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PHL CWA Feb 1-2 Storm OBS and Discussion


Rib

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18z NAM at KPNE has 0.47" with the 2m temp at 32.0°. I'm still waiting to for the 3-hourly to upload on WxCaster, but wow that could be crippling.

looks like very little snow but approx. 0.8" of the precip occurs with at least 975mb to the surface below freezing...not sure if that is deep enough for fr. rain but that would certainly make the situation more interesting

0.5" of the precip is definitely rain though

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Looking at soundings, all layers below 900mb are below freezing for the Lehigh Valley at 42. Sleet?

That may be your saving grace. With the storm trending colder, I think for a while Wed morning the LV will be seeing sleet, while the area between 78 and 276 will be seeing ZR. That's why i think the highest ice amounts (up to 3/4") will be in upper Bucks and upper Montgomery, with less as you head south and north.

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looks like very little snow but approx. 0.8" of the precip occurs with at least 975mb to the surface below freezing...not sure if that is deep enough for fr. rain but that would certainly make the situation more interesting

0.5" of the precip is definitely rain though

based off 2m temps, 0.21 falls as ZR at PNE from Round 2. However, another 0.49 falls with the 2m temp rising to 32.9° at the end of the 3-hour period. So I would say 0.10-0.20 of that may also still be ZR. Also, 975's and 950's are still below freezing at that hour (hr 42) although by hr 45 we're above freezing from the surface up.

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The difference between BING and MT HOLLY snow maps is comical/laughable for the port jervis areas....mt holly has 9 inches possible, bing has less than 2.5...

is there no dialouge between the two agencies? that's rediculous.

Just saying.

Must have been an old map; Bing map now has much larger snowfall amounts with 8" or more in their SE counties: http://www.erh.noaa.gov/bgm/winter/stormtotal/stormtotalsnow.php

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Anyone of the most recent soundings for KAVP and KMPO. Hoping for more a sleet signature. If they are posted, can someone provide an explanation of them?

18z NAM

devistating ice storm

post-2206-0-35124300-1296516780.png

3" of snow

1/2" of sleet

and 9/10" of Frz rain

no rain

18z GFS

post-2206-0-97333200-1296516830.png

6" of snow

3/4" of sleet

1/2" of fz rain

a touch of rain

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Maybe a pro met can chime in, but if the rain is heavy enough, perhaps there will be more run-off as opposed to ice accruing on trees and power lines. I know I'm probably reaching, just trying to be optimistic.

Could be both...street flooding and icy spots mixed in FTL...

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Looking at soundings, all layers below 900mb are below freezing for the Lehigh Valley at 42. Sleet?

It comes down to the depth/strength of the warm layer, and whether it can fully melt all solid parts into a rain drop. If that happens, and the bottom cold layer is never below -8ºC, then you will maintain a supercooled droplet since it cannot form back into a solid. If a little solid ice makes it through the warm layer, then whatever part has melted to liquid can refreeze around that into a sleet pellet when its below 0ºc. In the case where it fully melts in the warm layer to a droplet, it can refreeze into an ice pellet only if the surface cold layer reaches below -8ºc (pretty rare in these setups).

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That's doesn't sound good at all. This may sound like a stupid question but with that amount of ZR what does that mean in ice thickness 1/4 to 1/2 inch or less?

It's close enough to 1:1, although I'm not totally sure. One source said 1.25:1.

So it would put us close to 1/2"

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http://www.erh.noaa....i/hist_phi.html

...1994...

A great ice storm commenced on the 7th and extended into the 8th. Low pressure formed east of Wyoming on the 5th, moved to the Central MS Valley on the 6th, reached Ern KY the morning of the 7th and redeveloped along the Ern VA coast on the morning of the 8th. A strong high pressure system remained nearly stationary over Ontario Province, Canada and continued to pump in a fresh supply of cold air near the ground. This kept temperatures below freezing throughout this event resulting in one of the worst ice storms on record for SE PA. The freezing rain started lightly the morning of the 7th, but in spite of this, all roadways were glazed by the start. As rain increased in intensity the night of the 7th, the accumulation of ice started to down tree limbs and power lines. Ice accumulations were 1/4" to 1/2" across most of SE PA, but amounts reached up to 1" in the NW PHL suburbs. While there were 5,000 customers without power in the Lehigh valley, the hardest hit area was around PHL. Approximately 590,000 Philadelphia Electric Company (PECO) customers lost power. This represents about 40% of their customers and was the worst power outage in PECO's history, surpassing the 400,000 customers who lost power during the heavy wet snowstorm on Mar 20, 1958. Approximately 150,000 (of 232,000) customers lost power in Delaware Co, 134,000 in Bucks Co, 112,000 in Chester Co, 105,000 in Montgomery Co and 89,000 in Philadelphia Co. As of Sunday morning the 9th, 123,000 customers still did not have power. Full power was not restored until Tuesday morning the 11th. There were literally thousands of ice-related vehicular accidents and described as "countless" number of personal injuries resulting from slipping on the ice. Miraculously no one was directly killed as a result of this ice storm. In addition to damage to electrical lines, the ice accumulation on fruit trees brought a significant amount of damage. (SD)

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I am more of a reader than poster, but i have a question I have been curious about. Does anyone know anything about sleet ratios? In other words, 1 inch of QPF would be about how much sleet? I have a pretty good grasp of snow ratios dealing with temps in the snow growth region and dendrite strength, but I've never heard anything about sleet ratios. Any help is appreciated!

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I am more of a reader than poster, but i have a question I have been curious about. Does anyone know anything about sleet ratios? In other words, 1 inch of QPF would be about how much sleet? I have a pretty good grasp of snow ratios dealing with temps in the snow growth region and dendrite strength, but I've never heard anything about sleet ratios. Any help is appreciated!

I'm no expert, but I think 3:1 is normal.

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I am more of a reader than poster, but i have a question I have been curious about. Does anyone know anything about sleet ratios? In other words, 1 inch of QPF would be about how much sleet? I have a pretty good grasp of snow ratios dealing with temps in the snow growth region and dendrite strength, but I've never heard anything about sleet ratios. Any help is appreciated!

i believe its 3:1 ratio.

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