FOUS11 KWBC 140709
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
309 AM EDT Mon Oct 14 2024

Valid 12Z Mon Oct 14 2024 - 12Z Thu Oct 17 2024

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

An anomalous upper level trough over the Northeast will lead to a
strengthening cyclone over northern New England this morning. The
850mb low positioned over Upstate New York will track north and
east through the Green and White mountains by this afternoon. To
the north and west of the 850mb low, a surge in both moisture and
NW winds will result in a stronger upslope component into the
Adirondacks, Green, and White mountains throughout the day. In
addition to the sufficient upper level ascent, an ari-mass that
is quite cold by mid-October's climatology will support sub-
freezing boundary layer temps for in the northern Appalachians. Locally
heavy snowfall rates are expected with 0.5-1"/hr rates possible in
the tallest peaks of the Adirondacks this morning and afternoon
according to the 00Z HREF on WPC's Snowband Probability Tracker. As
the storm tracks into Quebec this evening, snow will taper off and
be limited to just snow showers through Tuesday morning. Another
round of snow is likely to occur Tuesday late morning and through
the afternoon as a trough axis pivoting on the back side of the
storm system in eastern Quebec brings about an additional surge of
low- mid level moisture. In addition, steep lapse rates could
trigger potent snow showers, especially in the higher terrain of
northern New England above 2,000ft. Snow showers look to linger in
the northern Appalachians until Wednesday morning when the trough
axis moves east and off the New England coast.

Any locally heavy snowfall totals (>4" would likely be confined
to elevations above 2,000ft in the Adirondacks, Green, and White
mountains. WPC probabilistic guidance does depict some low-
moderate chances (20-40%) for >6" of snowfall in the tallest
>3,000ft peaks of the Adirondacks. Below 2,000ft, snowfall amounts
will struggle to top 2" in the 1,000-2,000ft elevation layer, with
mainly a coating to 1" in the elevations below 1,000ft. Given this
snowfall is the first of the season for parts of the region,
motorists will be subjected to poor visibility and some snow
covered roads for the first time in months. The WSSI-P does show
low-moderate chances (20-40%) for Minor Impacts in parts of the
Adirondacks through Monday evening.

...Northwest...
Days 2-3...

A 500mb shortwave trough bringing with it a surge in 850-700mb
moisture and associated height falls will cause snow levels to
gradually drop to as low as 4,000ft by Wednesday. The air-mass is
not particularly cold for the time of year, so this setup favors
snowfall accumulation in the Olympics and Cascades to elevations
>5,000ft. WPC probabilities do suggest low-moderate chances
(20-40%) for >4" of snowfall on Wednesday along the windward side
of the Cascade Range at elevations >4,000ft. As 500mb heights and
snow levels continue to fall, some of the higher level Washington
passes may start to see accumulating snow by Wednesday night. The
potential for accumulating snowfall reaches the Northern Rockies
(the Bitterroots, Absaroka, and Tetons most notably) by early
Thursday morning. WPC probabilistic guidance suggests the Lewis
Range of western MT could see locally higher totals surpassing 4"
at elevations >7,000ft, while the other mountain ranges mentioned
are most likely to see their best accumulating snowfall above
8,000ft on Thursday.


The probability of significant ice across the CONUS is less than
10 percent.

Mullinax


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