Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
411 PM EST Fri Dec 14 2018

Valid 00Z Sat Dec 15 2018 - 00Z Tue Dec 18 2018


...Pacific Northwest to the Northern Rockies...
A potent northern stream trough will push across the Pacific
Northwest (north from northern CA) later tonight into Saturday as
a surface low crossing Vancouver Island and sets up a prolonged
period of onshore flow. The majority of precipitation will fall
early in the Day 1 period over the Coast Ranges and Cascades just
ahead of the cold front from this low. Snow elevations will be
4000-5000ft with high probabilities for four inches of snow above
this level in far northern CA and western OR/WA.

Shortwave ridging results in light to no precip later tonight
through Saturday. The trough from a deep low over the Gulf of
Alaska brings the next round of precip to the Pac NW late
Saturday. However, tropically sourced moisture will have rather
high snow elevations (6000-7000ft) ahead of the mid-level trough
axis which does not reach the coast until Monday. The greatest
moisture fetch is into far northern CA with the northern CA
Cascades having moderate probabilities for six inches of snow for
Day 3.

...Northeast U.S...
There are a few signs pointing to the possibility of a period of
light freezing precipitation across parts of New York into
southern New England as warm air north of a low gets pushed inland
before cold high pressure moves away.  In addition, light snow
will brush the area as a weak wave in the northern stream scoots
by. The key will be how far north the system is when it emerges
over the water.  At this point, the probabilities from WPC show
only a marginal risk of 4 inches of snowfall and less than 10
percent risk of significan icing in this region.

Bann