A winter storm is set to
impact southern New England Saturday into Sunday as a quick hitting system is
set to bring accumulating and plow-able snowfall to the entire region. We
have been closely monitoring this potential over the course of the past several
days and as we draw closer to the weekend, the details being presented to us
have become much clearer and we have a better idea of what to expect.
Meteorological
Insight
Below
are images of the 500mb pattern (images on the left) and sea-level pressure
(images on the right) from today's 12z runs of the GFS and the Euro. For
the 500mb level pattern there are 2 highlighted areas. The 1st
highlighted area is the southern stream energy which will spawn the area of low
pressure which will produce our storm. The 2nd highlighted area is the
northern piece of energy. Initially we were watching as some model
guidance did suggest that the possibility was there for these two systems to
phase with each other, or in other words, combine. In this type of
solution we would be looking at a more power and potent storm system and a bit
slower moving system. However, it's now begging to appear that these two
pieces of energy will not phase (at least over our area) so the southern stream
energy will remain the dominant feature.
The
image on the right, as mentioned above, is showing sea level pressure are there
are two highlighted features here, with the exception of the Euro as the Euro
has yet to develop our surface low yet. The main feature here is the area
of high pressure which is circled just to the north of New England. This
Arctic High pressure is expected to slightly strengthen this weekend and this
will really help to keep colder air in the lower levels of the atmosphere and
at the surface locked in place for a longer period of time and this colder air
will also really help to make for fluffier snow, especially the further north
you go.
Below we fast forward the
GFS/Euro models to 72 hours out, with each projecting how the atmosphere will
look come 7:00 AM EST Sunday. What we can see is both models show a low
pressure track very close to the coast and with that Arctic High Pressure
eventually departing off to the northeast, this will eventually allow for some
warmer air to work in towards the surface and aloft in the atmosphere.
This will be associated with a warm front which will work close to parts
of the region.
As the area of low pressure
develops and strengthens, this will allow for moisture to increase across the
region and with a very cold thermal profile throughout the atmosphere, this
will lead to some excellent snowgrowth and pretty high snowfall ratios, perhaps
as high as 15:1 to 17:1.
What
to Expect
This
is not going to be a classic snowstorm by any means. This isn't a storm
forming from the phasing of two energies, as described above, and the
mid-levels of the atmosphere aren't presenting us with that look which makes us
go...WOW. While light snows may being falling as early as early Saturday
afternoon with snows lingering into perhaps late Sunday morning, the bulk of
the heaviest snowfall is actually only expected to occur in a 4-6 hour window,
likely from late Saturday evening into the overnight hours. This is where
much of the snowfall accumulations will occur. The burst of the heaviest
snowfall will be associated with the nose of the increasing warm-air advection
aloft and a swath of very strong atmospheric lift. During this 4-6 hour
window, we could see snowfall rates potentially exceed 2''/HR. As the Arctic high does begin to depart, allowing for some warmer air to work in, this
will decrease snowfall ratios some and also may allow a changeover or a mix of
sleet and perhaps some freezing rain, especially for portions of CT/RI/far SE
MA. Towards the end of the event though, all areas may experience some
brief periods of sleet as well. Below is current thinking of what to
expect for snowfall totals.
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