Significant/Substantial Coastal Storm to pose significant impacts across southern New England

We are beginning to see some very strong consensus with computer model guidance that a significant/substantial coastal storm will have major/significant impacts across all of southern New England during the day on Friday and continuing through a large part of Saturday.  The impacts will range from snowfall, potential with widespread significant (6-12'' totals) to perhaps substantial (12''+) snowfall accumulations region wide, the possibility of sleet mixing in, especially across the coastal plain, the possibility of thunder/lightning, potential for very strong/damaging winds leading to blizzard conditions and widespread power outages, and coastal flooding/erosion.  All of these hazards and more will be addressed in great detail below.  First off, we will take a look at the meteorology behind the scenes.

-Meteorology behind the storm.

The above image is a 500mb geopotential height/vorticity map from the ECMWF computer model, one of the best and most accurate computer models out there.  This image is from today's 12z (7:00 AM) run and for 48-hours out, meaning this is what is projected for 7:00 AM EST Friday.  I highlighted two areas here as these are the two main features of importance.  In the enclosed blue circles are pieces of energy which are moving through in the mid-level jet stream aloft, roughly 18,000ft ASL.  Energy #1 is looking very strong and intense here and we are beginning to see the energy dig more, allowing for a trough to develop within the jet stream, this is otherwise known as amplification and will allow for this piece of energy to remain strong.  Looking towards energy #2, we notice it is a little more weak in nature as it's working up the coast.  As these pieces of energy continue working through the jet stream flow the northern piece of energy and southern piece of energy will combine, or in meteorological terms we call this phasing.  Once this process occurs we will begin the process of transferring all of it's energy towards the energy moving up the coast, as this process occurs we will begin to see the rapid development of cyclogenesis, or in other words, the development of our coastal storm.  Once this process starts to occur we will be looking at rapid and very intense cyclogenesis.

The above graphic is a chart showing mean sea-level pressure (MSLP) along with 6-HR precipitation from the 12z run of the GFS computer model also for 48-HR out.  I have circled the area with the "H".  This area depicts an area of high pressure and the GFS has the high pressure at about 1036mb which is pretty high.  The GFS, along with several other computer models all show a fairly strong area of high pressure to our north and only drift it eastward very slowly throughout the duration of this storm.  This high is referred to as a "blocking" high and will be of significant importance with this storm as this will make for a very slow moving system, enhancing the impacts we will see.  This area of high pressure along with the rapid deepening of the coastal storm will also play a major significance in the wind potential, as you'll have rapid changes in pressure over a very small distance.

When dealing with the potential for impacts as large as we are looking at the key here will be with regards to the phasing.  As noted above, right now computer models are showing a perfect phase, this means the storm is phasing early enough to where we would see the most significant impacts and the storm will be phasing late enough to where we don't see the storm move inland but stay off the coast keeping the cold air locked in.
Now that we took a little look into the meteorology aspect of things let's take a look at the hazards we may be facing.

Significant/Substantial snowfall accumulations possible:

When using the terms significant/substantial we will define the following as:

Significant - Widespread area of 6-12'' of snowfall with isolated higher amounts
Substantial - Widespread area of at least 12''+ of snowfall with isolated higher amounts

Right now the likelihood of at least 6-12'' of snowfall over just about the entire region is exceptionally high and the potential for a widespread swath of 12''+ is also very high  In fact, the possibility exists for a swatch of snowfall totals ranging from 18-24'' of snow and some isolated higher amounts close to 30'' are certainly possible.  However, right now it's still a little too early to pin down exactly where this will occur.  We could be looking at the potential for snowfall rates to reach 2-3''/HR with even some 4''/HR amounts possible, especially if we see any bands of snow which are associated with thunder.  What also complicates things with regards to where the higher totals will occur is the potential for a dry slot.  With all intense storms they are usually accompanied by a dry slot and to pinpoint if/where the dryslot will occur is a bit difficult right now.  The possibility of mixing will also complicate forecasts a bit, especially closer to the coast.  Snowfall could also be wet in nature, especially for the further south you go leading to heavy wet snow sticking on tree limbs and power lines.

Since this system will be associated with some very potent lift (strong upward vertical motion) along with steepening lapse rates aloft (change of temperature with height) the potential for thunder/lightning will also be possible with this system.  If there is any thunder/lightning that will further enhance snowfall rates locally and this is where 4''/HR snowfall rates are possible.

Several computer models are also showing the potential for some very strong and damaging winds associated with this storm thanks in part to a very strong pressure gradient that will be going over the region thanks to the high pressure to our north and the coastal storm passing just off the coast to our SE.  In fact, some computer models are showing a prolonged period of very intense winds across much of the region and especially the southeast coast.  We could be looking at winds of 25-45 mph sustained with winds gusts as high as 55-65 mph, especially along the coast.  Winds along the coast could even be sustained as high as 45-55 mph.  If future runs don't back off on what we are looking now than wind gusts of 70-80 mph would be possible out across far SE MA along the Cape area. This would lead to blizzard and near whiteout conditions at times and also lead to widespread power outages across the region.

With such an intense coastal storm and strong winds coming in off the ocean this will lead to some major flooding across some of the coastal plane across RI/SE MA and perhaps even across coastal CT.

All in all this is looking like a very dangerous storm.  Snow should begin during the morning hours of Friday with conditions rapidly deteriorating as the afternoon goes on with very hazardous and dangerous travel lasting throughout the night and into the first part of Saturday.  We are looking at the possibility of widespread substantial snowfall accumulations, along with wet snow sticking to limbs/power poles, the possibility of tropical storm to hurricane force winds leading to blizzard conditions and widespread power outages along with major coastal flooding.

Below is a graphic displaying what we could be looking at for snowfall totals.  Keep in mind it is still early so this isn't a fine tuned map and as we get closer and details continue to get resolved the map can be more fined tuned: