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Clipper Threat 1/22/13-1/23/13


Allsnow

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I believe snow ratios are tied to two issues. Cold temps resulting in dry powdery snow, the fluff factor, and also conditions in the snow growth region of the atmosphere which determines the type of flakes that form. Cold temps aloft are just one part of that equation. The type (shape and structure) of flakes determine how they accumulate. Certain shapes create greater air spaces thus less total volume of snow accumulates to a greater depth. It is possible to have a dry powdery snow with snow flake structure not conducive to very high ratios. Being cold ratios will be higher and probably in the 12-16 to 1 range but much higher than that will require some serious optimal snow growth conditions. I am sure some one who knows the technical issues can explain this further and better.

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there will be no 40:1 ratios anywhere on this forum.

In NW NJ I have had 40:1 ratios many times with these types of clipper situations depicted on the 84 hr NAM. Areas to the East for NYC and so on would likely be in the 20:1 range. Again, I am speaking of the Wednesday night storm depicted on the 84hr NAM. Right now the model shows surface temps of around 18 degrees here at 7pm on Wednesday with the 850 level at -20. Snow is on our doorsteps at that point.

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I believe snow ratios are tied to two issues. Cold temps resulting in dry powdery snow, the fluff factor, and also conditions in the snow growth region of the atmosphere which determines the type of flakes that form. Cold temps aloft are just one part of that equation. The type (shape and structure) of flakes determine how they accumulate. Certain shapes create greater air spaces thus less total volume of snow accumulates to a greater depth. It is possible to have a dry powdery snow with snow flake structure not conducive to very high ratios. Being cold ratios will be higher and probably in the 12-16 to 1 range but much higher than that will require some serious optimal snow growth conditions. I am sure some one who knows the technical issues can explain this further and better.

This is correct. I'm mobile now so I don't have the time to elaborate too much but this is definitely true. You also need good omega (lift) in the snow growth region, and you want your snow growth region saturated with temperatures between -12 C and -18 C.

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The European is prob goin to look just dry , You just gotta  look at the finer high res models for QPF  from here on in .

The globals look at at bigger picture , the high res  are coarser and sometimes pick up mesoscale features better .

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Great discussion from a Met in the New England forum I am posting below about why the globals won't get this one right.

the globals aren't going to come around in the sense they aren't going to accurately represent the NORLUN trough feature by low-level convergence or qpf.

In terms of general snowfall across SNE, they're going to be alright...but not the NORLUN feature itself.

I mean the GFS might have 1/4" of QPF in a LES area that gets 2 ft of snow lol. A 30km spectral model doesn't have the resolution or non-hydrostatic dynamic to resolve something like that.

You'd like to see the Euro bump up stuff to a degree though, since it has 12km resolution it can at least attempt to resolve more mesoscale features.

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Great discussion from a Met in the New England forum I am posting below about why the globals won't get this one right.

the globals aren't going to come around in the sense they aren't going to accurately represent the NORLUN trough feature by low-level convergence or qpf.

In terms of general snowfall across SNE, they're going to be alright...but not the NORLUN feature itself.

I mean the GFS might have 1/4" of QPF in a LES area that gets 2 ft of snow lol. A 30km spectral model doesn't have the resolution or non-hydrostatic dynamic to resolve something like that.

You'd like to see the Euro bump up stuff to a degree though, since it has 12km resolution it can at least attempt to resolve more mesoscale features.

 

I only agree with him because he agrees with me .  JK . Its true the Euro is coarser then the GFS , so thats a fair point .

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Here is another met in the New England forum:

Even though the Euro has a higher resolution than the GFS it's still a global model. It has different convective parametrization schemes than a mesoscale model and is also hydrostatic.... so while the higher resolution helps for an intrinsically mesoscale (and convective, you could say) phenomenon it may not be of much use.

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The NAM is a garbage model, not sure why people still use it. GFS/EURO/GGEM are all dry for the area, coating at best.

The NAM is NOT a garbage model. It picked up the trends of many many storms before other models have even had a hint, even at its longer range. It is a high resolution model and one of the only ones that picks out small details such as where specific bands will set up. For Monday night and Tuesday, it shows a band of snow moving through PHL and then NYC....a bust for a couple hours that gives around an inch or so. The other models don't show this. It is either because it is not going to happen or the others are not picking up any specifics of what will happen. We'll see....but I am pretty sure it will be the first :)

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Usually the EURO would be king but with its failure on the last event, the fact that it stands virtually alone, and the fact that the NAM/SREFS have not backed down makes me think they might be on to something. Usually they jump off their crazy trains after a run or two. But who knows, maybe they all are out to lunch :)

-skisheep

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Think of it this way...have you ever seen a quick inch or two from snow showers that wasn't part of a big storm or large organized area of precip? I'm sure we all have....now think....was this modeled to give me an inch or two of snow ? Nope....those situations usually just show up as light green (0.1 or less) of qpf on most models

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Yes, everyone is still .10+ for the most part, but the .25+ area shifted east again. This is clearly a big hit only for eastern Long Island and eastern New England, but the rest of us should get a dusting to one or two inches.

 

shouldn't someone still get 4 inches with those 40:1 ratios?

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