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NYC CWA Feb 1-2 Storm Discussion


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I posted that 8 posts ago.

So the .50"-.75" that falls thru hour 42 is not significant icing?

I still dont understand your point.

point- there will be no ice accretion on anything other than trees and cars with temps "around" freezing. Just my opinion...you need temps to be in the low 20 to mid 20's to get a real dangerous ZR situation...especially in the city

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yeah- you have no idea how many times i tried to get closer!

either way, if the NAM is right we are going to have serious flooding issues...unfortunately our snowpack is going to take a very large hit

I think if it's only 1" or less of liquid rain, the snow should eat most of it up unless temps really surge past 40. If it stays 35 or so, not much snow will melt, even with the rain. It just soaks it all in and then freezes solid when the cold air rushes back in.

We need to watch that on future model runs, because there will certainly be a coastal front zone likely where the wind shifts direction to more E or ESE. It could go from 35 to 45 very easily if that front passes. That's when real flooding problems become likely.

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They are much more likely to issue warnings with serious icing than even a 3 to 6" snowfall. Even with the NAM there is a lot of precip falling with surface temps at or below freezing. I also don't think they should base a forecast on one run of the NAM which has been wildly inconsistent all winter.

I dont think they took into consideration the NAM before their disco. I think they are going bullish so people dont get caught off guard and more for the ice than anything else. I think its unlikely that Central Jersey gets the 2-4 they are forecasting. There should be some sort of special ice advisory I think that makes more sense in situations like this

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Intensity of the precipitation combined with the temperature of the rain thats falling. if the air is +5C (41F) 3-5,000 feet above the ground, it may only cool one or two degrees before it hits the surface, not giving it enough time on cooled surfaces such as trees and powerlines to freeze before it runs off. If the warm layer were thinner or cooler, we would see much more accretion, but the strength of the warm air advection is just too strong.

You don't think a cold layer of that depth (and significance - look at how cold the air is just above the surface on earthlight's sounding) would be enough to supercool a drop? Don't forget all the thermal energy goes into melting a snowflake - only once it is completely melted will the temperature of the raindrop begin to rise. I just don't think it'd be that much of an issue... I doubt the raindrop is going to warm to a full 40F or something. I assume it will be near freezing to begin with.

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point- there will be no ice accretion on anything other than trees and cars with temps "around" freezing. Just my opinion...you need temps to be in the low 20 to mid 20's to get a real dangerous ZR situation...especially in the city

We already have some significant tree damage in spots in Long Beach because of the 16" of very wet snow sticking to everything. If we tack on ice and sleet, I see power outages becoming a real concern along with more tree damage, even if we go to rain. Again, if it only rises to 35 or so, not much will melt.

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point- there will be no ice accretion on anything other than trees and cars with temps "around" freezing. Just my opinion...you need temps to be in the low 20 to mid 20's to get a real dangerous ZR situation...especially in the city

Temps are 26-29 for the .50"-.75" of liquid.

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point- there will be no ice accretion on anything other than trees and cars with temps "around" freezing. Just my opinion...you need temps to be in the low 20 to mid 20's to get a real dangerous ZR situation...especially in the city

well i agree with this. I don't expect much ice accretion on blacktops...but it will be an issue on trees and powerlines especially in the suburbs.

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I dont think they took into consideration the NAM before their disco. I think they are going bullish so people dont get caught off guard and more for the ice than anything else. I think its unlikely that Central Jersey gets the 2-4 they are forecasting. There should be some sort of special ice advisory I think that makes more sense in situations like this

that's for the lower portion of the warning where criteria is only 0.25". Up here in Morris County where criteria is 0.50" they still went with a WSW. I suspect, that sometime on Tuesday night the WSW will be replaced by Ice Storm Warnings. :arrowhead:

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You don't think a cold layer of that depth (and significance - look at how cold the air is just above the surface on earthlight's sounding) would be enough to supercool a drop? Don't forget all the thermal energy goes into melting a snowflake - only once it is completely melted will the temperature of the raindrop begin to rise. I just don't think it'd be that much of an issue... I doubt the raindrop is going to warm to a full 40F or something. I assume it will be near freezing to begin with.

Good post. Just because the air temperature reaches a certain level does not mean the object passing through that warm layer has that temperature as well.

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Wow, Upton is going pretty bullish down to the immediate burbs.

Either they expect the thermal profiles to be colder for round 2 or they think the precip shield for round 1 will be farther south than depicted in the latest runs.

