Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
346 AM EDT Mon Apr 14 2025

Valid 12Z Mon Apr 14 2025 - 12Z Thu Apr 17 2025


...Western Great Lakes...
Days 1-2...

Vigorous mid-level upper low over the MN Arrowhead this morning
will continue moving eastward across Lake Superior today along with
its attendant surface low pressure. Temperatures in the upper 30s
to low/mid-40s this morning will fall as winds increase from the
north and northwest around the area of low pressure, changing rain
to snow from northern/northeastern MN into northern WI and the U.P.
of Michigan this afternoon and into the evening. After 00Z
tonight, additional mid-level energy will swing around the backside
of the departing upper low, favoring a surge in snowfall into the
northwestern U.P. that may be boosted by some lake-induced steeper
lapse rates (lake temps 4-5C with 850mb temps below -6C). Some
heavier rates of >1"/hr are possible overnight tonight (30-60%
probs from the HREF) which could lead to modest snow totals there
along with gusty winds. Snow will continue across the U.P. into
northern Lower Michigan early Tuesday with additional accumulation.
On Tuesday, snow will end from west to east during the afternoon
into the evening as heights rise from the west. WPC probabilities
for at least 4 inches of snow are highest (>70%) over the U.P. and
moderate (30-60%) over the northern L.P. of MI. In addition,
probabilities for at least 8 inches of snow are >50% over some of
the favored lake areas around the Porcupine and Huron Mountains.


...The Northeast...
Days 2-3...

Canadian low pressure will continue through Quebec as its cold
front brings in colder air to the region. Once the front clears the
coast, another area of low pressure may develop along the
occlusion near northern Maine late Tue/early Wed before finally
moving away on Wednesday mid-day. Rain will change to snow from
west to east as the column cools post-FROPA, setting up some lake-
enhanced/effect snow for areas east of Lakes Erie/Ontario and
upslope snow for the central Appalachians and into the Adirondacks
and Green/White Mountains. WPC probabilities for at least 4 inches
of snow are 20-50% in far western WY south of BUF, 50-90% in the
Adirondacks and Tug Hill Plateau, and 40-80% in the northern Green
and White Mountains into far northwestern Maine. Low (10-20%)
probabilities for at least 4 inches of snow are present over the
central Appalachians and northern Maine.


...Northwest Montana...
Day 3...

Strong height falls plunging southward out of southwestern Canada
late Wed will drive a cold front through Montana, setting up a
period of wintry weather. Northeasterly flow post-FROPA will
provide plenty of upslope enhancement into northwestern MT amid
ample lift in the column and lowering snow levels. Moderate to
perhaps heavy snow is likely along the Lewis and Flathead Ranges on
Wednesday with lighter snow extending southward and southeastward
into northwestern WY (continuing into Day 4). WPC probabilities for
at least 6 inches of snow are high (>70%) over the Lewis Range and
low (10-40%) into the Little Belts, Crazy Mountains, and into the
Absarokas.


...Central Sierra...
Day 3...

Meandering upper low west of California will finally move into
SoCal late Wednesday night/early Thursday morning, with some
downstream generally light precipitation into the Sierra. Snow
levels will be quite high (>8000ft) and there are low probabilities
(10-40%) of at least 4 inches of snow through 12Z Thu 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