Plain-language summary:
A week-long or longer sub-freezing
stretch has begun today, though it will not be exceptionally cold. Lake-effect
snow will affect northwestern New York to southern Quebec today, with snow
showers and squalls elsewhere. It will be drier tomorrow except very near Lake
Ontario, with a widespread light snow event occurring later Tuesday into
Tuesday night, with a slightly bigger snowstorm possible for Maine. After a couple
of chilly but mostly dry days Wednesday and Thursday, except a little
lake-effect snow just east or northeast of Lake Ontario, a snowstorm is
possible later Friday into Saturday, but this is very uncertain and is more
likely in southern coastal areas. It then dries out with the coldest air of the
winter so far next weekend, but then becoming much milder and staying dry for
at least the first half of the following week, before colder air and snow
possibly return afterward.
Meteorological discussion:
After the departure of yesterday’s
Great Lakes cutter storm, it has turned colder, and sub-freezing temperatures
will be persisting for over a week for the first time this so far very mild winter.
Although a very cold arctic air mass has descended into the Plains, the
trajectory of the cold air mass heads first into the Plains and then eastward across
the Great Lakes before reaching our region, which means that the cold air mass has modified
substantially, and surface temperatures are actually still slightly above
average for now. However, very cold air aloft, along with a shortwave mid-level
trough, is inducing a heavy lake-effect snow band off Lake Ontario, streaming all
the way into southern Quebec in the deep southwesterly flow. Elsewhere, the mid-level
trough is inducing scattered snow showers and even squalls, with the most
accumulation over higher terrain, but with most areas getting at least a
dusting of snow, perhaps except parts of the Champlain Valley due to downsloping.
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| Source: Aviation Weather Center |
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| Source: TropicalTidbits |
It will be chilly but not unseasonably
cold on Monday, with it being drier behind the shortwave trough but still with
deep westerly to southwesterly flow due to the vertically stacked and
slow-moving low pressure over northwestern Quebec. The exception will be just
east or northeast of Lake Ontario, where lighter lake-effect snow will continue.
At the same time, another shortwave trough will rotate around the vertically
stacked low pressure, inducing a weak low pressure to form over the Southeast U.S. by Monday night. The low pressure will then move offshore and
strengthen, but a little too late for a big snowstorm except possibly for
Maine. For the rest of the region, lighter snows are expected, with less the
farther west you go. It’s a missed opportunity for a big snowstorm, since the upper-level
trough position is in a very favorable position for one if the system was initially stronger.
There’s still some uncertainty on exactly how strong the storm gets and how far
northwest the heavier snow gets, and some last minute forecast adjustments are
expected.
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| Source: TropicalTidbits |
After that, deep southwesterly flow continues
due to the vertically stacked low pressure lingering over northern Ontario, albeit weaker than today. Aside
from areas just east or northeast of Lake Ontario, Wednesday and Thursday will
be dry. Another disturbance will enter the Rockies and the Plains on Thursday,
and could interact with the lingering piece of the polar vortex over northern
Ontario on Friday to produce a snowstorm across the mid-Atlantic and northeast
U.S. Friday night into Saturday. My hunch is that it will initially be weak and
moisture-starved until it is near the mid-Atlantic U.S. coast, and then it
could strengthen and bring in Atlantic moisture. However, there is flat zonal
flow rather than a ridge to the east, which means that the storm would probably
slip eastward instead of pulling northward, so the snow might miss us to our
south. However, there is still much uncertainty on this, and there is a small
chance of a bigger widespread snowstorm for our region if more of the
upper-level low can energize the system, cause it to strengthen quicker, and
back the flow more to allow more Atlantic moisture to be advected into our region
and the storm to come farther north.
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