Coastal Storm to Bring Accumulating Snowfall to southern New England Tuesday into Wednesday

Confidence in a coastal storm bringing accumulating snowfall continues to increase as computer model guidance over the past few days has come into further agreement on a further northward track.  The time of impact will be from late tomorrow morning/early afternoon lasting into mid to late morning Wednesday with the height of the storm occurring late evening through the overnight period.

Shortwave energy will be entering the United States from the northern Plains during the overnight period, rotating around a piece of the polar vortex which is situated north of Maine in Canada.  As this energy digs into the United States it is expected to strengthen and the response will be for surface low pressure development.

Throughout the day tomorrow this piece of energy is expected to strengthen as it continues digging into and through the Ohio Valley into the mid-Atlantic states and as it does show the energy/trough will become negatively tilted.  This will not only allow for further intensification (cyclogenesis) of the low pressure system but this will help to keep the track close enough to the coast for impacts.  We will also see the system slow down a bit as it passes just off the New England coast.

Late evening tomorrow and through the overnight period, as the system works northward just off the coast, it will undergo rapid cyclogenesis and we will see a rather intense and mature storm system develop.  This is evident as computer forecast models are developing closed off circulations at the 925/850/700mb levels.  When this occurs we will begin to see a very intense band of extremely heavy snowfall develop and where this band traverses is where the highest snowfall totals will occur.  At this time this appears to be across portions of SE CT/RI and into far SE MA which includes the Cape.

What's going to happen is light snows may begin to break out as early as late morning/early afternoon with periods of moderate bursts of snow during this time.  While a few inches may drop during the afternoon hours the heaviest of the snow is expected late evening/overnight.

While we have a rather cold airmass in place which is a positive for higher snowfall ratios, forecast model soundings are also highly suggestive of very favorable snowfall growth and snowfall rates.  This will lead to extremely fluffy snowfall composed of rather big snowflakes.  This will also be a positive for higher snowfall totals.

With an intensifying storm system just off the coast this will lead to a tightened pressure gradient which means increasing winds, especially across eastern MA.  This will lead to blizzard conditions across eastern MA and this can't even be ruled out for areas further west.  Given such an intense system with such strong lift and forcing, some thundersnow is also possible.

At the height of the storm, snowfall rates may approach as much as 2-3'' per hour, especially considering the snow will be so fluffy.  The highest snowfall totals should be confined to eastern southern New England as this is where the consensus is for the higher precipitation totals.

Below is what I'm expecting right now: