Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 PM EST Fri Jan 04 2019

Valid 00Z Sat Jan 05 2019 - 00Z Tue Jan 08 2019


...New England...
Days 1-2...

A deep upper low with developing surface low will lift northeast
from the Mid-Atlantic states tonight to near Nova Scotia late
Saturday. At the same time, a northern stream shortwave will dig
through southeast Canada, with the interaction between these two
features drawing moisture northward into interior New England.
Above normal temperatures will keep precipitation rain south from
southern New England. A stripe of light freezing rain can be
expected northeast from the Catskills late tonight through
Saturday morning. WPC probabilities are low to moderate for a
tenth inch of ice over southern VT/NH though precip will have to
overcome dry air first limiting the potential there.

Saturday night into Sunday...Lake enhanced snow can be expected
off Lake Ontario in the Tug Hill Plateau and Adirondacks with
upslope flow for northern VT and wrap around snow for northern ME.
Low to moderate WPC probabilities for two inches are across these
areas.


...Western U.S....
Days 1-3...

A strong low will reach the CA/OR border Saturday preceding a deep
trough moving onshore Saturday night. Snow levels rise ahead of
this feature, but will fall behind the associated cold front which
will move into California on Saturday. Significant moisture within
a Pacific Jet maximum will advect onshore, and intense lift within
the left exit region of the jet max combined with increasing 700mb
flow will produce heavy snow from the Sierra Nevada to the OR
Cascades. The heaviest snow is likely in the Sierras where
low-level winds will be orthogonal to the ranges to produce
efficient upslope enhancement, and WPC probabilities are moderate
in northern CA for Day 1 then moderate to high for 12 inches on
each of Days 2 and 3 for the High Sierra and moderate across
higher elevations of the Mountain West.

As the trough shifts eastward during Sunday, moisture and
associated heavy snow will spread into the rest of the Mountain
West, with heavy snow likely as far south as the Mogollon Rim of
AZ, and as far north as the Canadian Rockies. Snow levels will
fall to as low as 4000 feet in AZ/NM, with 1000-2000 feet
widespread from Utah and points north. WPC probabilities show a
moderate risk for 8 inches in the highest terrain of the Four
Corners states, with widespread high probabilities for 4 inches
elsewhere.


...Upper Midwest...
Day 3...

An upper trough moves east across the Rockies Sunday night with
the associated surface low crossing the Canadian Prairies through
Monday. A warm front will lift across the Midwest WAA Sunday night
with strong warm air advection causing precipitation to overspread
the region. The antecedent column is not very cold, so the
low-level thermal advection will cause much of the precipitation
to be rain south of MN/WI/MI. Areas of these three states are
expected to be cold enough initially for freezing rain with a
wintry mix of snow/sleet/freezing rain farther north. Moderate
precip rates in this southerly flow can be expected with high WPC
probabilities for four inches around Lake Superior.


Jackson