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Weekend Disco/Obs Thread


stormtracker

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Are we talking about the 12 to 15 hr time period on the 12z GFS? Also, I don't think we get norluns down here?

you can get them anywhere they're just not very common around here. it's not a norlun.

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Are we talking about the 12 to 15 hr time period on the 12z GFS? Also, I don't think we get norluns down here?

I dont think they are common, but as far as i know it is just an inverted trough that is oriented west to east....usually they are associated with instability but that may just be the standard one that forms off the coast in SNE

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you can get them anywhere they're just not very common around here. it's not a norlun.

Ian is right, it's not correct to call it a norlun (its missing a few of the necessary features), so i stand corrected, its a surface trough which is enhancing convergence

Edit: (for reference)

Five criteria must be met to be considered a NORLUN trough. They are:

  • T1-T5 (approx. 500 feet AGL to 7000 feet AGL [~950 mb to 800 mb for the east coast]) temperature difference is 10C or greater (Basically states that there has to be instability in the low levels of the atmosphere)
  • Boundary layer RH must be greater than 50% with a wind component from off the ocean on one side of the trough (Basically states that you need a decent amount of boundary layer moisture; the wind from the ocean just helps to maintain this moisture)
  • 500 mb positive vorticity advection is observed with associated 700 mb vertical velocity values (This enhances upward vertical motion and increases the depth of the unstable layer)
  • trough axis is expected to be nearly stationary for at least 6 hours.
  • 850 mb flow is very weak or is parallel to the surface trough (Allows snow squalls to continually traverse the same areas)

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