Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 PM EST Sat Nov 18 2023

Valid 00Z Sun Nov 19 2023 - 00Z Wed Nov 22 2023

...Cascades to the Central Rockies...
Days 1-2...

An initial shortwave trough that will be weakening through tonight
will produce snow across the Sierra and Great Basin and eventually
into the central Rockies where precipitable water values will
remain elevated for this time of year.  A second a stronger trough
along with a relatively strong surface cold front will drop across
the Pacific Northwest tonight, and this is expected to result in a
2000-3000ft reduction in snow levels from Saturday.  Some of the
passes over the region will likely have a transition from rain to
snow, as snow levels fall to around 3000-4000 feet as the
precipitation winds down from northwest to southeast late Sunday
into Monday.  Terrain enhanced flow and mid-upper diffluence will
produce moderate snow totals in the Oregon Cascades, and extending
to the Blue Mountains and central Idaho ranges as the system
tracks southeastward.  Over Colorado, the strongest height falls
move in on Sunday into early Monday as the cold front weakens and
then reforms over the High Plains in response to the mid-level
trough closing off.  Several inches of snow are likely over the
Colorado Rockies into the San Juans and Sangre de Cristos into
northern New Mexico.  The greatest snowfall totals through Monday
night are expected to be across the Washington and Oregon
Cascades, the central Sierra, Blue Mountains of Oregon, the
Wasatch, and the Uinta Mountains, where snowfall totals could
locally exceed 12 inches.


...Northeast...
Day 1...

A shortwave and surface cold front will track across the Northeast
on Sunday with periods of snow showers for the higher elevations
of the Adirondacks to central Maine.  Most areas that are affected
by this should get less than 3 inches of accumulation, though WPC
probabilities for more than 4 inches are under 10%.  Dry weather
returns to the region by Sunday night and Monday as high pressure
from Canada builds in.

Day 3...

A developing low pressure system over the Central U.S. Monday is
progged to track east across the Ohio Valley on Tuesday.  There
will be a broad corridor of warm air advection to the east of this
low, with widespread rainfall developing across the
central/southern Appalachians and into the Mid-Atlantic.  A cold
Canadian surface high will initially be in place across New
England through early Tuesday, and this will likely provide enough
low level sub-freezing temperatures to support a brief period of
freezing rain and/or sleet at the onset of this precipitation from
east-central West Virginia and central Pennsylvania to central New
York, before a changeover to a cold rain.  This may start off as
snow across the Adirondacks where the cold air layer will
initially be deeper. 



For Days 1-3, the probability of significant icing (at least
0.25") is less than 10 percent.

Hamrick