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FOUS11 KWBC 100809
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
409 AM EDT Thu Apr 10 2025

Valid 12Z Thu Apr 10 2025 - 12Z Sun Apr 13 2025


...Great Lakes & Interior Northeast...
Days 1...

Light snow is expected this morning across portions of north
central PA into southwest NY. Marginal temperatures support mostly
rain by mid morning, but before then areas could see a coating to
inch of accumulation. As the system moves slowly east do expect
more coverage of light snow by tonight as temperatures cool over
eastern NY into New England. Guidance has trended a bit cooler,
and so anticipate the ptype to become mainly snow or a rain snow
mix overnight, with the exception of coastal areas which will most
likely stay rain. Most areas will pick up a coating to inch of
snow, although probabilities of exceeding 2" have increased over
the Berkshires, southern Green Mountains, Catskills and southern
Adirondacks, with a 40-60% of amounts locally exceeding 2".


...New York into New England... Day 2 and 3...

A large scale trough and developing closed low will bring another
round of precipitation to the Mid-Atlantic and Northeast Friday
into Saturday. More uncertainty with the details of this system,
with notable spread in the 00z guidance. The general trend has
been a further south and east track of the developing low, likely
making this a colder system. However temperatures will still be
marginal, and any axis of notable accumulating snowfall will
probably be rather narrow on the northern periphery of the
precipitation axis. The 00z GFS is the most aggressive solution,
bringing ample precipitation into the colder airmass resulting in
a more significant snowfall solution from eastern NY into northern
New England. On the other end of the model spectrum some solutions
have trended far enough south and east to result in a suppressed
enough solution that little to no precipitation falls in the form
of snow. The most likely scenario is in between this more
suppressed solution and snowier GFS solution.

The expectation is that precipitation lifting north into the
colder air will be snow by later Friday night into Saturday
morning. While some mix with snow is possible in lower elevations,
the best chance of accumulating snow will be in areas of
terrain...with the Catskills, Berkshires, Green Mountains and the
Worcester Hills into the White Mountains the most favored areas.
The probabilities of 2" have increased over these areas, generally
in the 50-80% range, with 4" probabilities over 40% on a localized
basis. A solution in between the 00z GFS and ECMWF (closer to the
ECMWF) best aligns with this axis of higher probabilities...with
the 00z AIFS also well aligned with the current WPC forecast. The
00z ECMWF being a bit further south brings more accumulating
snowfall into the Poconos of northeast PA into portions of
northwest NJ. While this is a lower probability outcome it can not
be ruled out, thus some chance amounts over these areas see some
upward adjustment in future forecasts.


...Cascades to Northern Rockies...
Day 1-3..

Periods of light to moderate snow area expected over the Cascades
today through saturday, with snow levels lowering with time. Some
accumulating snowfall is likely as low as around 2,000 feet, with
total snowfall over 6" expected in the more favored terrain areas.

A strong mid level shortwave moving across the Northwest will
bring a snow threat to the Northern Rockies by Saturday into
Saturday night. Southerly flow ahead of this shortwave will result
in a warm system initially, with most snow falling above 6,000
feet. However behind the shortwave temperatures will rapidly drop,
resulting in lowering snow levels and bringing the threat of some
accumulating snowfall to more of central MT. More uncertainty with
this lower elevation snowfall as model differences in the low
track and strength will impact the amount of precipitation on the
cold side of the system. So the greater confidence for
accumulating snowfall remains over the higher terrain over 6,000
feet, with probabilities of exceeding 6" through 12z Sun as high as
50-80% over the Little Belt Mountains and the Lewis and Swan
Ranges of northwest MT.

Chenard

$$