Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
325 PM EST Wed Feb 14 2024

Valid 00Z Thu Feb 15 2024 - 00Z Sun Feb 18 2024

...Northwest and Intermountain West...
Days 1-2...

A strong shortwave trough moving into NorCal/OR will move into the
coast as a retrograding trough pushes west off the coast of WA.
The merging of these 2 areas of energy will result in a
developing, albeit short-lived, low over WA State through Friday
morning. The low will quickly shear apart and dissipate by Friday
evening. The interaction of these shortwaves and the resulting
upper low will provide plenty of lift over the well-entrenched
Arctic air mass over all of the Intermountain West. Further,
strong onshore flow in the lower levels will advect plentiful
Pacific moisture into the Pacific Northwest as well. The result
will be a long-duration snowfall event, largely highlighting the
Cascades of OR and southern WA, the Boise/Sawtooth of ID,
Bitterroots of MT, the Yellowstone and Tetons, and the Wind River
Ranges of WY. Expect multiple feet of snow over these 2 days in
each of these areas, with maximum accumulations approaching 4 feet
into the OR Cascades which will get the brunt of the Pacific
moisture, and over 3 feet into the Tetons and Wind River Ranges of
WY. Forecast WSSI is for major impacts into these mountain ranges
with Moderate impacts across central ID. Minor impacts are likely
across much of the area from the Cascades east through the High
Plains of south-central MT.


...Great Lakes to the Interior Northeast...
Days 1-2...

Surface low pressure over the central Plains will move ENE tonight
into early Thu toward southern Lower Michigan. In the mid-levels,
a northern and southern stream shortwave will merge/interact over
southern Ontario as the upper jet increases over the Southeast.
Combination of upper divergence and incoming height falls/PVA as
the combined shortwave tries to close off over northern New
England will promote an expanding area of snowfall from the Great
Lakes eastward, initially tied to a modest/strong area of FGEN
over northern Lower Michigan where WPC probabilities for at least
4 inches of snow are greater than 50%. Snow could be heavy in
bands with HREF probs of >1"/hr up to 60-80% around Alpena Thu
morning (and 10-30% probs for >2"/hr). Lower probabilities stretch
back to the west across WI tied to the incoming northern stream
cold front. By D2 (late Thu into Friday), low pressure will slip
steadily eastward through NY into New England before translating
to the Gulf of Maine early Fri. Again, WAA/FGEN into northern NY
and New England will support modest snows with embedded heavier
bands though the quick movement will limit amounts somewhat.
Still, WPC probabilities for at least 4 inches are high (>70%)
over much of the Tug Hill/Adirondack region and into the
Green/White Mountains in VT/NH.


...Central/Northern Rockies & Central/Northern Great Plains...
Days 1-2...

A fast-moving 500mb vorticity maximum moving through the Great
Basin early Thursday will help guide mid/lower-level moisture to
the Rockies and onto the Plains tomorrow afternoon/evening. Though
the pattern is decidedly blocky over northwestern Canada, it is
quite zonal in the mid-latitudes which will help zip this system
along. However, with Canadian high pressure settling into northern
MT, easterly to southeasterly flow in the low levels will help
draw in some Gulf moisture to the central Plains on the cold side
of a wobbly surface boundary east of the terrain. Mountain snows
over parts of eastern WY into CO will continue through D1 into
early D2 along the surface front, at the same time a broad area of
snow expands eastward in conjunction with height falls as a
mid-level trough moves in from the north. Models have mostly
converged toward an axis from around the Black Hills ESE across
southern SD though the ECMWF-led guidance is still generally
lighter than the GFS-led guidance, tied to a swath of favorable
FGEN at the entrance region of the upper jet. WPC probabilities
for at least 4 inches of snow are high (>70%) over parts of
northeastern WY into the Black Hills and into south central SD (in
addition to the northern CO Rockies). Though probabilities for >8"
are low (~10%), 12Z HREF probs of >1"/hr around 20-40% suggest
there could be some embedded higher amounts not fully realized in
the ensemble guidance. The system will continue through the Mid-MS
Valley/Mid-South with a swath of light snow along I-70 into the
Ohio Valley, but probabilities for at least 4" are currently lower
than 10%.


...Central Appalachians/Mid-Atlantic...
Day 3...

The system mentioned above will continue eastward on D3, spreading
light snow from the OH/TN Valley eastward Fri evening into the
central Appalachians beneath a ballooning upper jet (wide expanse
of >150kts from the Mid-South to Bermuda with a jet max
approaching 200kts over VA). Low pressure is expected to move
across eastern TN and continue quickly eastward as height falls
dig into the Great Lakes/Midwest/central Appalachians. QPF will
move through the region into the Mid-Atlantic overnight, which
would help with accumulations assuming the boundary layer can cool
off enough. There will be a transition to cold rain over parts of
southern VA closer to the track of the low, where the NBM ptype
probs maximize uncertainty. However, slight tick colder in some
guidance suggests accumulating snow across much of the region,
focused mostly on eastern WV with help from upslope enhancement.
There, WPC probabilities for at least 4 inches of snow are
moderate (40-60%), with lower probabilities into the Laurel
Highlands and eastward across southern PA. Measurable snow is
likely all the way to the coast/beaches and perhaps as far south
as around the Richmond area (depending on thermals).

Fracasso/Wegman