Damage
Mon night/early Tue morning, rain changes over to snow as
far southeast as the I-95 corridor, in response to strong forcing
for ascent and melting snow in the boundary layer. However, despite
snow falling during the Tue morning commute (I95 & points NW), high
res guidance suggest surface temps still above freezing. Therefore,
accumulations for the Tue morning commute likely confined to the
high terrain. However by late morning and especially the afternoon,
surface temps will cool and snow is expected to accumulate in all
areas, except southeast MA, where temps are expected to remain above
freezing. Therefore the late day Tue commute is expected to have
snow covered roads from I-95 corridor, including Boston to
Providence and points northwest. Snowfall rates of 1+ inches are
possible, along with very strong northeast winds yielding low
visibility. Typically a storm track so close to the coast will yield
a rain/snow line well northwest of I-95. However, in this event,
with rapid height falls (cooling from top down thru the column), the
rain/snow line may collapse right to the surface low! By Tue
evening/night, surface low should be just east of our longitude,
with winds shifting to the NNW, and rain/snow line will crash
southeast thru the Cape and Islands. Thus, accumulating snow
continues Tue night as comma head pivots across the area. Snow
tapers off Wed morning, except possibly continuing across CC as
comma head maybe slow to depart. Given the strong height
falls/increasing mid level lapse rates, would not be surprised to
see isolated TSSN Tue!
Given the above attributes, expanded the winter storm watch farther
southeast into the I-95 corridor of Boston and Providence. High
confidence for 7+ inches across the high terrain of MA, resulted in
watches being converted over the warnings. Snow accumulations always
difficult to forecast in March, given increasing sun angle, warm
ground and low SLR. However for this event, heavy qpf of 2-3" (some
guidance sources 4-5"!) supports dynamical and diabatic cooling
processes, that will support heavy snow threat and help offset the
high sun angle and warm ground. In addition, despite low SLR and
some loss in snowfall potential on the front end as ptype will be
rain, plenty of qpf to work with after the changeover. To come up
with a conservative snow forecast given still beyond 48 hours in
model time, we capped SLR to 10-1 with lower ratios in the coastal
plain, and limited snow accumulations to surface temps 32 or colder.
This still resulted in 12-18" in the high terrain, tapering downward
to 4-7 inches in the Boston to Providence corridor. More
importantly, given this will be a heavy wet snow (transitioning to
higher SLR Tue night), past events have shown the onset for snapping
tree branches is 4+ inches. Thus, power outage risk increases where
our snowfall map is greater than 4 inches.
You are primed for 18 or more man. Get everything prepped and put away silly snow maps. This one is pretty well locked up in terms of amounts for most areas iMo . Beast is enroute for a large portion of SNE
