Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EST Sat Nov 14 2020

Valid 12Z Sat Nov 14 2020 - 12Z Tue Nov 17 2020


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

GOES-16 mid-level water vapor imagery depicts a well-defined,
neutrally tilted, upper trough axis currently moving east from NV
into UT with an upper ridge just off the West Coast. The trough
will shift east of the Rockies today. Associated mountain snows
over CO/WY will continue this morning with snow levels currently
around 6000ft dropping to 4000ft as snow tapers off. Day 1 snow
probabilities for 6 or more inches after 12Z light to moderate
across the highest northern CO Rockies.

Meanwhile, the next shortwave trough will shift into central BC
tonight on strong zonal flow shifting elevated Pacific moisture
across the Northwest CONUS on the back side of the ridge this
afternoon through Monday when the next low/trough approaches the
Northwest. A frontal zone will provide a focus for precip with
high snow levels over western WA/OR tonight, southern OR/far
northern CA then through Sunday night before shifting north
through western WA Monday ahead of the approaching low/trough. Day
1/1.5 snow probabilities for 6 or more inches are high for the
WA/OR Cascades, Blue Mtns of northeast OR, central and northern
ID, and northwest WY. Day 3 snow probabilities for 6 or more
inches are moderate and limited to the WA Cascades.

...Northern Maine...
Day 2...

The upper trough associated with the system currently moving
across the West will continue to move quickly across the U.S.
through the weekend, with a negatively-tilted upper trough moving
across the Midwest/Great Lakes into Quebec Sunday night.  Cold air
north of a developing secondary low lifting across the Northeast,
will support a period of snow across northern New York and New
England late Sunday into early Monday, with 30 percent Day 2
probabilities for 6 or more inches for far northern Maine.


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

Jackson