundings grow pretty impressive across eastern PA into PHL and northern/central NJ. There is a pretty large SGZ for our area with strong frontogensis/mid level convergence. Definitely the increasingly cold profiles / convergence (less wind) means that I was wrong about ratios before. While they may be on the order of 5-10:1 before 00z, they would increase above 10:1 with this back edge late evening / overnight. I'll let the Mt. Holly mets take it from here but it looks like a solid chance at 12-18:1 ratios with this part of the storm.

Is it all of eastern pa?

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Between 00z-06z on the GFS, the soundings grow pretty impressive across eastern PA into PHL and northern/central NJ. There is a pretty large SGZ for our area with strong frontogensis/mid level convergence. Definitely the increasingly cold profiles / convergence (less wind) means that I was wrong about ratios before. While they may be on the order of 5-10:1 before 00z, they would increase above 10:1 with this back edge late evening / overnight. I'll let the Mt. Holly mets take it from here but it looks like a solid chance at 12-18:1 ratios with this part of the storm.

15:1 for a time after 00z is possible. Would not go much higher than that. 

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