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DISCUSSION ONLY: Snow/rain/slopfest potential Tuesday 11/27/2012

famartin

By famartin,
in Philadelphia Region

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famartin

famartin

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NAM bullseye has shifted east since this morning. Nice hit for central Jersey and PA roughly from turnpike to I-78. Mostly rain down here in S Chester County over to PHL and east.

The NAM really shoves in the warm air at the low levels around PHL. It is indeed mostly rain there.

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Thunder Road

Thunder Road

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Dummy question: Is it possible to have snow falling with the Environmental Temp and Wet Bulb Temp both > 0 C? I thought no, but the BUFKIT for KPNE says "snow" based on whatever algorithm it uses. (Specifically, I'm looking at 17z tomorrow off the 0z NAM for KPNE.)

Speaking of the 0z NAM, KPNE picks up 0.658" total QPF. Ignoring its precip type output and adding up only when Wet Bulb Temp < or = 0 C, only 0.143" of that is snow. For the rest, you have Dew Points > or = 0.1 C, so by definition Wet Bulb Temps must also be above freezing. So throw in crappy ratios and a wet model bias, and you end up with an inch if you're lucky at Northeast Philly.

Of course, all of this is only true if I'm not putting too much emphasis on the role of Wet Bulb Zero...

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famartin

famartin

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Dummy question: Is it possible to have snow falling with the Environmental Temp and Wet Bulb Temp both > 0 C? I thought no, but the BUFKIT for KPNE says "snow" based on whatever algorithm it uses. (Specifically, I'm looking at 17z tomorrow off the 0z NAM for KPNE.)

Speaking of the 0z NAM, KPNE picks up 0.658" total QPF. Ignoring its precip type output and adding up only when Wet Bulb Temp < or = 0 C, only 0.143" of that is snow. For the rest, you have Dew Points > or = 0.1 C, so by definition Wet Bulb Temps must also be above freezing. So throw in crappy ratios and a wet model bias, and you end up with an inch if you're lucky at Northeast Philly.

Of course, all of this is only true if I'm not putting too much emphasis on the role of Wet Bulb Zero...

Depends on how large an area is above WBZ, and how far above. But yes, snow can fall in above zero wet bulb air if its not too far above and/or for a long distance. Once the WBZ is above zero snow definitely starts melting.

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Thunder Road

Thunder Road

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Depends on how large an area is above WBZ, and how far above. But yes, snow can fall in above zero wet bulb air if its not too far above and/or for a long distance. Once the WBZ is above zero snow definitely starts melting.

I see. Thanks. So a Wet Bulb Temp of 0.1 C for roughly 500-1000 meters is not killer then, correct?

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famartin

famartin

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I see. Thanks. So a Wet Bulb Temp of 0.1 C for roughly 500-1000 meters is not killer then, correct?

Define killer. Will snow be melting at the bottom of that column? Absolutely. Will it be all gone? Maybe not. Remember, if the wetbulb is 0.1C, what's the air temp? 1C? Yes, the snow will be melting. Maybe not gone, but not all snow either. Probably rain/snow mix.

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