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Feb 12-13 Sleet/Snow/ZR Event


JoshM

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You can't take modeled fzra a face value. Fzra is a self limiting process and it needs continuous reinforcement of cold air to keep accumulating. With the transient parent high Wed...the cold air will not be reinforced enough to offset the latent heat of freezing in the sfc layer. I took a cursory look at some consensus qpf across the Midlands and noted the timing is about 4-5 hrs with sub-freezing sfc temps leading to around 0.3-0.4 ice accum before the transition to rain occurs around 14Z or so. Still a sigfnt and damaging ice potential tho.

Hey scott, I have a question:

Is there a number attached to the phrase "heavy snowfall accumulations in a text grid fxcast?

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You can't take modeled fzra a face value. Fzra is a self limiting process and it needs continuous reinforcement of cold air to keep accumulating. With the transient parent high Wed...the cold air will not be reinforced enough to offset the latent heat of freezing in the sfc layer. I took a cursory look at some consensus qpf across the Midlands and noted the timing is about 4-5 hrs with sub-freezing sfc temps leading to around 0.3-0.4 ice accum before the transition to rain occurs around 14Z or so. Still a sigfnt and damaging ice potential tho.

Yep I know all about the self limiting nature of freezing rain . Gary Lackman who wrote a great paper on that was my advisor.

Keep in mind up here at RDU we are being reenforced by diabetic processes (hybrid cad) hence it would take longer to warm to 32-33. So damaging ice would occur if the nam were literally right.

With that said it is a model forecast of freezing rain so I take it with caution for no other reason than that .

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The GFS drops .75 of liquid and it’s all snow imby: confirmed with soundings.  This is probably about the best solution in terms of snowfall total for my backyard.  

 

I think if you live from atlanta to Charlotte, you should be rooting for the GFS, unless you would rather have sleet.

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Hey scott, I have a question:

Is there a number attached to the phrase "heavy snowfall accumulations in a text grid fxcast?

 

Yeah it has to do with the rate of snowfall...I can't recall the exact rate right now, but I think it's around 2" per hr.  

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Yep I know all about the self limiting nature of freezing rain . Gary Lackman who wrote a great paper on that was my advisor.

Keep in mind up here at RDU we are being reenforced by diabetic processes (hybrid cad) hence it would take longer to warm to 32-33. So damaging ice would occur if the nam were literally right.

With that said it is a model forecast of freezing rain so I take it with caution for no other reason than that .

 

I'm sure you do. I was just using your post as an example of why this storm wont output around an inch of ice, like some folks think it may.   

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The CIPS analog probabilities for 6 or more of snowfall have increased, up to 30% over the mountains and I-40 corridor in the western and central parts of NC, looks like the 15% prob runs along I-85. Some good analog years in the mix.

 

Edit: Actually the 30% prob line runs along I-85, and slowly increases as you head NW.

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