Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
446 AM EST Sun Nov 24 2019

Valid 12Z Sun Nov 24 2019 - 12Z Wed Nov 27 2019

Day 1...

...Northeast...
Ongoing precipitation over the Mid-Atlantic and Northeast will
continue to spread north as the associated upper level shortwave
swings east from the Ohio valley into the Mid-Atlantic Sunday
morning.  Models show the upper trough assuming a negative tilt
with a closed center developing as it lifts along the New England
coast later today.  Mixed precipitation, including wet snow is
forecast to fall northwest of a deepening surface low tracking
from the New Jersey coast to the Gulf of Maine on Sunday. 
Beginning Sunday morning and continuing through the afternoon
hours, low-to-mid level frontogenesis in combination with strong
upper forcing is expected to support enhanced precipitation rates
and raise the threat for locally heavier snowfall accumulations
extending from northern New Hampshire across northern Maine.

...Pacific Northwest to the Northern Rockies...
Beginning Sunday and continuing into early Monday, a series of
low-amplitude shortwaves embedded with fast northwest flow are
expected to produce several inches of snow across the higher peaks
of the northern Cascades, with generally lighter amounts expected
farther east over the Blue Mountains and northern Rockies.

Day 2...

...Pacific Northwest the Northern Rockies...
An amplifying shortwave centered along the leading edge of strong
upper jet is expected to dive southeast across California into the
Great Basin and Four Corners region on Monday.  Ongoing
precipitation over the Northwest early Monday is expected to
continue while heavier amounts begin to shift farther south and
snow levels drop significantly across the Oregon Cascades on
Monday.

...Central Rockies to the High Plains...
As the previously noted shortwave continues to dive southeast into
the Great Basin, expect locally heavy snows to develop over the
Uintas and northern Wasatch Monday morning.  Then by late Monday
afternoon and continuing into the evening and overnight hours,
snows will develop farther east across northern Colorado,
southeastern Wyoming and western Nebraska.  As low pressure
develops east of the Rockies, increasing upslope flow north of the
low, along with low-to-mid level frontogenesis, is expected to
support heavy snowfall accumulations from the Laramie and Medicine
Bow Mountains and the Front Range eastward into High Plains -
extending into the southwestern sections of the Nebraska Panhandle
Tuesday morning.

Day 3...

...Oregon/California into the Great Basin...
The global guidance is in generally good agreement, showing a
rapidly deepening cyclone dropping southeast toward the
Oregon/California border on Tuesday.  Most of the guidance shows
the surface low dropping below 980mb as it nears the coast Tuesday
afternoon.  Beginning late Tuesday and continuing into early
Wednesday, powerful onshore flow will support widespread moderate
to heavy precipitation across southern Oregon and northern
California.  With snow levels near the coast, widespread heavy
snowfall accumulations are expected from the southern Cascades and
the coastal ranges of southwestern Oregon and northwestern
California to the Sierra.  By Wednesday morning, widespread
snowfall accumulations of 12-24 inches, with locally heavier
amounts can be expected across these areas.  Lighter accumulations
will extend farther east into eastern Oregon and northern Nevada.

...Central Plains to the Upper Great Lakes...
The upper trough forecast to move across the central Rockies early
Tuesday is expected to amplify, with a closed low developing as it
moves east across the central Plains on Tuesday.  Models show the
upper system continuing to deepen with a strong surface cyclone
developing and tracking northeast from central Plains and lower
Missouri valley late Tuesday, toward the Great Lakes Wednesday
morning.  In addition to the strong upper forcing, low-to-mid
level frontogenesis will likely support a stripe of moderate to
locally heavy snows northwest of the low center.  The general
consensus of the overnight models places the axis of heavier
amounts from northeastern Colorado to the eastern U.P. of Michigan.

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

Pereira