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Significant Ocean Storm March 5-7 2013 Discussion Part II


earthlight

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Looks like a convective feedback sort of problem that limits the northwest expansion of the precip shield. I would think it's just the model having trouble with the distribution of vorticity, as a CCB rarely looks like that. I thought this was a nice run, staying the course, again around 1" of QPF for NYC metro. The consensus seems to be around 1" of QPF...again a 4-8" snowstorm for NYC, if not a bit more, and 6-10" for the suburbs. Still possible to go up from there but that's a standard TV forecast. I could even go as low as 3-6" for southern Queens and SE LI. 

There is an odd QPF bomb on this run to our east, which I think messes with the precipitation field to the west of the low. I wonder if it had anything to do with the small vort max that escapes from our storm at 45 hours? That's when the QPF bomb was. 

 

gfs_namer_045_500_vort_ht.gif

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Quite a sharp cutoff to out west, makes me worry that another few ticks southeast and we are on the outside looking in. Still a nice run, but don't like the way that it arrives at it's solution. EURO at 1 will answer many questions, however, I need my sleep, and therefore it will have to wait until the morning. Good luck to all!

-skisheep

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This run goes further east at 500mb because it does NOT bridge the block with the ridging out ahead of our storm, like the NAM did. 

Yet we still wind up with over 1 in qpf so that a blend of Nam/Gfs Euro/Sref would yield on average 1.,25 with 30mph guting to 50 in the CCB at night so a conservative call would be 6-10 in nYC?

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At least its colder, so that's my concern

Yeah it's a lot better for LI and gives the possibility for higher ratios in NYC, maybe 11:1 at night in the CCB. NYC gets a hair more than 1" QPF so we're still talking about a solid snowstorm. I think the GFS track should produce slightly more liquid early on, but didn't because of the convective feedback/QPF bomb, a problem that the GFS used to have frequently but which had supposedly been "fixed." Fixed and the GFS are two words that don't go together so I assume it can still be an issue. 

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Ends up being a nice hit despite starting weird, and I think the precip shield would spread out more instead of having that obscene max in the Delmarva/Northern Virginia with areas getting like 1" QPF in 6 hours. 

It continues to have this double QPF max in VA and E MA, and a shaft zone of sorts in between. I can see that happening as the low could phase and bottom out late for western areas. Overall it seems to develop it later than the NAM does. If we have this shadow zone with lighter precip in between the maxes I could see BL being more of a problem. I would imagine this GFS run is a good bit warmer than the NAM below 850.

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Looks like a convective feedback sort of problem that limits the northwest expansion of the precip shield. I would think it's just the model having trouble with the distribution of vorticity, as a CCB rarely looks like that. I thought this was a nice run, staying the course, again around 1" of QPF for NYC metro. The consensus seems to be around 1" of QPF...again a 4-8" snowstorm for NYC, if not a bit more, and 6-10" for the suburbs. Still possible to go up from there but that's a standard TV forecast. I could even go as low as 3-6" for southern Queens and SE LI. 

 

Convective feedback is what overblew the feb 9th storm's model QPF. What makes you think it'll cut down on precip numbers in this one?

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This run goes further east at 500mb because it does NOT bridge the block with the ridging out ahead of our storm, like the NAM did. 

GFS and NAM while both showing a formidable winter storm event, are worlds apart. NAM is showing a temporarily crippling storm that lasts into Thursday night or early Friday, while GFS for all intensive purposes ends it early Thursday AM. A difference of almost 24 hours, an inch of liquid, and probably 6-10" wet snow. Which idea is right or neither? We still don't know.

WX/PT

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Yeah it's a lot better for LI and gives the possibility for higher ratios in NYC, maybe 11:1 at night in the CCB. NYC gets a hair more than 1" QPF so we're still talking about a solid snowstorm. I think the GFS track should produce slightly more liquid early on, but didn't because of the convective feedback/QPF bomb, a problem that the GFS used to have frequently but which had supposedly been "fixed." Fixed and the GFS are two words that don't go together so I assume it can still be an issue. 

