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12/7-12/8 Potential Event Discussion Part II

earthlight

By earthlight,
in New York City Metro

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eduggs

eduggs

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This is why I kept beating into the ground the point that this storm was highly unlikely to begin with...and that even a slight change in the upper air pattern would screw us because the surrounding pattern is terrible.

Normally we have some wiggle room but in this situation we don't. And that was the point myself and a few others were trying to drive home a few days ago.

I usually agree with you, and I rely on your posts for lots of info, but I don't like this explanation. I can't remember any storm where there was much wiggle room for the NYC metro. We don't live in a good location for snow. We're relatively far NW, yet still right along the ocean. When the NAO is negative, we often get suppression. When the PNA is positive, sometimes a trof amplifies too fast and strong and a storm cuts inland. The marine influence doesn't help with any kind of low level southeasterly flow. When both indices are favorable and the EPO and AO are also negative, sometimes a mid-level southerly flow sets up and we get ice. Other times the baroclinicity is weak and/or there is no triggering shortwave/PVA.

I don't think the "pattern" is to blame for some of the guidance suggesting a NYC snowstorm and then taking it away. I'm very much against the generalized characterization of atmospheric flow into numbers. I think it's best left as a tool for climatologists. The pattern doesn't dictate the weather. Rather, the weather - the movement of air in the atmosphere - determines how we characterize the pattern. When you watch your breath on a cold morning as you exhale, sometimes it swirls one way, sometimes another. It's chaotic motion - random and unpredictable. Snowstorms are hard to come by around here. We've had warm weather since October and one major snowstorm just west of the metro. Now it looks like another near miss. That's way better than average for this time of year. I think it's lazy to say that if the NAO was negative we'd get a snowstorm. That's kind of like saying if it were colder it would be snowing instead of raining. You can't arbitrarily change one variable, and leave everything else the same. It would be more direct and accurate to simply say that if a cold front from the NNW preceded our developing wave, we would all have a shot at snow. But it looks like the atmosphere will swirl in a different direction.

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earthlight

earthlight

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I usually agree with you, and I rely on your posts for lots of info, but I don't like this explanation. I can't remember any storm where there was much wiggle room for the NYC metro. We don't live in a good location for snow. We're relatively far NW, yet still right along the ocean. When the NAO is negative, we often get suppression. When the PNA is positive, sometimes a trof amplifies too fast and strong and a storm cuts inland. The marine influence doesn't help with any kind of low level southeasterly flow. When both indices are favorable and the EPO and AO are also negative, sometimes a mid-level southerly flow sets up and we get ice. Other times the baroclinicity is weak and/or there is no triggering shortwave/PVA.

I don't think the "pattern" is to blame for some of the guidance suggesting a NYC snowstorm and then taking it away. I'm very much against the generalized characterization of atmospheric flow into numbers. I think it's best left as a tool for climatologists. The pattern doesn't dictate the weather. Rather, the weather - the movement of air in the atmosphere - determines how we characterize the pattern. When you watch your breath on a cold morning as you exhale, sometimes it swirls one way, sometimes another. It's chaotic motion - random and unpredictable. Snowstorms are hard to come by around here. We've had warm weather since October and one major snowstorm just west of the metro. Now it looks like another near miss. That's way better than average for this time of year. I think it's lazy to say that if the NAO was negative we'd get a snowstorm. That's kind of like saying if it were colder it would be snowing instead of raining. You can't arbitrarily change one variable, and leave everything else the same. It would be more direct and accurate to simply say that if a cold front from the NNW preceded our developing wave, we would all have a shot at snow. But it looks like the atmosphere will swirl in a different direction.

Good post. The point I was trying to make was that there was less wiggle room that usual. I agree that it takes a ton of stuff to get a snowstorm here. The pattern has to be just right. But typically, when you have some sort of blocking...maybe a well positioned ridge out west.. a neutral to negative AO...or basically anything better than what we have now..it makes it just a slight bit easier for some of the puzzle pieces to fall in place.

The way it is right now, the fine line we usually walk to get a snowstorm becomes even finer. Without any winter-like antecedent cold, the storm system doesn't have much to work with to start. Then, you factor in the lack of blocking. This means that the storm can either a) come just a hair too far west and give us all rain, b ) take the literally perfect track and timing and give us rain and then some snow, or c) scrape us with rain showers or go out to sea.

In a better pattern, with more favorable teleconnections/upper air setup...these shifts would not be so detrimental to our snow. Sure, the immediate coast would still probably be pissed as a track like this often brings cold air. But if we had more blocking/etc...the pattern would be better all around. There would be more cold air..and the blocking would only allow the storm to come so far northwest by means of physical limits.

