Saturday Snow Event – Update

I’m still sticking with my call from yesterday afternoon you can see in the previous post. The radar looks good this morning and the models generally held serve last night. The Euro/GFS still have 0.5″-0.75″ while the 6z NAM has higher amounts (though it looks like the 12z NAM backed off significantly).

You can see some convective feedback in the 12z NAM 12 hour forecast. Notice the 2 areas of convection (high precip totals) to the east and south of the main low center off the Mid Atlantic coast. What the model is essentially doing is lowering pressures over the convection it’s developing which leads to a strung out appearance to the low. Notice the isobar wraps around both blobs of convection and the main low itself. Will this happen? Probably not. Unfortunately, it’s impossible to judge what the model would show if this convection wasn’t there or in a different location.

BDL is currently 37/28 with colder/drier air to the north and as the winds shift north some of this air will be advected south. Evaporational cooling along with cold advection in the boundary layer should change rain to snow very quickly (or even at the onset) in the hills and a bit slower in the valleys. No change here in my thinking. I still think BL issues are being overplayed by some TV competitors though the NWS is now pretty close to my thinking.

The issues to watch for today:

  • Where does the surface low form? Does it stay close to the shore near best DCVA or does convection over the Gulf Stream string it out and keep it further east
  • Does the 500mb vort max track closer to SNE than the models show? Every model sort of shunts it out south of us but I think the models may be overdoing that eastward jog thanks to stronger downstream ridging over the Atlantic.
  • How fast does the BL cool as precip begins
  • How fast dry slot between Atlantic moisture and mid level forcing get pinched off. It may be a nailbiter.
  • How quickly the mid level lows close off and develop a nice CCB

All in all I’m pretty pleased how things look this morning. I’ll keep you updated.

Ryan

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