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4/17-18 snow threat


ORH_wxman
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25 minutes ago, ORH_wxman said:

Wonder why the Kuchie maps are even higher? They should be punishing the amounts for the sfc temps being slightly above freezing. In fact, the Kuchera algorithm starts punishing temps above 28F.

 

Is it because they are just factoring in mid levels and not surface temps? 

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Just now, Allsnow said:

Is it because they are just factoring in mid levels and not surface temps? 

No, the Kuchera formula is actually not that complicated...it takes the max temp in the column between and if it's greater than 271K (basically 28F), the formula is ratio = 12 + 2(271K - Tmax)....so if the max temp is like 33F, you'd have ratio = 12 + 2 (271 - 274) = 12 - 6 = 6...so we should get like a 6 to 1 ratio if a Tmax of 33F....if it's 32F, then maybe like 8 to 1.

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Just now, ORH_wxman said:

No, the Kuchera formula is actually not that complicated...it takes the max temp in the column between and if it's greater than 271K (basically 28F), the formula is ratio = 12 + 2(271K - Tmax)....so if the max temp is like 33F, you'd have ratio = 12 + 2 (271 - 274) = 12 - 6 = 6...so we should get like a 6 to 1 ratio if a Tmax of 33F....if it's 32F, then maybe like 8 to 1.

Gotcha. Thank you for that explanation. 

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1 minute ago, SouthCoastMA said:

Slight tick south on 18z NAM (10miles?)..but still looks a bit north of euro

Yes....subtle south shift. As expected. Too far north at 12z. Looks closer to 06z again albeit more zonked on QPF. Prob not realistic on the widespread 0.75-1.0" QPF in MA/CT/RI,

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4 minutes ago, ORH_wxman said:

Soundings def have a massive crosshair sig on them during the initial thump....there's going to be good snow growth I think.

Good snow growth with 32-34F surface temps can get some fun flakes.... good dendrites going the aggregate route can lead to some good vis reduction too. 

Much more efficient accums on warm ground surfaces than throwing a bunch of melting needles/columns through the low levels.

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9 minutes ago, ORH_wxman said:

Soundings def have a massive crosshair sig on them during the initial thump....there's going to be good snow growth I think.

I noticed that on the NAM and GFS. Nice look for areas that can chill the boundary layer sufficiently. 

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