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WeatherFox

01/02/14 to 01/03/14 Snow Storm Observations

1,693 posts in this topic

Any obs from Manhattan. Heading into the city, roads looking ok?

*looks out window

Still light, but starting to stick on amsterdam in UWS.

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A few folks have asked about snow ratios and what affects snow ratios.  I'm not a meteorologist, but I am an expert in nucleation/crystallization phase changes (in the chemical/pharmaceutical industry, but the concepts apply almost exactly to snow). 

So, for those who are curious why our snow ratios will be so high (15-20:1, which means 0.5" of liquid gives 7.5-10" of snow, instead of the usual 5" of snow in a typical 10:1 ratio), conditions are expected to be very favorable for large, dry, fluffy snow crystals in the primary snow growth region (around 700 mb of pressure, several thousand feet up in the atmosphere).  Hope what follows helps. 

 

Specifically, as relatively warm, moist air saturated with water vapor is lifted into the 700 mb region, which will be very cold, relatively speaking vs. "typical" snowstorms, i.e., temps will be about -10 to -22C at that level, this will lead to that water vapor becoming highly superaturated, meaning the relative humidity of that parcel of air at that temperature actually well exceeds 100%, which denotes being supersaturated, i.e., beyond 100% saturation; thermodynamically, this situation cannot exist for long, as that supersaturated vapor wants to either condense into liquid or directly condense into frozen particles, depending on the temp (and pressure). 

 

This supersaturation leads to very fast snow crystal nucleation (the creation of snow crystals at those cold temps aloft), followed by good dendritic snow growth (via vapor phase deposition - the water vapor that remains supersaturated in the parcel essentially changes phases from vapor to ice, as it crystallizes and grows directly on the "starter crystals" that just nucleated) on those crystals, leading to dendrites and plates.  These dendtrites and plates "layer" better on the ground, such that there is more air present in the snow on the ground, resulting in a lower bulk density (low mass per unit volume) of that snow or a greater snow depth to liquid equivalent ratio.  Think of a pile of dry leaves vs. a pile of wet, aged leaves, in which the dry leaves contain ar less leaves and far more air per unit volume vs. wet leaves. 

 

To get powdery, fluffy, low bulk density snow, one needs both conditions, though: cold temps in the snow growth region, plus good vertical lift to drive the supersaturation - it's the vertical lift which carries warm, relatively moist air from the surface (or near the surface) up into the primary snow growth region around 700 mb (to be sure, supersaturation and nucleation/crystallization occur at more heights than 700 mb - it's just that the 700 mb region is the "standard" referred to), which leads to the supersaturation and at the right temps, the good plates/dendrites form and grow.  See the link for the pics of the crystals one typically gets at various temps in the snow growth region. 

 

Why -10 to -22C in the snow growth layer leads to plates and dendrites vs. rods or cubes is unclear to me.  Perhaps that's something I should look into...

 

http://stream2.cma.gov.cn/pub/comet/MountainMeteorology/SnowpackandItsAssessment/comet/afwa/snowpack/media/graphics/habits.jpg

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it looks a lot better at this point than I thought it would.

That radar's amazing so far-I thought this storm would produce more than models showed with the dynamics it has and it just might. It would be even better if we get more backbuilding tomorrow morning to keep snow falling through 8-9am or so. But those inverted troughs are very hard to guess at. But judging by the radar now, 8" looks definitely reachable and we have a shot at 10". And nice, fat flakes too.

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Can someone please explain the washboard ripple look on the echoes over central coastal jersey?

 

Strictly a guess on my part, but I think those waves are in an area where synoptic scale lift is overrunning the low level lift associated with the OES bands propagating in the opposite direction.  Coastal Monmouth looks to be an interesting place this evening.

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That radar's amazing so far-I thought this storm would produce more than models showed with the dynamics it has and it just might. It would be even better if we get more backbuilding tomorrow morning to keep snow falling through 8-9am or so. But those inverted troughs are very hard to guess at. But judging by the radar now, 8" looks definitely reachable and we have a shot at 10". And nice, fat flakes too.

 

im have a feeling some people on the jersey shore and S LI will report 12-15" (Not us  :hug: )

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its growing NE into lower manhattan and Brooklyn.

