The second significant snowstorm of the winter season for Southern New England (third if you include October) looks to, like its predecessor, deliver heaviest snow to extreme Southeastern Massachusetts and Cape Cod.  A progressive storm system (moving quickly) ensures greatest precipitation amounts in Eastern New England, with a sizeable drop in amounts the farther west and northwest one is.  Perhaps the biggest question is whether we actually cool the atmosphere sufficiently for snow - coming off high temperatures near 50 in some of Southern New England on Friday, it will take time for the air to cool.  As a result, precipitation will start as rain along the South Coast and Cape Cod overnight Friday night, changing to snow Saturday morning.  At this point, given the likelihood of a northerly wind and available cold air in Northern New England, I'm expecting the change to snow to occur between 7 and 9 AM, even on most of the Cape from west to east.  This should leave most of New England in a shield of snow with temperatures at or just barely above freezing.  Of course, this leaves me a bit nervous, as a matter of just one or two more degrees will make for rain, not snow, in many areas.  Nonetheless, this is the best estimation I have of how the storm will unfold.  As such, greatest snow amounts will be found where the air is sufficiently cold for snow, and the maximum axis of precipitation falls, which is likely to be the Western end of Cape Cod, and just west/north of the Cape Cod Canal.

Southern New England:

Northern New England:

In a winter that's on-pace to provide one of the least snowy winters on record for the Boston area and much of Southern New England, any chance of significant snow gets folks excited, anxious or curious.  As such, I'm receiving lots of questions about Saturday's snow potential.

In Wednesday night's weathercast on NECN, we looked at the players involved: an arctic front marking the leading edge of a strong surge of cold air crossing New England Saturday, an energetic disturbance lifting northeast from the center of the country, and an active subtropical feed of moisture and energy available to our south.  If all three of these come together, you get a big storm.  If two come together, you get accumulating snow.  If they all come at you but don't link up, you get snow showers.  At this point, some interaction of at least the northern cold air and Central US energy looks likely on Saturday.  I can also tell you, however, that right now the timing on getting more southern moisture involved is just a little out of sync with the other two disturbances, meaning a big storm remains a low probability at this point.  That said, a small change in timing on the arrival of these disturbances would make a significant storm more likely.

So...here's what I can tell you:

• High confidence that snow will fall
• Moderate confidence that road treatments/plows will be needed in much of New England Saturday
• Low confidence on exact amounts - early estimate map below
• Start time Saturday sunrise, end time around sunset
• Blast of cold air follows for Sunday

Interestingly, the method of precipitation and snowfall estimate that proved so successful from days in advance in several events last winter, is indicating at least six inches for most of the Hartford, Providence, Boston, Worcester, Portsmouth and Portland corridor.  That said, this method is based upon computer guidance precipitation estimates, and though current forecasts are quite moist, I am unwilling to bite on more than 3"-6" given the inability for multiple stream phasing of disturbances to occur in the forecasts.  If I see a trend toward multiple disturbances phasing, I'll be more inclined to believe estimates of as much as 10" in the Boston area.  For now, my best estimate is in this map...highest amounts in Southern/Eastern New England, lowest in Northwestern New England.