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FOUS11 KWBC 280808
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
308 AM EST Fri Feb 28 2025

Valid 12Z Fri Feb 28 2025 - 12Z Mon Mar 03 2025


...Upper Great Lakes through the Northeast...
Days 1-2...

An unusually strong clipper system (MSLP below the first
climatological percentile per the ECMWF) diving southeast from
southern Canada will head for the Upper Great Lakes this morning.
The storm will reside beneath the diffluent left-exit region of a
90-100 knot 500mb jet streak, while also sporting an unusually
strong NWrly IVT that surpasses 300 kg/m/s on the western flank of
the surface low. The low-level circulation at 850mb is also rather
potent with heights that are below the 0.5 climatological
percentile by 18Z Friday according to NAEFS. This equates to what
is effectively a "front-end thump" of heavy snow that began
overnight in the Minnesota Arrowhead and is now heading for the
Michigan U.P. and far northern Michigan today where the best 850mb
FGEN occurs. The 00Z HREF suggests snowfall rates of 1-2"/hr are
possible for several hours this morning. A dry slot and warming
boundary layer should limit snowfall over the Michigan U.P. and
northern Michigan Friday afternoon, resulting in a narrow swath of
heavy snow. As the storm heads east though, additional snow is
likely on the back side of the storm as low-level cold-air
advection (CAA) over Lake Superior increases Friday evening. Snow
should taper off by Saturday morning in the Upper Great Lakes. WPC
probabilities show moderate-to-high chances (50-70%) for snowfall
totals >6" in the MN Arrowhead with similar chances for >8" in the
Keweenaw Peninsula, Huron Mountains, and eastern Michigan U.P..
Localized amounts approaching a foot are possible closer to Sault
Ste. Marie, MI and neighboring communities to the south along the
coast.

The storm continues its march east into southern Ontario Friday
evening with the same method of producing periods of heavy snow as
far east as the Tug Hill and Adirondacks of northern New York.
WPC`s Snowband Probability Tracker, utilizing the 12Z HREF
guidance, shows the potential for 1"/hr rates from the Tug Hill to
as far east as the Green and White Mountains Friday night. Unlike
the Upper Great Lakes, however, the storm track is farther north
through the St. Lawrence Valley. This burst of heavy snow will
eventually give way to diminishing snowfall rates late Friday night
and into Saturday morning in these areas. By Saturday morning,
only northern Maine likely to still see periods of moderate-to-
heavy snow through rest of the day Saturday. However, as the
Arctic front approaches midday Saturday, steepening lapse rates
and strong upper-level ascent aloft is a recipe for snow squalls.
Plummeting temperatures could result in quick accumulations on some
surfaces, but the biggest concern is for dramatic reductions in
visibilities within impacted areas of northern New York and as far
east as northern New England Saturday afternoon. Travelers on
roadways should be sure to have a reliable way to receive snow
squall warnings should they be issued on Saturday. Snow should
gradually taper off throughout the Interior Northeast by Saturday
evening, with some lake-effect showers lingering into Sunday. WPC
probabilities show moderate-to-high chances (50-70%) for snowfall
>6" in the Tug Hill and Adirondacks neighboring the Tug Hill
through Saturday morning. Similar probabilities for >4" of snowfall
are depicted across northern Maine, as well as the Green and White
Mountains through Sunday morning. Localized amounts topping 8" are
possible in the tallest peaks of the Green and White Mountains.


...California & Great Basin...
Day 3...

A closed upper-low approaching California on Sunday will direct an
IVT that is topping out not much higher than 250 kg/m/s at the
Sierra Nevada and Southern California ranges. 850mb and 700mb winds
topping the 90th climatological percentile (per NAEFS) may aid in
some modest upslope flow, but this IVT is not particularly strong,
which should limit most heavy amounts to the highest/more remote
elevations. Snow levels will be as low as 4,000ft from the Sierra
Nevada on east into the Great Basin, but the heavier amounts will
generally be confined to elevations above 6,000ft. Snow will fall
heaviest over the Sierra Nevada and as far north as the
Shasta/Siskiyou Sunday afternoon and into Sunday night. As the
upper low approaches Sunday night, Pacific moisture will spill over
into the Great Basin with moderate-to-heavy snowfall along the
ridge lines of central Nevada Sunday night and into Monday. WPC
probabilities depict moderate-to-high chance probabilities (50-70%)
for snowfall >8" at elevations above 7,000ft in the Sierra Nevada
through Monday morning. Similar moderate-to-high chance
probabilities for >4" of snowfall exist along the ridges of
central Nevada through Monday morning.


Mullinax



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