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FOUS11 KWBC 072007
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
407 PM EDT Mon Apr 7 2025

Valid 00Z Tue Apr 08 2025 - 00Z Fri Apr 11 2025

...Interior Northeast...
Days 1,2...

A compact low tracking from Lake Huron this afternoon east along
the Canadian border and across Maine through Tuesday afternoon will
cause an area of mostly light snow to fall along its track, as most
locations near the track stay below freezing, favoring mostly snow
as the precipitation type. The initial front is largely over the
Ontario Peninsula (the area bounded between Lakes Huron, Erie, and
Ontario) at the time of this writing. Temperatures with this band
are largely above freezing, so any snow embedded within it is not
sticking, especially to roads. Going into tonight, however, without
solar insulation, it`s likely on the higher elevations of the
Chautauqua Ridge, and eventually Adirondacks and points further
east, snow will begin sticking and have some impacts.

The greatest impact from this low for most areas is likely to be
the potential for flash freezing. As sub-freezing air moves in with
the snow, road/ground temperatures could rapidly drop, resulting in
a thin glaze of ice on some colder surfaces. This of course may
have travel impacts. With the snow itself, in some of the stronger
convective cells, visibility in any snow may drop enough to cause
travel impacts as the winds with the snow and cold front become
gusty. Fortunately, the snow is not expected to become very strong,
as a stronger low along the moisture plume off the Eastern Seaboard
saps a lot of energy from this polar low as they track parallel to
one another.

As far as snow amounts are concerned, impacts from this low will
start tonight, increase through the day Tuesday, then peak Tuesday
evening as the snow rates wane as the parent low moves off to the
east. A few inches of accumulation are possible in the valleys from
the Champlain Valley east to coastal Maine. Meanwhile, locally
much greater impacts from much higher accumulations are expected
from the Tug Hill Plateau of central New York to the west, to the
Adirondacks, the northern Greens and Whites of VT and NH,
respectively, and much of western Maine. Local accumulations on the
highest elevations could approach a foot of new snow by the time
the snow is all said and done.

WPC Probabilities are moderate-to-high (50-70%) across far northern
New Hampshire and much of western Maine for 6 inches or more of
snow. Since the heaviest snow will be falling during the day
further west across northern New York and Vermont, those
percentages are much lower (10-30%) in those mountains. Minor
impacts are expected in these areas, though where snow falls
heavier in any convective snow showers, locally greater impacts are
probable.

...Great Lakes...
Days 1-3...

Extensive lake-effect snow is expected behind the aforementioned
low that is moving through the Great Lakes currently. 850 mb temps
will be falling to the west (cold side) of the low to between -12C
and -18C across all of the Great Lakes tonight. Despite this being
the climatologically unfavored time of year for lake-effect (due to
usual warm air in place over the cold lakes), the air will be cold
enough in this case for all of the lakes to support multiple bands
and cellular lake-effect convection from the U.P. of Michigan,
where lake-effect snow is ongoing presently, to western Michigan
off its namesake lake, and later tonight off the lower lakes
through the Chautauqua Ridge and Tug Hill Plateau. As usual with
lake-effect, the typical impacts such as rapidly reduced
visibilities, snow-covered roads, and blowing snow are likely in
the aforementioned impacted areas. The heaviest lake-effect and
greatest snowfall amounts are expected on the Tug Hill where
amounts approaching 10 inches are possible through Tuesday.

A developing low along a slow-moving warm front extending from the
Arrowhead of Minnesota through southern lower Michigan and
eventually into portions of northern New York may cause additional
areas of snow Wednesday Night into Thursday morning. As is typical
during April, temperatures will be hovering right around freezing,
so precipitation type between snow and rain will be a major
determining factor as to accumulations in any one area. A general
1-3 inches of snow are possible in these areas from the low and
front.


...Northern Rockies and Cascades...
Days 1,2...

A pair of shortwave troughs rotating east along the base of a
longwave trough over the northeast Pacific will direct plumes of
Pacific moisture into the Pacific Northwest through Wednesday. Snow
is expected to remain at higher elevations, especially over the
Olympics and Cascades. Higher elevations such as Mt. Rainier may
see multiple feet of snow through the period due to very persistent
and heavy upslope snow. Accumulations will be extremely elevation
dependent, as many valley locations see mostly rain or snow light
enough to not be able to stick to warm surfaces. Measurable snow
will impact many of the mountain ranges of the Pacific Northwest,
including the Blue, Sawtooth, Bitterroots, Absaroka, Teton, and
Lewis Ranges. Strong ridging building in behind the troughs by
Wednesday and Wednesday night will end any remaining high elevation
snow.


Wegman

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