760
FOUS11 KWBC 310915
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
415 AM EST Fri Jan 31 2025

Valid 12Z Fri Jan 31 2025 - 12Z Mon Feb 03 2025

...Northeast...
Days 1 & 3...

Mid-level low pressure over OK early this morning will shift ENE
over the Midwest today and continue to direct broad and strong
moisture advection to the east. A few pockets of freezing rain are
likely over northern PA and Upstate NY on the leading edge of the
warm air advection through this evening with a few hundredths of an
inch possible. Meanwhile, the northern edge of the precip shield
will feature snow bands east from Buffalo across the Adirondacks,
Green, and White Mountains, along with southern NH and far southern
Maine where Day 1 snow probabilities for >4" are around 20%,
perhaps 40% for the higher terrain. Uncertainty has reigned with
the banding potential, but the consensus has agreed on moderate
banding at best starting later this afternoon with max potential
around 6" despite the w-e orientation of the bands in the direction
of motion. Snow tapers off by sunrise Saturday.

The next shortwave trough is currently well off the PacNW Coast,
but rides a strong jet over the Great Lakes on Sunday and the
Northeast Sunday evening. This allows a warm front to lift over the
Northeast with a fairly quick hitting round of snow. Day 3 snow
probabilities for >4" are currently 20 to 40% for only the Tug
Hill, Presidential Range of the Whites in NH and southern Maine.


...Upper Great Lakes...
Day 2...

A fast moving upper level shortwave trough tracking across the
Northern Plains Saturday night will coincide with the diffluent
left- exit region of a 250mb jet streak to provide modest ascent
over the Upper Midwest with an eastward surface low track over
northern MN Saturday night. The warm front ahead of the low lifts
north Saturday evening, increasing 850-700mb WAA to provide
additional low- level ascent and periods of snow from northern MN
on east across the Upper Midwest Saturday afternoon/evening.
Northern WI and the southern MI Upper Peninsula see moderate snow
with locally enhanced lift on the North Shore of Lake Superior on
southeast-to- easterly flow. Light snow spreads over much of MI
early Sunday while the heavier snowfall over northern MN/northern
WI tapers off by Sunday afternoon. WPC snow probabilities for >4"
are 20-50% over northern WI/western U.P. and the MN Arrowhead with
60% probabilities for >6" along the North Shore escarpment.


...Pacific and Interior Northwest/Great Basin...
Days 1-3...

An active and prolonged wintry pattern for much of the Pacific
Northwest/Interior West/Great Basin is expected through midweek. Mild
temperatures in an atmospheric river (AR) will limit heavier snow
to the higher mountain locations with Cascades snow levels around
5000ft through this evening. Colder air under a trough axis and an
approaching cold-core upper low drifting down the BC coast will
become entrenched over the Northwest as precip rates decrease to
light to moderate Snow levels drop to sea level over western WA and
possibly northwest OR on Saturday where they remain through midweek.
The AR will remain focused into northern CA Saturday through
Tuesday with high snow levels (8000ft and up) on the south side of
a strong baroclinic zone.

For D1, strong IVT (>90th percentile over much of the region
today) and WAA will drive heavy precip and multiple feet of snow
above pass level in the Cascades. Day 1 Probabilities for >8" are
50-80% for the Bitterroots and Sawtooths,  and 40-60% for the High
Sierra Nevada and western WY ranges.

Starting tonight colder air will filter in (in typical fashion)
then rush in with a vengeance by Sunday as the upper low over
coastal BC sinks closer to the region. Though QPF will be lighter
overall over WA/OR as the moisture plume focuses into
NorCal/northern Sierra, SLRs will rise and snow levels will fall,
bringing accumulating and impactful snow well below pass level by
Saturday afternoon then into the lowlands/Seattle and possibly
Portland metro by Saturday night. For areas north of CA/NV,
continued onshore flow ahead of the upper low will lead to less QPF
each day but more snow coverage from the cold.

Days 2 and 3 snow probabilities for >8" are focused over
OR/northern CA east across the north-central Rockies with the
heaviest snow continuing over the Sawtooths, Absarokas/Wind River
south through the Wasatch and higher ridges of northern Nevada.


Jackson


$$