Could be a feedback issue-look at the diamond shaped convective blob that develops from 36-45 hrs out over the Gulf Stream-it kept doing a similar thing prior to the 2/8 storm that sheared the whole system out too much, right up until it formed. Looks in this case like it yet again shears the comma head portion out and weakens it. Highly suspect in my view and something that's plagued the model before.

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Convective feedback is what overblew the feb 9th storm's model QPF. What makes you think it'll cut down on precip numbers in this one?

If I had to take a stab at this, I'd think about the concept of convection... if a model is overdoing convection in one area (strong upward vertical motion), it will also overdo subsequent sinking motion... in this case, if theres a huge QPF bomb in one area, the model is going to try and add subsidence into the areas around it, squashing he precpitation around it...  that QPF bomb would, in reality, probably be spread more evenly rather than in one location...

Does that make any sense mets?

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If I had to take a stab at this, I'd think about the concept of convection... if a model is overdoing convection in one area (strong upward vertical motion), it will also overdo subsequent sinking motion... in this case, if theres a huge QPF bomb in one area, the model is going to try and add subsidence into the areas around it, squashing he precpitation around it... that QPF bomb would, in reality, probably be spread more evenly rather than in one location

it would addittionally mess with the dynamics of the Lp and potentially alter its track on the model as well
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If I had to take a stab at this, I'd think about the concept of convection... if a model is overdoing convection in one area (strong upward vertical motion), it will also overdo subsequent sinking motion... in this case, if theres a huge QPF bomb in one area, the model is going to try and add subsidence into the areas around it, squashing he precpitation around it...  that QPF bomb would, in reality, probably be spread more evenly rather than in one location...

Does that make any sense mets?

If you look at the run, it develops a massive concentrated blob of convection over the Gulf Stream at around hr 36, and notice how much weaker the precip is just north of it. It focuses energy over that blob and essentially robs the rest of the storm of moisture/energy. I highly doubt that centralized area of convection is real, and yes it does take away from the rest of the storm.

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GFS and NAM while both showing a formidable winter storm event, are worlds apart. NAM is showing a temporarily crippling storm that lasts into Thursday night or early Friday, while GFS for all intensive purposes ends it early Thursday AM. A difference of almost 24 hours, an inch of liquid, and probably 6-10" wet snow. Which idea is right or neither? We still don't know.

WX/PT

 

 

Yeah, it really is still unknown. Since the NAM links the NAO block with the ridge out ahead of the storm, it really blocks the storm from drifting eastward, in similar fashion to Sandy's super block.

 

The GFS keeps those two features separate, thus there is more of a weakness for it to escape east. That being said, it's still impressive verbatim. 

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If I had to take a stab at this, I'd think about the concept of convection... if a model is overdoing convection in one area (strong upward vertical motion), it will also overdo subsequent sinking motion... in this case, if theres a huge QPF bomb in one area, the model is going to try and add subsidence into the areas around it, squashing he precpitation around it...  that QPF bomb would, in reality, probably be spread more evenly rather than in one location...

Does that make any sense mets?

 

 

This makes plenty of sense. 

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As Hanibal said to Clarice..."the answers are right in front of you"....itll likely be in the middle of the nam and gfs...srefs say so

I wouldn't be so sure that any models are meeting in the middle. They pretty much reversed, not really trended towards one another. I still think we get 3-6"....not a foot with a blizzard or anything, but not an inch either

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I wouldn't be so sure that any models are meeting in the middle. They pretty much reversed, not really trended towards one another. I still think we get 3-6"....not a foot with a blizzard or anything, but not an inch either

If it's a mix at the start, which I expect, followed by a 7-10 hour period of moderate to heavy wet snow then over, 3-6" would seem about right, yes. But NAM has other ideas with that block.

WX/PT

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I wouldn't be so sure that any models are meeting in the middle. They pretty much reversed, not really trended towards one another. I still think we get 3-6"....not a foot with a blizzard or anything, but not an inch either

 

 

3-6 would be bare bones minimum in a powerhouse Storm like this. For that to happen it would have to Either just Brush us (Skirt off to the South) or be warm and wet for at least of the storm. With over an inch QPF mostly frozen than is more like a 6-12 type storm if you want to be conservative. 

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