Mid Atlantic Met Class Thread

[gymengineer]

I hope Ian doesn't mind me posting this here- this is on his website from a couple of years ago: D.C.’s double-digit snowstorms: A history and guide to the patterns that produced them

 

[wxdude64]

4 hours ago, psuhoffman said:

Posting this here so it will also bump this thread...

Wanted to do a post analysis of what went wrong regarding the VA/NC storm this week.

Looking at the setup leading it... we see what is a pretty classic look.  Some ridging over greenland combined with a severely displaced PV providing cold locked into the east.  A potent stj wave entering the west coast.  This is a class look a few days before a lot of our big storms.  There was no way at this point to see from range the subtle discreet issues that would ultimately doom our chances right here.  

By this frame though, the problems are starting to show up.  There is still a lot to like there...again -NAO, 50/50, potent stj wave.  But there are warts now.  The 50/50 is a bit south of ideal but worse there is a potent vort/lobe rotating around it down across the Hudson Bay that is about to dive in across New England and flatten the flow ahead of the STJ system.  That alone might have been something we could recover from but in addition in the upper midwest that northern stream system is diving in out of sync with the STJ wave.  Instead of phasing in its behind and acting as a kicker.  The combination of both those factors are going to be the problem.  

And by this frame it is obvious what has gone wrong.  Despite a perfect western ridge axis, -NAO, 50/50 and a lot of things we look for...the combination of those two problems has acted to flatten the flow, the stj system is washing out instead of amplifying, and the whole trough is becoming elongated and flattened under the NS flow.  There were so many ways for that to work.  Either simply get rid of either that NS vort on top OR the one diving in behind it and we probably would have got enough amplification from the STJ system alone to get into the snow.  Get rid of both and it was probably a HECS here.  Another option would be for the system diving in behind to have been 12 hours faster...and they likely would have phased and that would have worked also.  But those two features literally took the worse possible course of events for us and combined to screw up what was a pretty good setup.  

Agree with this. I was hoping (along with many) that the midwest vort would have caught up earlier. It MAY have robbed me and western areas a bit, but it would have pushed low end warning snows into DC/Balt corridor and east. Once it was apparent that wasn't gonna happen I said I-66 would be a wall.....