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January 29-30, 2019 Arctic FROPA


WxUSAF

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33 minutes ago, psuhoffman said:

But the NAM jumps back and forth like this.  18z wet, 0z was dry, 6z wet, 12z dry.   How do you know which run is correct. Yea it’s tempting to go with the latest but I’ve seen the NAM drastically cut qpf right at game time and be wrong before too. Don’t get me wrong I’m not dismissing a fryer weaker solution, I’ve kinda expected that all along. But the NAM itself seems useless in determining which way it will go. 

The constant flips are probably why they aren't being weighted as heavily as the global's at this point. The whole long and shortwave pattern is probably difficult to discern for the NAM's at this point, but you have to lend some merit to it this close in. I would love to see what WPC and LWX are using for the basis of their forecast. Might be a blend of global handling of the H5 and H25 setup, coupled with the Super Ensemble plumes which are right where they have the forecast right now. 

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3 minutes ago, MillvilleWx said:

The constant flips are probably why they aren't being weighted as heavily as the global's at this point. The whole long and shortwave pattern is probably difficult to discern for the NAM's at this point, but you have to lend some merit to it this close in. I would love to see what WPC and LWX are using for the basis of their forecast. Might be a blend of global handling of the H5 and H25 setup, coupled with the Super Ensemble plumes which are right where they have the forecast right now. 

The NAM is a great idea as it has a much more accurate depiction of what the meso scale features of a storm actually look like.  BUT...its so jumpy with where it places those features that often it just adds more frustration and noise.  If they could somehow devise a model with the meso scale capabilities of the NAM but the consistency of the globals it would be a huge win.  Right now the euro is probably still best even at short range as it has pretty good resolution and doesn't flip flop all over usually imo.  Then you just have to use common sense in adjusting for meso scale features that it can't see.  

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this sort of reminds me of a system in the late 90s or 00ish that was a slow moving front with temps cold enough to snow.  the precip line was thin and it really didn't collapse east until the low transferred to the coast.  if this ends up similar we could bust high similar to that one.  if it ends up not getting organized in time, then that's where we end up with mangled, downsloping flakes.  at the very least, it's an interesting system.

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1 minute ago, psuhoffman said:

The NAM is a great idea as it has a much more accurate depiction of what the meso scale features of a storm actually look like.  BUT...its so jumpy with where it places those features that often it just adds more frustration and noise.  If they could somehow devise a model with the meso scale capabilities of the NAM but the consistency of the globals it would be a huge win.  Right now the euro is probably still best even at short range as it has pretty good resolution and doesn't flip flop all over usually imo.  Then you just have to use common sense in adjusting for meso scale features that it can't see.  

The biggest issue with the NAM's is the model is prone to massive swings with just subtle changes in the upper levels. Idk if it's a spatial resolution issue or just the physics in the model are not capable of minor adjustments at the surface given the shifts aloft. The ground truth will probably lie somewhere between the current meso depiction and the global's. The jet streak strength and positioning over PA is really important for today. A more pronounced jet will likely generate a better qpf field and overall dendritic process. 

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8 minutes ago, MillvilleWx said:

The squall depiction on the NAM Nest still looks pretty prolific for north of I-70. Could be a fun day tomorrow for some. Potential low vis and brief heavy snow with big, fluffy dendrites. 

Pretty impressive all the way to the coast on the 3km. Even manages to scrape my yard along the way.

nam3km_ref_frzn_neus_34.thumb.png.f2981a2cc78d648227dd200e4301277b.png

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Just now, losetoa6 said:

Yea man...and it seems some really gusty winds mix down if your yard is lucky enough to be under the squall line . 3k advertising 50 mph 

Steep low level lapse rates with mixing to just under 700mb  would bring upper 30's to 40's under any of those squalls. Potential brief whiteout possible with these as they blow through. Very high ratio snow too. 15-20:1 without question. 

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13 minutes ago, MillvilleWx said:

The squall depiction on the NAM Nest still looks pretty prolific for north of I-70. Could be a fun day tomorrow for some. Potential low vis and brief heavy snow with big, fluffy dendrites. 

Yup. However, it did look better in yesterday's runs up through 6z this morning. Kind of a step back at 12z. 

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3 minutes ago, MillvilleWx said:

Steep low level lapse rates with mixing to just under 700mb  would bring upper 30's to 40's under any of those squalls. Potential brief whiteout possible with these as they blow through. Very high ratio snow too. 15-20:1 without question. 

            followed by a rapid and dramatic temperature drop.    would be crazy if the bigger commute issues end up occurring Wednesday afternoon instead of today.

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1 minute ago, MD Snow said:

Yup. However, it did look better in yesterday's runs up through 6z this morning. Kind of a step back at 12z. 

Squalls are tough to gauge leading up to the event. It'll bounce around overtime and models mishandle them so often. It'll be a game time type of deal since it's convective based. 

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Just now, high risk said:

            followed by a rapid and dramatic temperature drop.    would be crazy if the bigger commute issues end up occurring Wednesday afternoon instead of today.

It very well could be. Squalls are a mess to contend with. I dealt with a few while I was at school in PA. Bring vis down below a 1/4 mile in a snap of the fingers. 

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Just now, high risk said:

            followed by a rapid and dramatic temperature drop.    would be crazy if the bigger commute issues end up occurring Wednesday afternoon instead of today.

Reminds me of the sneaky Wednesday evening event in 2016 that iced things up before the weekend snowstorm.  Everyone was focused on the impending big snow and the roads were an ice rink from a coating of snow.

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