FOUS11 KWBC 291927
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
227 PM EST Sun Dec 29 2024

Valid 00Z Mon Dec 30 2024 - 00Z Thu Jan 02 2025

...Northern Lower Michigan...
Day 1...

Storm system in the East will lift northward into Quebec tonight,
grazing eastern Lower Michigan as it heads toward Georgian Bay.
Colder air will wrap in behind the system on the west side,
changing rain to snow tonight starting at the higher elevations
(away from the lake shores) then ending Monday morning. 12Z CAM
guidance ticked up again for amounts, and a few inches are quite
likely over the northern Mitten. WPC probabilities for at least 4
inches of snow are generally <50% around Gaylord though some more
aggressive models do show some areas >6".


...The West...
Days 1-2...

Upper trough and jet will push ashore the West tonight and well
inland by tomorrow, lowering snow levels as QPF lessens. Jet will
flatten across the Great Basin but still provide broad lift on the
poleward exit region from NV/ID eastward to the Rockies. Snow
levels ahead of the front (4000-8000ft) will drop to 2000-6000ft
from north to south by tomorrow, allowing some accumulation at
lower elevations. Onshore flow off the Pacific into western WA/OR
will maintain lighter snow even as heights rise but then fall again
ahead of another (weaker) system tomorrow afternoon/evening. Much
of the snow will diminish by late Monday into Tuesday except for
over northwestern MT (Glacier NP) where additional vorticity will
push through.

For the next two days, WPC probabilities of at least 12 inches of
additional snow are high (>70%) over the higher Cascade regions in
WA/OR as well as across northern ID/northwestern MT and also
through the Tetons into the Uintas (UT) and Park Range (CO) and
into southern central WY. These probabilities lie above
~5000-6000ft to the north and 8000-9000ft or so to the south.


Pacific Northwest... Day 3...

Quasi-zonal flow below a Gulf of Alaska low will carry weaker
height falls into the PacNW coast Tuesday night with light to
moderate precip for the region into the northern Great Basin. Snow
levels are forecast to be between 2000-3000ft from north to south
across the Cascades the cold front splits off near its triple point
and skips inland. WPC probabilities for at least 6 inches of snow
are >50% above about 3000-4000ft in the WA/OR Cascades.


...North-Central Plains...
Days 1-2...

Strong trough that pushes over the Pacific Northwest today rides a
150kt zonal jet over the CO Rockies early Monday while high
pressure builds south from the lee of the Canadian Rockies.
Convergence between this high and lee cyclogenesis over KS will
support an expanding area of precipitation over eastern MT and
northeast WY tonight where it is cold enough for snow and then
across western SD through central Neb Monday where temperatures
become increasingly marginal. A general QPF swath of a quarter to a
half inch can be expected through this path, and local
enhancements from terrain (like the Black Hills) and mesoscale
banding will result in locally heavy snow. 12Z CAMS have increased
just a bit overall, and hint at potentially higher amounts than a
few inches (90th percentile >6"). WPC probabilities for at least 4
inches of snow are high (>70%) across the Black Hills, near 50%
across much of central SD and into the Pine Ridge in NE, and 10-40%
southward into northern/northeastern NE. Lower snow totals are
expected farther east with milder temperatures into Iowa.


...Northeast...
Day 3...

The low tracking over KS/MO on Monday shifts east to the Mid-
Atlantic through Tuesday before shifting up the Northeastern
Seaboard Tuesday night. It's a progressive system, but with the
surface low translating to the coast around Long Island then
strengthening as it tracks northeastward, there is a threat for
banding on the back side of the low as colder air is pulled in from
Canada. Marginal thermals should be overcome at higher elevations
over the Adirondacks and Green/White Mountains esp >1500ft. To the
west, colder air will rush in behind the system across the still
mild Great Lakes and support some lake-enhanced/effect snow
downwind of Erie/Ontario on NW flow Wednesday thru the end of this
forecast 00Z Thu. Sufficient moisture will also be present over the
central Appalachians (eastern WV into the Laurel Highlands) for
some upslope snow. WPC probabilities for at least 4 inches of snow
are moderate (30-60%) there on the west side of the system as it
retreats to Canada. Over New England, higher probabilities ~50-70%
exist over parts of the higher elevations >2500ft in the
Adirondacks, along the northern spine of the Green Mountains, and
into the White Mountains in NH into northwestern Maine where banded
snow is more likely as the low scoots across the Gulf of Maine
into eastern Maine Wednesday afternoon. Additional accumulation is
likely after 00Z Thu.


Fracasso/Jackson


$$

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