 

great start right now…..i love this storm already….

 

it also helps when the storm is forecast well and you get a uptick in qpf as you get closer.

 

also no rain/snow line watching 

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NYC is going to over perform and places farther west are going to pass through a dry slot...the banding consolidating over Monmouth is massive and pushing north while drier air moves into Central PA.

I feel bad for places around my old stomping grounds in central PA which looks to have gotten "jumped over" again. Happened time and time again when I lived out there. I was worried about that dry hole appearing up there again when models started insisting on a 1/22/05 type repeat of snow distribution-a lot over the southern tier of NY over towards our area and New England, and a lot less there.

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I feel bad for places around my old stomping grounds in central PA which looks to have gotten "jumped over" again. Happened time and time again when I lived out there. I was worried about that dry hole appearing up there again when models started insisting on a 1/22/05 type repeat of snow distribution-a lot over the southern tier of NY over towards our area and New England, and a lot less there.

One of DT's cardinal rules: Someone always gets screwed in a Miller B.

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A few folks have asked about snow ratios and what affects snow ratios.  I'm not a meteorologist, but I am an expert in nucleation/crystallization phase changes (in the chemical/pharmaceutical industry, but the concepts apply almost exactly to snow). 

So, for those who are curious why our snow ratios will be so high (15-20:1, which means 0.5" of liquid gives 7.5-10" of snow, instead of the usual 5" of snow in a typical 10:1 ratio), conditions are expected to be very favorable for large, dry, fluffy snow crystals in the primary snow growth region (around 700 mb of pressure, several thousand feet up in the atmosphere).  Hope what follows helps. 

 

Specifically, as relatively warm, moist air saturated with water vapor is lifted into the 700 mb region, which will be very cold, relatively speaking vs. "typical" snowstorms, i.e., temps will be about -10 to -22C at that level, this will lead to that water vapor becoming highly superaturated, meaning the relative humidity of that parcel of air at that temperature actually well exceeds 100%, which denotes being supersaturated, i.e., beyond 100% saturation; thermodynamically, this situation cannot exist for long, as that supersaturated vapor wants to either condense into liquid or directly condense into frozen particles, depending on the temp (and pressure). 

 

This supersaturation leads to very fast snow crystal nucleation (the creation of snow crystals at those cold temps aloft), followed by good dendritic snow growth (via vapor phase deposition - the water vapor that remains supersaturated in the parcel essentially changes phases from vapor to ice, as it crystallizes and grows directly on the "starter crystals" that just nucleated) on those crystals, leading to dendrites and plates.  These dendtrites and plates "layer" better on the ground, such that there is more air present in the snow on the ground, resulting in a lower bulk density (low mass per unit volume) of that snow or a greater snow depth to liquid equivalent ratio.  Think of a pile of dry leaves vs. a pile of wet, aged leaves, in which the dry leaves contain ar less leaves and far more air per unit volume vs. wet leaves. 

 

To get powdery, fluffy, low bulk density snow, one needs both conditions, though: cold temps in the snow growth region, plus good vertical lift to drive the supersaturation - it's the vertical lift which carries warm, relatively moist air from the surface (or near the surface) up into the primary snow growth region around 700 mb (to be sure, supersaturation and nucleation/crystallization occur at more heights than 700 mb - it's just that the 700 mb region is the "standard" referred to), which leads to the supersaturation and at the right temps, the good plates/dendrites form and grow.  See the link for the pics of the crystals one typically gets at various temps in the snow growth region. 

 

Why -10 to -22C in the snow growth layer leads to plates and dendrites vs. rods or cubes is unclear to me.  Perhaps that's something I should look into...

 

http://stream2.cma.gov.cn/pub/comet/MountainMeteorology/SnowpackandItsAssessment/comet/afwa/snowpack/media/graphics/habits.jpg

Great post. This graphic may help, too. I'm not sure why dendrites tend to grow in the -12C to -18C region... and to be honest I'm not sure if the field fully understands it yet either.

morphologydiagram.jpg

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Snowing at a very good clip, but not as intense as I sometimes see in these types of bands. As the night goes on things should just get better and better though with growing ratios so this is a great start. 

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