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klw

NNE Winter 2014-2015 Thread Part 2

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I understand fearing the ratio game, but it looks like we could see a period of 15 or even 20:1 snows I would think in my region.

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we have just been bumped up to a warning for 4-8 now.

Yeah all 12z models get at least a half inch of QPF up to me and you...even up to the Canadian border on the GFS/EURO/NAM.

Assuming 12:1 ratio that's close enough for a warning.

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I will say the isentropic charts show pretty rapid saturation occurring. The field is actually called condensation pressure deficits when looking in an isentropic sense, but generally less than 20 mb deficit is good enough for precip to occur. GFS has no problem achieving this, Euro is a little delayed but not denied, and NAM/CMC would be a little worrisome (but that may just be a grid resolution problem for me).

Great info! Thanks for the run down. I always wonder when it's this cold how much gets eaten up before saturation occurs.

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Great info! Thanks for the run down. I always wonder when it's this cold how much gets eaten up before saturation occurs.

 

Dry air always lurking. It's a blessing and a curse sometimes. It may take a little longer to saturate, but it also doesn't take as much moisture to saturate.

 

I'd be a little more concerned if we had temps in the teens or something, but 7/0 or 5/-2 probably isn't going to murder us.

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Yeah all 12z models get at least a half inch of QPF up to me and you...even up to the Canadian border on the GFS/EURO/NAM.

Assuming 12:1 ratio that's close enough for a warning.

 

Yeah the Euro would suggest a solid foot for both of our locations.

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Here is what I was talking about earlier. You're looking at the 285 K potential temp surface at 12z Monday. Without diabatic processes going (adiabatic) air parcels should maintain their respective potential temperatures, thus 285 K parcels would travel solely on this surface displayed here.

 

So you have southerly winds of 50-55 knots on this surface, which are moving from pressures in the 950s (near the surface) to pressures around 700 mb (mid levels) in a short distance. This is insentropic lift that you'll hear mentioned in AFDs, and it's pretty strong at that. You want to see parcels moving up pressure surfaces (rising) like this not down (sinking).

 

The shading represents the condensation pressure deficit. Essentially this is how much a parcel would need to rise in order to reach the condensation point, so 20 mb (blue and cooler colors) is a small number.

 

post-44-0-36720700-1422819539_thumb.jpeg

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Here is what I was talking about earlier. You're looking at the 285 K potential temp surface at 12z Monday. Without diabatic processes going (adiabatic) air parcels should maintain their respective potential temperatures, thus 285 K parcels would travel solely on this surface displayed here.

So you have southerly winds of 50-55 knots on this surface, which are moving from pressures in the 950s (near the surface) to pressures around 700 mb (mid levels) in a short distance. This is insentropic lift that you'll hear mentioned in AFDs, and it's pretty strong at that. You want to see parcels moving up pressure surfaces (rising) like this not down (sinking).

The shading represents the condensation pressure deficit. Essentially this is how much a parcel would need to rise in order to reach the condensation point, so 20 mb (blue and cooler colors) is a small number.

attachicon.gif285K.jpeg

Thanks for the informative post...we need more content like that! I'll be honest that's close to going over my head but I think I understand it. I would assume raising a parcel 20mb isnt really all that hard to do as that's not much height change in the grand scheme of things.

What would a far distance be? Like 75mb? 150mb?

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Thanks for the informative post...we need more content like that! I'll be honest that's close to going over my head but I think I understand it. I would assume raising a parcel 20mb isnt really all that hard to do as that's not much height change in the grand scheme of things.

What would a far distance be? Like 75mb? 150mb?

 

Yeah it's pretty deep in the weeds kind of stuff, but is basically how WAA precip works. You can have a gradual slope (parcels rising 200 mb from ISP to like Quebec City) or it can be steep slope (parcels rising 200 mb from ISP to RUT like this event). Steeper the slope, the more intense the lift. It's the "why" when we talk about front end thumps.

 

To answer your question about 75 mb condensation pressure deficits are when you would say things are basically too dry to precipitate.

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This is what I was talking about earlier about a west-east band of snow setting up somewhere over NNE.

 

Current radar shows its already developing over the Lakes as expected.  This area should advect into NNE tomorrow mid/late morning.  Fairly favorable mid-level tracks.

 

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Event totals: 1.3” Snow/0.02" L.E.

 

There was a final tenth of an inch from this morning's weak upper level disturbance to finish off the accumulation.

 

Details from the 6:00 P.M. Waterbury observations:

 

New Snow: 0.1 inches

New Liquid: Trace

Temperature: 4.5 F

Sky: Mostly Clear

Snow at the stake: 11.5"

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Started snowing around 5:15 in BTV. Small cold flakes with some blowing. If I can get out today I'll take some scenics.  Should look downright wintry. 

 

Looking at the updated high res models it looks like pretty reasonable consensus that we're looking about .5" qpf over the northern greens. Pretty interested to see how this "stacks" up these cold temps and winds with an easterly component. 

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If we are going to make a run at 7 inches or so we are going to have to see heavier snow than this.

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Started snowing around 5:15 in BTV. Small cold flakes with some blowing. If I can get out today I'll take some scenics.  Should look downright wintry. 

 

Looking at the updated high res models it looks like pretty reasonable consensus that we're looking about .5" qpf over the northern greens. Pretty interested to see how this "stacks" up these cold temps and winds with an easterly component. 

 

Been snowing pretty good here at the mountain, dead calm winds.  Looks like a slightly blocked southeasterly flow which can be good here, but just getting a steady 1/2" per hour since I got here at 5:30am.

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I think we will bust low. It appears we are getting shadowed here with good bands north and south.

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Unless it picks up soon we will underperform here.

 

That is what I was thinking as well. Though looks like it has picked up a little...at least down by the lake and water in the last 30 minutes or so. 

 

Frankly, I think at these temps it's hard for snow to accumulate. Small flakes, no stick. 

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