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

Valid 12Z Tue Apr 15 2025 - 12Z Fri Apr 18 2025


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

Upper low along the Ontario/Quebec border this morning will
continue eastward into the Gulf of St. Lawrence by tomorrow
morning, with a surface cold front moving offshore the Northeast
today. That will bring in colder air to the region and a changeover
from rain to snow. 850mb temperatures will drop to -6 to -8C over
the interior with surface temperatures in the upper 20s to low 30s,
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 areas south of Buffalo,
over the Tug Hill/Adirondacks, and into northern VT/NH.
Probabilities for at least 8 inches are highest over northern VT
(>50%).


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

Strong height falls plunging southward out of southwestern Canada
late Wed 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 30-60%) 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 inches of snow during this period are
high (>70%) over much of the 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. Lower probabilities exist over
UT/CO for at least 6 inches of snow through 12Z Fri but more snow
is to come there into Saturday.


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

A slow-moving upper low west of California today will finally move
into SoCal on Thursday, with some downstream generally light
precipitation into the Sierra Wed/Thu. Snow levels will be 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 12Z Friday are
low (10-30%) in the high central Sierra above 10,000ft.



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


Fracasso