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Generally speaking yes but the ground can be colder than the air temperature or like in cases in urban areas, warmer. I think thats why you rarely see freezing rain events in Manhattan. I think it would have to be raining below 27 or 28 to get severe icing in the city

it's plain and simple..if it raining and it is below 32 degrees..it is freezing rain, or am I missing something?

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Good post. Just because the air temperature reaches a certain level does not mean the object passing through that warm layer has that temperature as well.

Sure, but it becomes more difficult to cool the rain droplets as the warm layer becomes deeper. It may not be 40 F, but it's probably warm enough to avoid significant icing especially in the city where temperatures rise above freezing for a good period on the NAM, even during the heavy precipitation. Also, it's important to keep in mind the NAM is the coldest amongst guidance...and has a tendency to be too cold in these types of events.

f45.gif

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Wow, Upton is going pretty bullish down to the immediate burbs.

Actually stating that eastern Long Island will have more icing than western LI (although not by much .10-15, but notable nonetheless), which is a bit bizarre, unless they are taking into account the urban effect of roads/sidewalks being treated.

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That Upton map has me around .3 of ice....that would warrent more than a WWA, which we all know nobody takes seriously.

sorry but warning criteria ice for LI is 0.5". With that being said, I've seen warnings before where they went with a warning for the combo of ice and snow. The ice is still 24 hrs away though, and it looks like LI doesn't get much snow so I would say WWA is the way to go now with a possible upgrade tomorrow.

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Actually stating that eastern Long Island will have more icing than western LI (although not by much .10-15, but notable nonetheless), which is a bit bizarre, unless they are taking into account the urban effect of roads/sidewalks being treated.

The same thing happened in VD07. The winds will remain more northerly in nature the further east you go for a longer period of time in a setup like this.

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Sure, but it becomes more difficult to cool the rain droplets as the warm layer becomes deeper. It may not be 40 F, but it's probably warm enough to avoid significant icing especially in the city where temperatures rise above freezing for a good period on the NAM, even during the heavy precipitation. Also, it's important to keep in mind the NAM is the coldest amongst guidance...and has a tendency to be too cold in these types of events.

f45.gif

I also agree that with a deep enough warm layer the droplets will require more time to solidify and/or recool to freezing. And, with temps being near 32 degrees, not much ice accretion will occur on roadways and other "warmer" surfaces. However, prior to that warm frame you posted, temperatures are quite cold at the surface and the warm layer is not as large. Couple that with the fact that the ground has an enormous snowpack, and you wind you with decent ice accretion, at least for a while.

Some anecdotal evidence: last week when the temperatures were holding in the mid to upper 30's in the evening, puddles that had formed during the day were already freezing solid, especially those that were right around snow The key here is is that it wasn't a radiational cooling night either.

I doubt areas in Manhattan will get accumulating freezing rain, but then again Manhattan is the last place I would go to for winter weather.

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it's plain and simple..if it raining and it is below 32 degrees..it is freezing rain, or am I missing something?

Overall yes, but there are certain things that can cause the rain to not freeze. If the temperatures are only marginally below 32F, the latent heat released from the raindrop freezing can warm up the surrounding air and reduce further freezing (a sort of negative feedback). Plus blacktops can be warmer than the air temperature, etc. Plus as was being discussed/debated, the raindrop may not have time to supercool between the warm layer and the surface. If that were the case the raindrop would remain liquid and roll off of surfaces and freeze the normal way instead of directly freezing upon contact.

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sorry but warning criteria ice for LI is 0.5". With that being said, I've seen warnings before where they went with a warning for the combo of ice and snow. The ice is still 24 hrs away though, and it looks like LI doesn't get much snow so I would say WWA is the way to go now with a possible upgrade tomorrow.

0.5 ice is quite a lot, if that were to ever happen.....forget about warnings,THAT would be disaterous....

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Overall yes, but there are certain things that can cause the rain to not freeze. If the temperatures are only marginally below 32F, the latent heat released from the raindrop freezing can warm up the surrounding air and reduce further freezing (a sort of negative feedback). Plus blacktops can be warmer than the air temperature, etc. Plus as was being discussed/debated, the raindrop may not have time to supercool between the warm layer and the surface. If that were the case the raindrop would remain liquid and roll off of surfaces and freeze the normal way instead of directly freezing upon contact.

In State College it often took temps of 30 or lower to really start freezing rain because of the blacktop and heated sidewalks on campus. The higher uphill you went, the more ice always accreted. Wednesday though looks like it could be a major icestorm there. I saw tons of sleet there but only a couple of major freezing rain events.

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