Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
327 PM EDT Tue Apr 15 2025

Valid 00Z Wed Apr 16 2025 - 00Z Sat Apr 19 2025


...Interior Northeast...
Days 1-2...

Upper low across Ontario will slowly pivot east-northeastward
through the course of the D1 time frame leading to height falls
across much of the interior Northeast. At the surface, a cold front
is analyzed from the VT/NH border down through the Mid Atlantic
with an accompanying CAA regime occurring in wake of the front.
Coldest air that will help contribute to a switch from liquid to
frozen dominant precip is still situated back across the Central
Great Lakes, but the forecast is generally on track for the CAA
pattern to lead to a changeover from rain to snow within the next
3-6 hours. 850mb temperatures will drop to -6 to -8C over the
interior with surface temperatures in the upper 20s to low 30s
overnight, supporting snowfall over the higher elevations and even
some snow into many lower elevations from western/central NY to the
North Country west of the Hudson Valley. The strong CAA will help
promote lake-effect snow to areas south of Buffalo and into the Tug
Hill Plateau as lake temperatures are near 3-6C. Snow will have a
harder time accumulating this afternoon due to the initial warmth,
but overnight most accumulation will occur across NYS. Into
Wednesday, westerly flow will promote upslope enhanced snow into
the Adirondacks and northern Green/White Mountains as well as
northwestern Maine, where some favored ski areas (esp VT) may see
over a foot of snow. Snowfall will end Wednesday evening through
early Thursday from west to east as heights begin to build back
through the Great Lakes into the Northeast. WPC probabilities for
at least 4 inches of snow are >50% over the higher elevations
within the Chautauqua Ridge, over the Tug Hill/Adirondacks, and
into northern VT/NH. Probabilities for at least 8 inches are
highest over northern VT (>50%) encompassing Jay Peak.


...Northern/Central Rockies...
Days 2-3...

There has been little change in the forecast synoptic pattern that
will yield some impressive snowfall totals in-of the Northern and
Central Rockies into the Inter-Mountain west. Strong height falls
plunging southward out of southwestern Canada Wednesday morning
will drive a cold front through Montana and Wyoming, setting up a
period of wintry weather through Thursday (north) and Friday
(south). Northeasterly flow post-FROPA will provide plenty of
upslope enhancement into northwestern MT Wednesday amid ample lift
in the column and lowering snow levels. Moderate to perhaps heavy
snow is likely along the Lewis and Flathead Ranges (HREF probs for
>1"/hr rates are around 50-80%) which will see the highest snowfall
totals. Snow will expand southward late Wed into Thu through WY as
snow levels crash from over 8000ft to below 3500ft (reaching the
valley floors). Lighter snow will extend eastward into the western
High Plains beneath a split upper jet and also west of the Divide
with less upslope/moisture. By later Thu into early Friday, the
cold front will move into northern CO with snow expanding into the
central Rockies as well as across UT which will feel some affect
from the incoming SoCal upper low.

WPC probabilities for at least 8 total inches of snow during the
D2-3 period are high (>70%) over much of the higher terrain of
western MT and especially northern WY mountains, including areas
extending from the Lewis Range to the Absarokas and Bighorns
(mostly above 6000-7000 ft). Much of the Wind River Range has
probabilities >70% for at least 8 inches of snow and many of these
ranges have at least moderate (40-70%) chances of a foot of snow or
more. Significant totals >6" are increasingly likely across the
Central Rockies within CO with the highest probabilities (>70%)
located within the Laramie Mtns for D3 bleeding into what would be
D4. A secondary maxima is forecast within the southern UT
mountains, especially over the Tushar Mtns. where the combination
of favored upper ascent due to the ULL to the southwest will
interact with a digging shortwave out of the Northern Rockies
creating a stronger height anomaly across the Great Basin leading
to heavy snow prospects over the final 24 hrs of the forecast
cycle. The favored trend has led to probabilities for >8" to
increase to 50-70% across the above area with >70% over elevations
greater than 8500ft.


...Central Sierra...
Days 2-3...

There has been no change to the previous forecast as our upper low
currently analyzed off the SoCal coast will continue meandering
eastward over the course of the forecast cycle creating a
marginally favorable environment for moderate snow totals over the
Central Sierra's. As the upper low encroaches, light to
occasionally moderate precip will initiate over the terrain given
the prevailing southwesterlies providing upslope ascent. Snow
levels remain quite high (>8000ft) Wed and only fall slightly on
Thu (7500-8000ft) with slightly more QPF by later on day 3 (Thurs
evening/overnight). WPC probabilities for at least 8 inches of snow
through 00z Saturday Friday are low (10-30%) in the high central
Sierra above 10,000ft lending credence to only minor impacts
overall, in agreement with the latest WSSI.



The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Fracasso/Kleebauer