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2/4-2/5 Clipper OBS


Capt. Adam

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fwiw, it underperformed big time out here.  Expecting 4-6", ended up with 1-2" on ratios that were way lower than anticipated.  Here's to hoping you guys do better!

 

Thanks for the update.  If I'm reading some of the other sub-forums correctly, seems like maybe a tight cut-off issue vs the precipitation underperforming?  MI reporting good ratios.

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This won't be like the "Cape May Clipper" last week, "surprising the area" with 5-7" of snow (most likely). The equation for that one was faily simple: strong channelized cyclonic vorticity advection / strengthening MPV/frontogen / cold and somewhat unstable profiles. Tonight is more diffuse with different forcings going on in different locations (with a close juxtaposition over our area).

 

Perhaps the Chicago area saw lower amounts than forecasted, but what happened there is actually still impressive for us (being downstream). There was a 2-4" snowfall with 15:1 ratios as quick hitting warm-air advection / lower mpv ahead of the mid level vort max sped through. There is sneaky 700mb / mid level frontogen in our northern zones / southern New England with an increasing moisture gradient/advection. Profiles also are interesting in the northern half (Leigh Valley to C NJ points north) with some instability noted on the soundings. While warm/moist advection may fuel the "higher QPF" in S NJ, the 700mb frontogen is basically absent and snow growth isn't ideal. Either we all see a uniform snowfall in a quick duration tonight or maybe the north will surprise us with a banding feature and see 2-4 inches. Hard to predict amounts like that with the speed of this system and lack of factors coming together to increase the omegas.

 

Looking forward to the new SREF guidance.

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This won't be like the "Cape May Clipper" last week, "surprising the area" with 5-7" of snow (most likely). The equation for that one was faily simple: strong channelized cyclonic vorticity advection / strengthening MPV/frontogen / cold and somewhat unstable profiles. Tonight is more diffuse with different forcings going on in different locations (with a close juxtaposition over our area).

 

Perhaps the Chicago area saw lower amounts than forecasted, but what happened there is actually still impressive for us (being downstream). There was a 2-4" snowfall with 15:1 ratios as quick hitting warm-air advection / lower mpv ahead of the mid level vort max sped through. There is sneaky 700mb / mid level frontogen in our northern zones / southern New England with an increasing moisture gradient/advection. Profiles also are interesting in the northern half (Leigh Valley to C NJ points north) with some instability noted on the soundings. While warm/moist advection may fuel the "higher QPF" in S NJ, the 700mb frontogen is basically absent and snow growth isn't ideal. Either we all see a uniform snowfall in a quick duration tonight or maybe the north will surprise us with a banding feature and see 2-4 inches. Hard to predict amounts like that with the speed of this system and lack of factors coming together to increase the omegas.

 

Looking forward to the new SREF guidance.

question, when you look at a sounding or map what do you look at to show if frontogenesis is present? Do you go off the vertical velocity for the lift?

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question, when you look at a sounding or map what do you look at to show if frontogenesis is present? Do you go off the vertical velocity for the lift?

 

Technically, at the very least, you need isotropes (potential temperature) and wind plotted. Frontogenesis isn't really a stagnant thing so it is a function over time of temp advection. There are plots of frontogenesis made from the SREF, NAM etc. at different pressure levels if you don't have GEMPAK. If you just go off the UVM, you may not know what's causing the lift. On regular weather maps that you use day to day, see if you can make out deformation, converging temperature and if each side of the front is growing cooler or warmer for whatever reasons that usually cause cooling/warming.

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