Plain-language summary:
After it being unseasonably mild for
most of March so far, it will be much colder for all of this week after today. A
short period of rain today will end and turn to scattered snow showers tonight but
mostly occurring Monday into Monday night, mostly along and northwest of the
Appalachians. After a cold but dry Tuesday, an Alberta clipper will bring widespread
snow showers and possibly squalls later Wednesday into Wednesday night, though
total accumulations will be light for most. It will get even colder but stay
dry and sunny for Thursday and Friday. There may be some snow next
weekend, but there is high uncertainty with a lot of model disagreement, with a big storm being relatively unlikely. After perhaps
temporarily turning cold again right afterward, it likely turns milder again later
the following week.
Meteorological discussion:
After it being unseasonably mild for
most of March so far, except last weekend’s snowstorm, an upper-level trough/closed
upper-level low will deepen over the eastern U.S. and Canada today into
tomorrow, bringing colder air straight from the northwest. This is brought on
by a ridge finally building in western North America (positive PNA). This cold air mass wasn’t
particularly cold to begin with, and will modify over the bare ground over almost
our entire region, with almost all of last weekend’s snow having already melted
with this past week’s mild weather. A surface and upper-level low passing to
the north over Quebec is bringing a band of rain showers this morning across southeastern Quebec and eastern New England, except snow over higher elevations (especially the Laurentians) and
northern Maine, as the cold air hasn’t really arrived yet. The steady
precipitation, falling as snow, will be north of the surface low pressure track
and therefore north of our region. By late tonight, as the low pressure moves
to the east, snow will continue over the Laurentians north of the St. Lawrence
River, with a few scattered snow showers elsewhere, mainly over higher terrain.
Given that the storm is moisture-starved with no connection to Gulf of Mexico
or Atlantic moisture, total precipitation amounts will be relatively light in
most places. With the March sun angle and areas of clearing allowing for
daytime heating, scattered snow showers could turn to rain showers in lower
elevations on Monday, but the daytime-induced instability could also make the
showers more widespread given the cold temperatures aloft. With cooling on
Monday night, any rain showers will turn to snow showers, with most of the snow
focusing on the northwestern slopes of the Adirondack, Green, and White
Mountains due to upslope, but with light snow accumulations extending into the
eastern Champlain and St. Lawrence valleys. Areas southeast of the Appalachians
will likely receive little or no precipitation after this morning due to downsloping.
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| Source: TropicalTidbits |
By Tuesday, the cold air will have
been entrenched, with most higher-elevation areas not
getting above freezing, though it will be dry. Meanwhile, an Alberta clipper will
already be in northern Ontario, diving southeastward in the northwesterly flow
brought on by the strong western North American ridge. Given its trajectory, it
will not pick up moisture from the Gulf of Mexico or western Atlantic. However, it will pick up a bit of moisture from the Great Lakes, and given the deep cold air mass, any precipitation will fall as snow, likely a dry
snow with a high snow-to-liquid ratio, perhaps except lower-elevation areas during daytime when surface temperatures will sneak above freezing for a time. With a strong upper-level trough associated
with clipper overhead by later Wednesday into Wednesday night, any daytime
heating with clear spots on Wednesday will lead to instability, setting off
intermittent snow showers and perhaps even snow squalls. These are difficult to
predict more than a day or two in advance, but it is likely that almost all of
our region will experience at least a few snow showers with a light
accumulation, with several inches possible in areas that get nailed by several snow squalls and also in the favored higher terrain spots,
especially along western facing slopes.
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