Basically the point I was trying to make is that blocking and a more supportive pattern makes things easier. Getting a snowstorm here is always hard. But the pattern we are in def. makes it harder.

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TheTrials

TheTrials

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I usually agree with you, and I rely on your posts for lots of info, but I don't like this explanation. I can't remember any storm where there was much wiggle room for the NYC metro. We don't live in a good location for snow. We're relatively far NW, yet still right along the ocean. When the NAO is negative, we often get suppression. When the PNA is positive, sometimes a trof amplifies too fast and strong and a storm cuts inland. The marine influence doesn't help with any kind of low level southeasterly flow. When both indices are favorable and the EPO and AO are also negative, sometimes a mid-level southerly flow sets up and we get ice. Other times the baroclinicity is weak and/or there is no triggering shortwave/PVA.

I don't think the "pattern" is to blame for some of the guidance suggesting a NYC snowstorm and then taking it away. I'm very much against the generalized characterization of atmospheric flow into numbers. I think it's best left as a tool for climatologists. The pattern doesn't dictate the weather. Rather, the weather - the movement of air in the atmosphere - determines how we characterize the pattern. When you watch your breath on a cold morning as you exhale, sometimes it swirls one way, sometimes another. It's chaotic motion - random and unpredictable. Snowstorms are hard to come by around here. We've had warm weather since October and one major snowstorm just west of the metro. Now it looks like another near miss. That's way better than average for this time of year. I think it's lazy to say that if the NAO was negative we'd get a snowstorm. That's kind of like saying if it were colder it would be snowing instead of raining. You can't arbitrarily change one variable, and leave everything else the same. It would be more direct and accurate to simply say that if a cold front from the NNW preceded our developing wave, we would all have a shot at snow. But it looks like the atmosphere will swirl in a different direction.

We get suppression around here when the NAO is east based and or its positioned in a way to trap a PV too far to the south, like 2009-2010. Time and time again the best storms have a west based -NAO, often a david straits block, and without that block we would be screwed.

Give me a properly placed -NAO or davis strait block over any other pattern, because without it, you get tomorrows craptastic storm. No way you can just say when the NAO is negative, we often get supression, that is just a blantant generalization that is probably not true.

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snywx

snywx

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yea. even though we're about the same latitude, im too far east or closer to the coast than you are. this is really an extreme NW NJ to NW CT stripe snowfall. my soundings suck:

http://68.226.77.253...FC/NAM_KDxr.txt

Yeah.. The further east you are with this situation the longer its gonna take to flip to snow. Like you said.. from NW NJ up towards the Litchfield Hills in NWCT and into the Berks should see mostly snow from this ( especially elevations 1000' and higher)..

Take a 30 min ride north on rt. 8 from 84.. Im sure you will run into some good snows..

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eduggs

eduggs

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I think I may rain for 1 or 2 hours at the onset but the bulk of the precip here should fall as snow. Im becoming more confident in a 6"+ storm for my immediate area..

To me it looks like about 1.2 liquid, changing to parachute bombs around 05z with .8 additional frozen on the GFS. The NAM looks to start the snow bomb an hour or two earlier - maybe .3 liquid followed by 1.1 frozen. Just rough estimates for Middletown. This still has snow bomb potential from Reading to Allentown to Port Jervis to New Paltz, especially above 600feet. Maybe even 20 miles SE of there. Once 925mb to 800mb cools, with large UVV, you could get parachutes to the ground. The problem with our stronger wave is the low level warmth, but we might also get better precip intensity and dynamic cooling. The hilltops NW of the line I described are in line to get in excess of a foot if modeling holds course. Possibly the biggest storm of this early season.

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eduggs

eduggs

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Good post. The point I was trying to make was that there was less wiggle room that usual. I agree that it takes a ton of stuff to get a snowstorm here. The pattern has to be just right. But typically, when you have some sort of blocking...maybe a well positioned ridge out west.. a neutral to negative AO...or basically anything better than what we have now..it makes it just a slight bit easier for some of the puzzle pieces to fall in place.

The way it is right now, the fine line we usually walk to get a snowstorm becomes even finer. Without any winter-like antecedent cold, the storm system doesn't have much to work with to start. Then, you factor in the lack of blocking. This means that the storm can either a) come just a hair too far west and give us all rain, b ) take the literally perfect track and timing and give us rain and then some snow, or c) scrape us with rain showers or go out to sea.

