Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
345 AM EST Thu Jan 30 2020

Valid 12Z Thu Jan 30 2020 - 12Z Sun Feb 02 2020


...Pacific Northwest to the Northern Rockies...
Days 2-3...

Relatively quiet winter weather will ramp up beginning late
Friday, and especially on Saturday. Although considerably moisture
will flood into the Pac NW on D2 /Friday/, snow levels associated
with a warm front will rise to 6000-8000 ft, such that only the
highest peaks of the Olympics and Washington Cascades will
experience any significant snow. However, a cold front draped from
low pressure moving into British Columbia Saturday will cause snow
levels to drop considerably, while enhanced moisture streams
eastward into the western CONUS from a robust Pacific jet streak
and confluent mid-level flow. The combination of enhanced PWAT of
over 0.5" and 850mb flow rising to 50 kts will advect copious
moisture in conjunction with the lowering snow levels. This will
spread heavy snow into the Olympics, Cascades of Washington and
Oregon, and further east into the Northern Rockies on D3. WPC
probabilities are high for 8 inches in the Washington Cascades,
and moderate in the other ranges mentioned. Snow levels will drop
considerably by the end of the period, and even some of the
Valleys of WA/OR may see light accumulation by Sunday morning.

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

Weiss