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February 2016 Forecasts/Disco/Obs


snowman19

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You should stop assuming. Wet snow doesn't mean non accumulating snow. It means that you're not going to get 6" of snow out of a half inch liquid.

 

This is where you lose me and many others 

 

As modeled that`s 4 to 5 out of .5  What are you talking about 

 

You are missing what the model run showed you . 

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Let's see what the soundings show when they come out.

 

 

Only what it is showing 

6 days out . Only as per model/ not a forecast. 

 

KNYC

Hour 156 

33/28 

850 -2

925 - 3

.2

Hour 162 

31/28

850 -3

925

-3

.2

 

.4 falls = 4 inches of snow .

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You're totally wrong

 

You are correct (and I know you know that, lol - this is for other folks) - ratios are mostly determined by snow crystal habit, which is driven by supersaturation levels in the dendritic growth zone, wherein supercooled water droplets nucleate as micro ice crystals on heterogeneous seed particles (dust usually) and then crystal growth on the initial ice crystals occurs via vapor phase deposition (where vapor condenses on the crystal surface and immediately freezes or goes directly from the vapor to the solid phase).  The intial nucleation events of ice crystals only occurs when the temperature is <-10C and occurs more easily as the temperature is even colder (greater supercooling which drives the phase change, or nucleation, to form solid crystalis).  

 

This vapor phase deposiiton is a function of vapor supersaturation, which is a function of temperature (and pressure) and the vertical velocities that move relatively warm/saturated air up to cold zones where that vapor becomes supersaturated (and the liquid droplets become supercooled, leading to the nucleation - both processes are going on at the same time).  Crystal growth occurs best around -15C and also is more efficent at reduced pressure, i.e., up around 500 millibars).  With relatively high supersaturation one tends to get better dendrites (I don't know why that is, but I can tell you it has something to do with the Gibbs Free Energy associated with the thermodynamic state of the crystal, which favors a particular crystal "habit"), which, upon reaching the ground "layer" better (think about the bulk density of popcorn vs. almonds, where bulk density is a function of shape and the amount of trapped air) than poorly grown/shaped crystals, giving a greater bulk density (more snow depth per unit volume of liquid).  

 

Made a few edits from the original as I was writing this from a pharmaceutical crystallization perspective, overlaid with what I've learned over the past few years about snow microphysics, which is quite similar.  

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