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February 4th-6th Storm Threat Discussion


Sn0waddict

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I think there will be a lot more sleet and ice pellets than people realize. Fortunately for us, sleet doesn't have nearly as high of an impact as freezing rain does. 

 

I'm not trying to take away from the ZR threat completely, but a lot of the short term models are now showing a prolonged period of IP as well. 

You're referring to eastern areas correct? Places like Warren County look bad.

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Snow line is collapsing near Allentown as the atmosphere wet bulbs.

Look at Dual Pol.

 

Nice catch. This was very well modeled. The HRRR and all other short term models show a marginally supportive area for snow developing from Staten Island's latitude northward over the next 1-3 hours. This should allow for some light accumulations before the mid level warming begins.

 

Dual pol shows this very well with the area supportive of snow collapsing southward over the last half hour.

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How far north does the freezing rain have to make it before we sound the alarms?

Wasn't most of that modeled though ? The areas that aren't snow we're not supposed to really snow. As William said, latitude will really matter with this one, and luckily we have that over many areas near Philly

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Nice catch. This was very well modeled. The HRRR and all other short term models show a marginally supportive area for snow developing from Staten Island's latitude northward over the next 1-3 hours. This should allow for some light accumulations before the mid level warming begins.

Dual pol shows this very well with the area supportive of snow collapsing southward over the last half hour.

Allentown is now snowing.

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You're referring to eastern areas correct? Places like Warren County look bad.

 

So long as the warm layer is not very "wide" in depth, these things will fall as ice pellets and sleet. The model precipitation type algorithms actually pick up on this now -- even though a sounding still gives you the best idea. The actual, literal freezing rain with ice accretion will fall in an area where this is a deepening warm layer aloft and a cold surface..and where moderate precipitation rates allow the ice to accrete. 

 

The orange on the 4km NAM is ice pellets and not freezing rain.

 

http://www.meteo.psu.edu/~fxg1/NAMSFC4_0z/cld11.gif

 

The warm layer widens and the surface remains cold and so the area of freezing rain eventually expands:

 

http://www.meteo.psu.edu/~fxg1/NAMSFC4_0z/cld14.gif

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So long as the warm layer is not very "wide" in depth, these things will fall as ice pellets and sleet. The model precipitation type algorithms actually pick up on this now -- even though a sounding still gives you the best idea. The actual, literal freezing rain with ice accretion will fall in an area where this is a deepening warm layer aloft and a cold surface..and where moderate precipitation rates allow the ice to accrete. 

 

The orange on the 4km NAM is ice pellets and not freezing rain.

 

http://www.meteo.psu.edu/~fxg1/NAMSFC4_0z/cld11.gif

 

The warm layer widens and the surface remains cold and so the area of freezing rain eventually expands:

 

http://www.meteo.psu.edu/~fxg1/NAMSFC4_0z/cld14.gif

I get what you're saying. WAA is usually under modeled. It would be a personal first to see that much pure sleet fall.

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The NAM is still showing dynamic cooling near NYC and north at the 850 mb level. You can observe it on this loop..heavier precipitation kicks down the warm air advection before it eventually wins out.

http://www.meteo.psu.edu/~fxg1/NAMSFC4_0z/8loop.html

Even though the NAM makes the most sense (history of these types of things),

I can not ignore that the Rgem, Ukmet, Gfs, Hrrr and Rap all have a solid 3"-6"+ snowfall down to NYC's boroughs.

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Increasing evidence to indicate that much of NYC & Long Island will see at least 6 new inches of snow by 12z / 7AM tomorrow morning.

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Nice catch. This was very well modeled. The HRRR and all other short term models show a marginally supportive area for snow developing from Staten Island's latitude northward over the next 1-3 hours. This should allow for some light accumulations before the mid level warming begins.

 

Dual pol shows this very well with the area supportive of snow collapsing southward over the last half hour.

Never have I been so unsure what will happen, people and mets are all over theplace; NYC mets consistently calling for 3-6 of snow in the city, no one here is saying that, before a switch to sleet and ZR. Others here say ZR for most areas, some call for sleet. I have my generator working and bought some gas. The schools are closed.  God help us all.

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I get what you're saying. WAA is usually under modeled. It would be a personal first to see that much pure sleet fall.

 

The WAA can be under modeled and there can still be sleet. See VDay 2007. But I think the depth of the cold air near the surface being more shallow suggests there will in fact be a significant threat for freezing rain west of NYC. 

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Hot off the presses from Mt. Holly

 

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
 

-- Changed Discussion --

THIS IS NOT GOING WELL. VERY LITTLE SNOW IS OCCURRING IN OUR CWA AND WE ARE ALREADY GOING OVER TO FREEZING RAIN NEAR THE LOWER SUSQUEHANNA VALLEY. HOPE IS AS INTENSITY INCREASES, WE LOSE SOME OF THE WARM AIR TEMPORARILY ABOVE 850MB AND GET SOME SLEET VS FREEZING RAIN. LOOSELY THIS BOUNDARY IS CLOSE TO ABOUT A 545 1000-500MB THICKNESS AND 0C ISOTHERM AT 850MB WITH THAT WARMER AIR ALOFT. WE HAVE SCALED BACK THE SNOW AND INCREASED THE ICE ACCUMULATIONS. BASED ON THE LATEST MESOSCALE MODELS HOLDING ONTO TO THE 32F LONGER NORTHEAST, WE WILL ADD WESTERN MONMOUTH COUNTY TO THE WARNING.

