There Will Be Snow, Wind. How Much and When?

A good portion of Southern New England will be impacted by a winter storm Wednesday thru Friday.  In the fantasy world of numerical weather prediction (models) the American GFS looks like it has scored a big upset; the EURO has trended towards a major storm in the region which is why I am willing to make the call this morning.  There is still some uncertainty for SNE because the new and improved Canadian is on board for just a few inches of snow.  Let's break it down

Tuesday
Another day with a mix of sun and clouds.  Our old friend the Upper Level Low will slowly pull away but the key word is slowly.  Temperatures to start the morning are largely in the 20's
2 m temperatures 5 am EST (image weatherbell)
Temps will rebound to the low 40's for most, mid 40's in CT
09z RAP 2 m Temp 1 PM EST (image weatherbell)
Winds today will be less than yesterday (6-9 mph) and out of the north.  

Storm Discussion
This is technical- feel free to skip down to the forecast.
HPC surface chart 522 AM EST
A piece of energy from the Southwest and a Low pressure system from Western Canada will merge in the Ohio River Valley, occlude, and spawn a new low pressure center near the NC/VA line.  I've tried to illustrate the process above.  The system already has a lot of moisture
Upper MS Valley NWS regional radar 530 AM  EST
This system will be into Kentucky and spreading its effects North and East by 7 PM tonight
HPC forecast surface chart 7 PM EST
Now there are two scenario's.  First scenario is the large scale forcing takes over and allows the low to come further north as the American GFS shows.  Most likely the main center of the storm stays south of the 40/70 benchmark.  However it is so large and given the block and slow movement of storms in the North Atlantic vicinity there will be interactions bewteen the various systems.  I think the interaction between a low moving into Southern Canada on Thursday will enhance precipitation/snow for New England

Here is the GFS at 500 mb
00z GFS 500 mb vort valid Wednesday 7 PM
Here is the NAM 
00z NAM 500 mb vort valid Wednesday 7 PM
Here is the EURO at 48 and 72
00z EURO 500 mb heights Wed 7 PM (image weatherbell)
See the energy over the UP of Michigan?  
00z EURO 500 mb heights Thu 7 PM (image weatherbell)
That energy is now near Toronto on Thursday.  So that will be the battle.  All of the guidance indicates interactions at 500 mb so I am confident in several inches Thursday into Friday.   The EURO control is in line with the GFS, NAM, GEFS, JMA.  The op EURO is close...so going with a decent slug of snow tomorrow night through Friday.

STORM FORECAST
During the day Wednesday only light precipitation falls.  Any snow will not accumulate as we can expect surface temperatures to be running above freezing.  
00z EURO 2 m Temp max Wed PM (image weatherbell)
The heaviest precipitation begins by midnight south of the MA/RI/CT border.  Winds should begin to crank by then
00z NAM hires 900 mb winds Thursday 1 AM (image weatherbell)
These are over hurricane force just a few thousand feet up.  With the heavy precipitation expected one can expect these to mix to the surface at times, especially over the Cape.  The problem then becomes the stall.  With the block in place this storm will stall offshore.  This will allow precipitation to be heavy enough to accumulate during the day Thursday and will also devastate the eastern facing coast.  The Thursday morning high tide is likely the worst of the bunch.  Here is the total precipitation by Thursday morning
HPC 2 day precipitation totals
If we add a day look how much falls Thursday-Thursday night
HPC 3 day precipitation totals
With the winds sustained at 25-30 mph Thursday
06z NAM 10m winds, mslp Thu 7 am (image weatherbell)
There will be widespread downed trees and powerlines.  The snow will be heavy and wet.  Combine the winds and we are looking at a mess.  I'll post a snow map this afternoon but in general 
06z NAM snow accumulations (image weatherbell)
I think the heavy wet nature of the snow holds totals down.  Some guidance is crazy; it may be right so I want to take a bit more time to look it over.  Have a good day!






















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