Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
451 AM EST Sat Nov 23 2019

Valid 12Z Sat Nov 23 2019 - 12Z Tue Nov 26 2019


Days 1-3...

...Ohio Valley/Central Appalachians to the Northeast...
An upper low centered over the central Plains Saturday morning is
expected to transition to an open wave as it moves progressively
east through the mid Mississippi valley early in the day, before
reaching the Ohio valley by late Saturday.  Models continue to
show mixed precipitation, with light snow and ice accumulations
developing on the northwest side of surface low lifting northeast
into the Ohio valley Saturday afternoon and evening.

On Sunday, the upper trough is forecast to assume a negative tilt
as it moves across the Northeast - driving a deepening surface low
northeast from the New Jersey coast to the Gulf of Maine. 
Overnight models have trended notably deeper and farther to the
north with this system - resulting in higher snowfall and ice
accumulations across portions of Upstate New York and northern New
England on Sunday.  While marginal boundary layer temperatures are
expected to help keep accumulations in check, strong upper forcing
along with low-to-mid level frontogenesis have raised the
probabilities for significant snow accumulations across the higher
elevations of northern New England.  Should this trend hold,
expect to see these probabilities further increase in subsequent
model runs.  By early Monday as the low tracks progressively
northeast into the Canadian Maritimes, expect snows to diminish
from west to east across northern New England.

...Pacific Northwest and Northern Rockies...
A shortwave trough diving southeast into the Northwest is forecast
to bring colder air and the potential for several inches of snow
to some of the higher peaks of the northern Cascades and northern
Rockies on Sunday.  This will be followed by a second shortwave
digging farther south, carving out an amplified upper trough
centered over the Great Basin on Monday.  Begining Monday and
continuing into early Tuesday - as snow levels drop precipitously,
a prolonged period of strong onshore flow will help support heavy
snows across the Olympics and Cascades, as well as the Blue
Mountains in northeastern Oregon and far southeastern Washington.

..Central Rockies and High Plains...
The upper trough amplifying over the Great Basin on Monday is
expected to translate east into the central Rockies late Monday
into early Tuesday.  This will likely produce some locally heavy
amounts across the Unitas and northern Wasatch Monday morning. 
Then with increasing dynamics and upslope flow, snows are expected
to develop farther east across Colorado and Wyoming before
extending into western South Dakota and Nebraska.  Upslope winds
will likely favor locally heavy totals across the southeastern
Wyoming and northern Colorado ranges.

The probability of significant icing (0.25-inch) is less than 10
percent.

Pereira