Update #2 on weekend storm potential

As of Tuesday afternoon the consensus is still in place for at least some sort of impact to portions of southern New England this weekend from a rather potent coastal storm.  However, the situation is still not clear at all as to what we can expect in terms of snowfall totals.  Some pieces of guidance suggests some areas could see some significant snowfall accumulations (>8-12'') while other pieces of guidance are more moderate (~4-8'').  Given the time frame we are in it is not uncommon at all to have these questions regarding the significance of any impacts. Besides the potential significance of impacts it is also unclear as to the exact timing of everything.  In yesterday's piece we looked at several ensemble members of the American GFS forecast model, we will do the same today.  Below is from today's 12z run of the GFS:

Looking at these individual members which is valid for early Saturday afternoon, we can see continued consensus for some sort of impact.

As we continue to go through the next few days the main area of focus will be on a rather strong piece of energy which is just entering the Pacific Northwest will slide southeastward through the southern Plains into the southeast then swing northward through the Carolina's and off the New England coast.  The image below is also from today's 12z run of the GFS and is looking at 500mb vorticity valid for very early AM Friday morning:

As this energy then begins the northward turn towards the Carolina's and continues moving north this is what we will really have to pay attention to because how this energy and the storm evolve will ultimately determine the impacts we receive.

Looking at today's run for overnight Saturday we notice that the GFS is suggesting the system will "close off" at 500mb well to the south of New England.  Typically when a system is closed off at 500mb, or begins to close off, this is a tell tale sign that the system is at maximum intensity and will shortly begin to weaken.  This process leads to occlusion which essentially shuts off the moisture inflow to the system:

Something else to notice is also how far south the GFS closes off the system at 500mb.  If this would occur then the majority of the heaviest of the snows would remain well to the south of New England with the highest amounts across the mid-Atlantic to NJ.  For us to receive the maximum amounts we would want that to close off just south of Long Island,  The tracks and path of the 700mb and 850mb lows will also be critical because the heaviest banding of snow occurs just to the north and west of these tracks.  Some other computer models, including the European model (which I can't post graphics) also are fairly similar with the 500m depiction and where the system closes off.    

As we go through the next few days we will pay extremely close attention to how the computer forecast models handle the 500mb level and how the pieces of above evolve.  While confidence is high on some sort of impact, confidence remains rather low as to how extreme these impacts will be.  By late Thursday afternoon we should have a much more clear idea of what kind of impacts we are looking at.