Plain-language summary:
A mostly quiet week is expected, with seasonably chilly not
but particularly cold temperatures. However, it will be rather cloudy with snow
showers from Tuesday to Thursday, especially northwest of the Appalachians.
After a drier Friday and Saturday, a slowly-approaching storm from the west
could transition to a Nor’easter for Sunday and the following Monday, but that is
uncertain and it is too early for any details. It likely turns quite cold for
March for the following week, with the potential for frequent snow showers and
squalls, or even a true coastal Nor’easter.
Meteorological discussion:
Behind the snowstorm yesterday, it is mostly quiet today,
with a mix of sun and clouds for most except some mountain snow showers. It
will be seasonably chilly today and tomorrow, but with no true arctic chill. A
system heading into the northern Great Lakes will weaken and actually dive to
our south Monday night, a symptom of the Greenland blocking pattern combined
with a nearly stalled upper-level low over Atlantic Canada. The upper-level low
will be too broad and far away to give us heavy precipitation, but Atlantic
moisture wrapping around its northern and then western side, combined with a couple
of shortwaves, will produce periods of light snow from Tuesday to Thursday, also
a symptom of the Greenland blocking. The most snow will fall over the
Laurentians, where the warm advection from the northeast is the strongest, and
the northwestern slopes of the Appalachians, where there will be upslope
enhancement. The flow will be somewhat blocked due to the warm advection above
the cold low-level air, leading to the enhanced snow backing into the eastern
Champlain and St. Lawrence valleys. The most widespread snow will occur Tuesday
into Tuesday night. Areas near and just northwest of summits (especially the
Green and White Mountains) could get 8-16” (20-40 cm) this week, with other
areas receiving much less.
As the upper-level low slowly moves to the east after
Thursday, high pressure will settle to the northwest, leading to continued
northerly flow and cold advection, though again there is no arctic chill to
bring down. Daytime high temperatures will still be above freezing in most
lower elevations if there is any sunshine, given the March sun angle. A storm
will be slowly approaching from the west this weekend and could spawn secondary
coastal cyclogenesis and turn into a Nor’easter by next Sunday or the following
Monday. The slow movement is due to the blocking pattern. Such blocking
patterns can be great for coastal snowstorms, but like has been the case for
the entire winter, this does not appear conducive for a true big Nor’easter due
to the ever present -PNA forcing the trough to dive into the western U.S.
initially and then mature in the Plains and Midwest U.S. before shearing out
over the persistent Gulf of Mexico ridge. Like almost every storm since late
February, it would probably weaken as it heads southeastward before possibly
re-strengthening along the East Coast. With the Greenland blocking, very strong
western Atlantic trough, and not much of a northern disturbance to give it an
additional boost, it could just slowly slide off to the southeast and slowly
strengthen, preventing heavy precipitation across most of the northeast U.S. However,
if the system is a little stronger with a weaker western Atlantic trough, heavy
snow would encompass more of New England, and a lot can change in a week.
After that potential storm, more Bering Sea ridging and for
once, a bit of a western U.S. ridge, will send more arctic air into the U.S.
for the following week. While it will be modified by the March sun angle, and
it will not be record cold, it could feel more like January or February, with
any shortwaves producing short periods of light to moderate snow or even snow
squalls. The upper-level pattern also might be more conducive for true coastal Nor’easter
development and coastal snowstorms, but given how far out it is, ensembles only
show a very vague signal for now, and it is getting more difficult, though
certainly not impossible, to get snowstorms in southern and coastal areas.
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