The following discussion is a break down on how I think this storm will evolve and an explanation of snowfall totals for this storm.  Here is the current forecast.

Timing of the storm:  The precipitation will start to expand northward into the Philadelphia and New York City metropolitan areas between 7 AM to 10 AM.  The precipitation will be light and scattered.  Dry air at the surface is expected to produce a bout of virga which is when precipitation falls from the clouds but does not reach the ground.

10 AM to 5 PM: The storm will organize along the North Carolina coast and track over eastern Virginia.  As the storm develops, the precipitation shield is expected to expand.  With temperatures warming above freezing, a rain/snow mix is expected over much of the Philadelphia metropolitan area, central New Jersey, and southern New Jersey.  Meanwhile, light snow will develop for the New York City metropolitan area, northeastern Pennsylvania, the Hudson River Valley, and Connecticut.

5 PM Friday through 5 AM Saturday:  The low pressure system rapidly intensifies over the New Jersey coastal waters and tracks towards the New England coastal waters.  All locations change over to snow with intense snow banding expected along the coast.  The worst conditions are expected in this time period with wind gusts over 40 mph, snow rates potentially reaching 1 to 3 inches per hour, and visibility falling below a mile in some locations.  This time period is when blizzard conditions will be possible from central New Jersey through the New York City metropolitan area into southern New England.

5 AM Saturday through 11 AM Saturday:  Storm exits to the east with snow leaving from west to east in the morning hours.  Clearing skies by 12 PM.

LOCATIONS:

1 to 4:  These locations can expect to change from snow, sleet, rain mix to snow last thus the lower snowfall accumulation totals, which will likely happen late tomorrow evening through early Saturday morning.  The faster the change over, the higher the snowfall amounts in these locations.

3 to 6 Inches (Philadelphia metro): Very tricky forecast.  Basic idea is the following.  First, the Philadelphia metro will be on the boarder of where the mixing will occur with the 850 MB temperatures around freezing.  I expect a mix of snow, sleet and rain through tomorrow morning into the evening hours then a change over to all snow. There after, there appears to be a focus for the best dynamics to the northeast of Philadelphia, which I suspect will lead to sinking air over these locations and thus less snowfall.  The potential for that 6 to 12 inch snowfall does exist but the cut off will be VERY sharp.

3 to 6 inches (Eastern Pennsylvania):  These locations can expect mostly snow, however again the best dynamics will be to the east which again could lead to sinking air and a suppression of snowfall totals.  The further west you are, the more likely you’ll be around 3″ with this storm.

6 to 12 inches with locally higher amounts:  Another difficult forecast here.  For the most part these locations are mostly snow however a mix of sleet and snow is still a threat for the region.  Six inches is the base snowfall amount I think but some location is getting over a foot here.  I didn’t push snowfall totals higher because of uncertainty of exactly where the best mesoscale banding will set up.  These locations are likely to have a wide range of snowfall totals and don’t get me started on the potential for thunder snow in this set up.  The issue here is that in locations where the bands are to your north or south, the snow will become suppressed.  As such, staying put with the forecast and will NOW-Cast the event.

12 to 24 inches with locally higher amounts:  These locations can expect the heaviest snowfall with the potential to go over 2 feet in some locations.  All snow can be expected with the best potential for 2 feet or more as you go southeast and east.

WIND POTENTIAL:  

Along the coast look for sustained winds from the northeast veering to the northwest through the period at 15 to 30 mph with gusts easily over 40 mph.  There is a potential for wind gusts over 60 mph on Friday night into Saturday morning.

Just away from the coast (basically east of the Delaware River), winds will be sustained at 10 to 20 mph with gusts over 40 mph with maximum gusts at 60 mph.

For points west of the Delaware River, look for sustained winds at 5 to 15 mph with gusts at most 40 mph.

COASTAL FLOODING:

The worst coastal flooding will be Friday night through Saturday morning with coastal flooding expected to range from moderate to major.  Tides are expected to be seven to eight feet above normal.

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