In a better pattern, with more favorable teleconnections/upper air setup...these shifts would not be so detrimental to our snow. Sure, the immediate coast would still probably be pissed as a track like this often brings cold air. But if we had more blocking/etc...the pattern would be better all around. There would be more cold air..and the blocking would only allow the storm to come so far northwest by means of physical limits.

Basically the point I was trying to make is that blocking and a more supportive pattern makes things easier. Getting a snowstorm here is always hard. But the pattern we are in def. makes it harder.

We basically agree, maybe 2/3rds agreement. But not on some of the specifics like the utility of blocking.

In the cliffs notes version I use for my simple brain, you need cold and you need wet. They seem never to go together. Usually it's cold and dry or warm and wet - and for good reason. If you want cold you want a strong block, -AO, -NAO, -EPO. If you want wet (storm) you want +PNA, high amplitude trof, high baroclinicity, strong vort etc... To me these factors counterbalance each other. They are not ingredients in a cake. So we are always walking a tight rope. Pull too hard one way and it's cold and dry. Pull too hard the other and you get a huge storm but rain.

In Dec, Jan, and early Feb I root for stormy and wet and hope that the time of year figures out a way to cool the boundary layer. In the late winter and spring I root for cold and figure the time of year will figure out a way to manufacture moisture. I usually assume that it's non sensical to root for both because they are competing forces. Strong blocks are correlated to major snowstorms in the Mid-Atlantic and the Southeast, but less so for New England and NNY. They are also even more strongly correlated to dry weather and a suppressed storm track.

If the PNA is consistently positive and you have a high amplitude global jet stream, eventually things will buckle in a way that allows cold and storm to meet in our region. Often this can be described statistically as a -NAO regime, or a trending NAO.

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psv88

psv88

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We basically agree, maybe 2/3rds agreement. But not on some of the specifics like the utility of blocking.

In the cliffs notes version I use for my simple brain, you need cold and you need wet. They seem never to go together. Usually it's cold and dry or warm and wet - and for good reason. If you want cold you want a strong block, -AO, -NAO, -EPO. If you want wet (storm) you want +PNA, high amplitude trof, high baroclinicity, strong vort etc... To me these factors counterbalance each other. They are not ingredients in a cake. So we are always walking a tight rope. Pull too hard one way and it's cold and dry. Pull too hard the other and you get a huge storm but rain.

In Dec, Jan, and early Feb I root for stormy and wet and hope that the time of year figures out a way to cool the boundary layer. In the late winter and spring I root for cold and figure the time of year will figure out a way to manufacture moisture. I usually assume that it's non sensical to root for both because they are competing forces. Strong blocks are correlated to major snowstorms in the Mid-Atlantic and the Southeast, but less so for New England and NNY. They are also even more strongly correlated to dry weather and a suppressed storm track.

If the PNA is consistently positive and you have a high amplitude global jet stream, eventually things will buckle in a way that allows cold and storm to meet in our region. Often this can be described statistically as a -NAO regime, or a trending NAO.

Awesome explanation for those who speak normal english. I appreciate when things are broken down like this.

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bmc10

bmc10

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We basically agree, maybe 2/3rds agreement. But not on some of the specifics like the utility of blocking.

In the cliffs notes version I use for my simple brain, you need cold and you need wet. They seem never to go together. Usually it's cold and dry or warm and wet - and for good reason. If you want cold you want a strong block, -AO, -NAO, -EPO. If you want wet (storm) you want +PNA, high amplitude trof, high baroclinicity, strong vort etc... To me these factors counterbalance each other. They are not ingredients in a cake. So we are always walking a tight rope. Pull too hard one way and it's cold and dry. Pull too hard the other and you get a huge storm but rain.

In Dec, Jan, and early Feb I root for stormy and wet and hope that the time of year figures out a way to cool the boundary layer. In the late winter and spring I root for cold and figure the time of year will figure out a way to manufacture moisture. I usually assume that it's non sensical to root for both because they are competing forces. Strong blocks are correlated to major snowstorms in the Mid-Atlantic and the Southeast, but less so for New England and NNY. They are also even more strongly correlated to dry weather and a suppressed storm track.

If the PNA is consistently positive and you have a high amplitude global jet stream, eventually things will buckle in a way that allows cold and storm to meet in our region. Often this can be described statistically as a -NAO regime, or a trending NAO.

I like your description and thought process. I would have to agree with your thinking and I think it is for this reason that we often do best when we are in a transitioning phase. For instance, if the NAO state is changing, this speaks volumes about our chances for a storm. It is not often that with a strong value in either direction that the result is beneficial for our area.

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