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Big Snow threat, what will it do, part II


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Sometimes a side topic comes up and people want to finish a debate/point on something. As long as it doesn't go on past a page I don't see the big deal.

Do we really want model threads again? It may work if we keep it to just 0z, 6z, 12z, and 18z all inclusive model threads, but we don't need 18z DGEX and 6z NMM WRF threads clogging the forum.

Yes!  I'd like to see that.  It would be more organized and users could get information more quickly and efficiently.  We should try it with 12z today?

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What is the sig of the 280 K surface?

 

Well to put it very simply, 280K is 280 Kelvin first of all. And to make it very simply, that is showing a forecasted projection of how this parcel would travel starting at the location of where the 280K isentrope would be found. Basically  it's showing you how this would traverse upwards . Notice how if you follow the product..you see it moving from 850-800-750mb..etc as it moves north and then northeast.  It's a complicated product, but that is a very simplistic view for those that might not understand. 

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This n of pike overrunning snows better pan out and not fizzle in next 24 hrs of modeling or this threat goes from good to long shot .

 

 

I certainly wouldn't be banking on overrunning being the primary reason to get widespread 12"+ on that map.

 

I'd be going something like low end warning if I had to guess right now.

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Well to put it very simply, 280K is 280 Kelvin first of all. And to make it very simply, that is showing a forecasted projection of how this parcel would travel starting at the location of where the 280K isentrope would be found. Basically it's showing you how this would traverse upwards . Notice how if you follow the product..you see it moving from 850-800-750mb..etc as it moves north and then northeast. It's a complicated product, but that is a very simplistic view for those that might not understand.

It is fascinating to me that a met can pull a map like that up when needed. Is it an in house NWS product that can deliver that?

Sorry for the OT

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I certainly wouldn't be banking on overrunning being the primary reason to get widespread 12"+ on that map.

I'd be going something like low end warning if I had to guess right now.

I could see someone right on the coast (Cape Ann? NH seacoast) getting 10-12" with fronto, but nothing like that depiction
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GFS would bring the WAA snows up...first surface low develops off the Carolinas but largely misses...then we wait for whatever else the atmosphere can stir up.  I know that absolutely this isn't the same exact situation again, but it seems like we've had this happen a couple of times with these first systems robbing the best upper support that comes later.

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Thanks, Chris.

 

No problem. The isentropic charts are just a good way of viewing WAA processes. Isentropes  (which the 280 K surface is) slope up towards the cold side. So a parcel being forced towards the cold air will glide up the surface (because lift is usually an adiabatic process it won't leave the 280 K surface). The faster it moves through pressure levels the stronger the lift, more potential precip, etc. The GFS for example brings parcels from around 900 mb on the south coast to near 750 mb by the time they reach PWM. That's pretty strong WAA lift.

 

Of course this blows up a little when there are diabatic processes like latent heat release going on (then parcels will leave their isentropes). But it's a good way of looking at the atmosphere in 3D rather than being tied to looking at only lift at one level.

 

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No problem. The isentropic charts are just a good way of viewing WAA processes. Isentropes  (which the 280 K surface is) slope up towards the cold side. So a parcel being forced towards the cold air will glide up the surface (because lift is usually an adiabatic process it won't leave the 280 K surface). The faster it moves through pressure levels the stronger the lift, more potential precip, etc. The GFS for example brings parcels from around 900 mb on the south coast to near 750 mb by the time they reach PWM. That's pretty strong WAA lift.

 

Of course this blows up a little when there are diabatic processes like latent heat release going on (then parcels will leave their isentropes). But it's a good way of looking at the atmosphere in 3D rather than being tied to looking at only lift at one level.

 

will be nice when AWIPS II is released from unidata and the poor non-nws folks can get a hold it

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It is fascinating to me that a met can pull a map like that up when needed. Is it an in house NWS product that can deliver that?

Sorry for the OT

 

We have the option to do isentropic analysis with most of the models (Euro included). These maps I have are special procedures I have built so I can use one click to pull it up. But I think Ryan has posted similar NCEP produced maps for the GFS before.

 

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No problem. The isentropic charts are just a good way of viewing WAA processes. Isentropes  (which the 280 K surface is) slope up towards the cold side. So a parcel being forced towards the cold air will glide up the surface (because lift is usually an adiabatic process it won't leave the 280 K surface). The faster it moves through pressure levels the stronger the lift, more potential precip, etc. The GFS for example brings parcels from around 900 mb on the south coast to near 750 mb by the time they reach PWM. That's pretty strong WAA lift.

 

Of course this blows up a little when there are diabatic processes like latent heat release going on (then parcels will leave their isentropes). But it's a good way of looking at the atmosphere in 3D rather than being tied to looking at only lift at one level.

 

 

It's not an easy process to explain to someone for sure. I try to tell people to treat it as an equal density surface where it would travel following this line of equal density. That obviously governed by adiabatic processes. Unsaturated or saturated.

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