Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 AM EST Sun Nov 19 2023

Valid 12Z Sun Nov 19 2023 - 12Z Wed Nov 22 2023

...Cascades to the Central Rockies...
Day 1...

A strong cold front will continue to push southward and eastward
through the Great Basin today with lowering snow levels in its
wake. Remnant lingering moisture over the region will help fuel
widespread snow in the mountains that will lower into some valleys
later today into the evening. Trailing elongated/sheared upper
vort max will bring the last round of snow to the Cascades today
before tapering by late evening. Additional accumulation of 4-8
inches is likely (>70% chance) above about 5000ft over the WA/OR
Cascades and into the Idaho ranges. Closer to the front, the
Wasatch and western Uintas will see the most snow on day 1 with
probabilities of at least 6 inches greater than 50% above about
8500ft. As the upper trough closes off again over the central
Plains by the end of day 1, additional snowfall will spread across
the CO Rockies and especially the San Juans into the Sangre de
Cristos where WPC probabilities of at least 4 inches of snow are
30-80%.

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

A shortwave and surface cold front will track across the Northeast
today with periods of snow showers and brief lake effect snow east
of Lake Ontario. Areas of the northern VT may see a couple inches
of snow though WPC probabilities for more than 4 inches are
generally less than 10%.

Day 3...

The upper low exiting across the Plains on day 2 will weaken and
lift northeastward through the Ohio Valley on day 3, spreading
precipitation over the central Appalachians and into the
Northeast. Some light freezing rain or a mixture is possible on
the north side of the precipitation shield (Lower Michigan) as
well as along and just east of the Appalachian crest where
marginally cold air at the surface will lag behind milder air
driven in aloft on southwesterly flow (Laurel Highlands, northern
Blue Ridge, central PA, etc.) before turning over to rain. Farther
northeast, the colder air will be deeper and by late day 3 the
main surface low may weaken into the St. Lawrence valley as
another low forms and deepens near the DelMarVa, likely becoming
the dominant low by the end of the period (12Z Wed). By that time,
enough cold air may be held in across northeastern NY
(Adirondacks) across central and northern New England to support
light to moderate accumulations, continuing into day 4. Through
12Z Wed, WPC probabilities of at least 4 inches of snow are low
(10-40%) with the higher chances across central NH at this time,
but this is quite dependent on the track of the surface lows and
hand-off to coastal development.


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

Fracasso