Thoughts on Weekend Storm

I have chosen to avoid the hype for the potential major winter storm this weekend.  Now is the time to add some general thoughts.  I am leaning towards a modest snowstorm in Southern New England with the jackpot well to our south.  Our friends in the DMV have been thirsty for a blockbuster snowstorm and it looks like they will get it. 

General Overview
The energy associated with this storm has not yet entered the US.  When it does tonight expect the weather guidance to really lock onto a solution.  As it stands there is pretty remarkable agreement that something will happen along the east coast.  Lets track the upper air energy
06z GFS 500 mb vort valid 10 am Tuesday (image NCEP)
I've drawn the general track of the upper level energy.   It is likely I have drawn it a bit far to the north. It will strengthen as it gets into Dixie and will pick up Gulf and Atlantic moisture.  At the surface the "storm" is not much to look at as of right now.  But by Thursday a weak surface low should be moving across Texas
WPC surface forecast Thursday 7 AM
Fast forward 24 hours and we see a building Western ridge and a deepening eastern trough.  On Friday the original surface low will begin to reform near the Atlantic coast as the system runs up against the Appalachians.
06z GFS 500 mb vort Friday 8 am (image NCEP)
 See the surface chart at the same time and notice the banana high in the Midwest extending into Ontario.  This locks the cold air in pace and gives most places on the cold side of the storm all snow.
WPC surface forecast Friday 7 AM
At this point its time to watch how the upper air evolves.  The American GFS which I have been using to show upper air diverges from the European (which I can't show $$) in small but significant ways.  The 500 mb low closes off further north on the GFS allowing for more moisture into Southern New England.  The EURO closes off further south the northward extent of the moisture is much less.  The low feeds off a 300 mb jet max which is further south and east on the EURO.  I tend to agree with the EURO because that high pressure in Ontario will slide into Quebec/Northern New England.
WPC surface forecast Saturday 7 AM
So up to this point I have high confidence in a major storm for the Mid Atlantic- a true mauler.  The high pressure is in a pretty sweet spot for SNE- though I would like it just a bit further north.  That high will limit how far north the storm can come and will in turn force it out.  Now that usually is a good thing but this storm may not make the 40/70 benchmark which is the sweetspot for Southern New England storms.  This scenario means the Southern New England coast will take a battering.  With a full moon Saturday tides will already be high.  Add in this storm and there is potential for moderate-major coastal flooding. 
WPC 5 day precipitation totals through Sunday 7 AM
This chart shows the sharp cut off with moisture.  The ski resorts will not do well with this storm.  Here is my snow potential.  I will work on wind/coastal impacts later this week but the threat looks to be substantial in SE MA.
Snow threat guess- Zack Green

Today I will watch the upper air trends and surface tracks and try to narrow this down more.  Please do not go crazy and cancel plans.  The storm is 120 hours out.  Friday and Friday night look fine for our region.  Saturday afternoon looks to be the target start time but experience tells me this will fluctuate.  Twitter/facebook for questions

-Zack Green


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