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12/6-12/7 obs thread


Bostonseminole

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Looks like hvy precip will be a bit further south than modeled, looks like wxmanmitch to MpM riding N line maybe over to MHT later. Who knows just more weenie interpretation

Lets get hubb dave and Ashburnham poster to flip next hour for some real fun, that radar looks juiced in sw mass , also looks like plenty more to impact the nw ct over to hft tolland / orh corridor later. I am wondering if my area (10 miles n of bos) can dynamically cool down if that precip traverses us without weakening much

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Mixed precip all the way back to BGM. Must be some sneaky warm layer near 800mb. Surprised it hasn't mixed out in heavier echoes. What I see outside isn't pure sleet. Looks more like partially melted flakes that refroze in a colder layer.

ASOUT

 

I don't remember much talk of a sneaky warm layer for the southern tier of NY.  And it turns out that's not the problem at BGM.

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When you say lift is below that do you mean it isn't strong enough to get the water droplets into the snow growth zone?  sorry for noob question but I have zero understanding as to how this works...

When we talk about the snow growth zone usually what we mean is the temperature zone in the cloud that produces the best crystal growth which is the -12C to -18C layer. If you get a deep layer of those temps with saturation and good lift you'll start cranking out some large dendrites. You can still get snow growth outside of that temp zone, but you start seeing smaller dendrites or other crystal types.

 

The problem in those -RAPL areas is that cloud temps are mediocre to produce ice nuclei so like Scott said, you have mostly supercooled droplets precipitating via that lift.

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When we talk about the snow growth zone usually what we mean is the temperature zone in the cloud that produces the best crystal growth which is the -12C to -18C layer. If you get a deep layer of those temps with saturation and good lift you'll start cranking out some large dendrites. You can still get snow growth outside of that temp zone, but you start seeing smaller dendrites or other crystal types.

 

The problem in those -RAPL areas is that cloud temps are mediocre to produce ice nuclei so like Scott said, you have mostly supercooled droplets precipitating via that lift.

Thanks!

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The problem in those -RAPL areas is that cloud temps are mediocre to produce ice nuclei so like Scott said, you have mostly supercooled droplets precipitating via that lift.

It's a pretty interesting situation when you are getting sleet but it's not from melting and refreezing of flakes... super-cooled droplets falling and freezing on their way down, and then possibly melting right at the surface to form that RNPL mix. Don't see that too often.

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It's a pretty interesting situation when you are getting sleet but it's not from melting and refreezing of flakes... super-cooled droplets falling and freezing on their way down, and then possibly melting right at the surface to form that RNPL mix. Don't see that too often.

Usually when you see it it's brief and during WAA situations where you start torching the mid-levels, but there's a lingering cold dry layer around 875-925mb or something.

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lol this past page has made me LOL - well done everyone. 

 

Seems like things are on target. Snow growth issues on the northern fringe near ALB with sneaky warm layers causing issues even where it is 33F. I posted earlier that I thought this wouldn't be your typical "the boundary layer is killing us stuff" - rather a lot of mid level warmth that is in no hurry to leave. 

 

We are advecting a nice shot of cold from the sfc through 900 mb so we should continue to tickle the sleet south. 

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