BOX
System passing through region today will intensity rapidly over
Maritimes over next few days. This becomes critical to the track
of the winter storm since it affects flow downstream from us,
mainly by helping strengthen confluent flow aloft which in turn
prevents ridging from helping to slow down and maintain
strength of upper trough. This should result in opening up of
500 mb low, which is shown by just about all models with
exception of 00z NAM which is an outlier and does not fit this
expectation.
Upstream, we also do not see much upper level ridging across
northern Rockies which would be needed to help deepen trough
over eastern states. This also allows system to open up as it
passes our region instead of closing off or maintaining its
strength.
What all this means is there is less of a chance that coastal
low comes much closer to coast than 40/70 and it won`t have a
chance to deepen rapidly as it passes our area, thus limiting
impacts such as widespread heavy snow and strong winds. In
addition, models show strongest 850 wind field and moisture
convergence across NJ and Long Island before both weaken with
time as they reach SNE.
All of these factors argue against a "blockbuster storm" for the
entire region but there are other considerations that certainly
favor heavy snow including presence of deep southern stream
moisture and a cold airmass in place which should yield high
snow to water ratios (fluffy snow). There is likely to be a
tight snowfall gradient somewhere in northern MA (thinking Route
2 right now) but this could shift north or even south in future
model runs. It does look like best chance for seeing 6-12" of
snow is along and south of the Mass Pike with 2-6" north of
there, but again, this may shift in later forecasts. Then
there`s the issue of low level temperatures which may cause
p-type issues or prevent accumulations on the outer Cape and
Nantucket.