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Even though the NAM makes the most sense (history of these types of things),

I can not ignore that the Rgem, Ukmet, Gfs, Hrrr and Rap all have a solid 3"-6"+ snowfall down to NYC's boroughs.

 

It is really bizarre to see all of the short term/high resolution models showing so much snow. I will say though, the HRRR has trended northward and warmer yet its algorithms keep showing a lot of snow. It may be a combination of the model using sleet as snowfall, and a lack of compensation for mid level warming.

 

To be honest...I would really be shocked if any NYC reporting station came in with 3" or more. But to see all of the high resolution models show that much snow accumulated on the front end is pretty surprising. The most surprising of all is the RGEM's 15mm. 

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Craig Allen going quite bullish! From his Facebook minutes ago:

 

"My pillow awaits and my brain hurts already.
Quick update based on 0z products.

>Snow to sleet to freezing rain for much of the area. Possibly plain rain along the NJ shore and immediate south shore and east end of L.I. earlier and for awhile longer.

> Snow amounts a little lower. Back to the 1-3" for shoreline. 2-4" around City but 4-8" from Bronx north, GWB west and from US15 in CT on north. 8-12" possible up beyond I-84.

> While snow amounts a couple inches lower, ice accretion is increased. There is now a possibility of 1/4 to 1/2"+ ice on all trees and power lines. May not sound like much but that is huge and heavy. reminds me of a wicked ice storm when I was growing up in Massapequa in the 70's. This may be our worst ice storm in over 2 decades for some areas.

> Sleet may be primary precip for a few hours as well as the atmosphere battles it out. Don't even be surprised by some thunder. Latest dynamics for the morning are incredibly high and volatile for a winter system.

>I just can't see many business or schools being opened. if they are, you might be nuts trying to get to them if this pans out based on latest data.
"

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The WAA can be under modeled and there can still be sleet. See VDay 2007. But I think the depth of the cold air near the surface being more shallow suggests there will in fact be a significant threat for freezing rain west of NYC. 

you forgot NYC and Long Island, the models are showing significant ZR for us too. Looks like .50-.75 ZR after the initial snow and sleet period.  We look to have ice storm warning criteria... Please show me otherwise....

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Hot off the presses from Mt. Holly

 

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...

 

-- Changed Discussion --

THIS IS NOT GOING WELL. VERY LITTLE SNOW IS OCCURRING IN OUR CWA AND WE ARE ALREADY GOING OVER TO FREEZING RAIN NEAR THE LOWER SUSQUEHANNA VALLEY. HOPE IS AS INTENSITY INCREASES, WE LOSE SOME OF THE WARM AIR TEMPORARILY ABOVE 850MB AND GET SOME SLEET VS FREEZING RAIN. LOOSELY THIS BOUNDARY IS CLOSE TO ABOUT A 545 1000-500MB THICKNESS AND 0C ISOTHERM AT 850MB WITH THAT WARMER AIR ALOFT. WE HAVE SCALED BACK THE SNOW AND INCREASED THE ICE ACCUMULATIONS. BASED ON THE LATEST MESOSCALE MODELS HOLDING ONTO TO THE 32F LONGER NORTHEAST, WE WILL ADD WESTERN MONMOUTH COUNTY TO THE WARNING.

some of those areas did indeed switch to snow

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Craig Allen going quite bullish! From his Facebook minutes ago:

 

"My pillow awaits and my brain hurts already.

Quick update based on 0z products.

>Snow to sleet to freezing rain for much of the area. Possibly plain rain along the NJ shore and immediate south shore and east end of L.I. earlier and for awhile longer.

> Snow amounts a little lower. Back to the 1-3" for shoreline. 2-4" around City but 4-8" from Bronx north, GWB west and from US15 in CT on north. 8-12" possible up beyond I-84.

> While snow amounts a couple inches lower, ice accretion is increased. There is now a possibility of 1/4 to 1/2"+ ice on all trees and power lines. May not sound like much but that is huge and heavy. reminds me of a wicked ice storm when I was growing up in Massapequa in the 70's. This may be our worst ice storm in over 2 decades for some areas.

> Sleet may be primary precip for a few hours as well as the atmosphere battles it out. Don't even be surprised by some thunder. Latest dynamics for the morning are incredibly high and volatile for a winter system.

>I just can't see many business or schools being opened. if they are, you might be nuts trying to get to them if this pans out based on latest data."

Oh dear. My word. One met calling for more snow ( Gregory ) another of equal stature calling for less, with more ice. Well, I'm hoping for sleet. Talk about extreme weather.

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