Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 AM EST Sat Mar 06 2021

Valid 12Z Sat Mar 06 2021 - 12Z Tue Mar 09 2021


...Pacific Northwest/California to the Northern Rockies...
Days 1-3...
Frontal band precipitation moving inland across Northern
California is just reaching the eastern side of the San Joaquin
Valley, but will be winding down over for the northern Sierra
Nevada by 12Z (when Day 1 snow probabilities begin) as the
mid-level shortwave trough axis lifts northeast into the Great
Basin with veering low level flow in the approaching ridge cuts
off Pacific moisture.

A cold front from a low pressure system drifting south well off
the BC coast reaches the WA/OR/far northern CA coast late tonight
with snow levels around 2000ft. Organized precip/mountain snows
diminish as the front moves east and weakens on Sunday and onshore
flow backs southerly, cutting off moisture influx. The next
trough/frontal boundary from this low that should be off the WA
coast by Sunday night reaches the PacNW coast Monday with a decent
fetch of Pacific moisture pushing across far northern CA. Day 1.5
snow probabilities are high for 6 or more inches for the Olympics
and higher WA Cascades. Day 3 snow probabilities for 6 or more
inches are moderate for the Klamath/CA Cascades and
northern/central Sierra Nevada as well as some low probabilities
for the Wallowa Mtns of OR and the Salmon River/Clearwater Mtns of
ID.

...Eastern Great Lakes...
Day 1...
Deep northwesterly flow with embedded energy aloft and a saturated
DGZ will continue to support multi-band lake effect snow showers
south of Lake Ontario and eastern Lake Erie today. At least an
additional couple of inches of snow are likely, especially north
of and along the Finger Lakes region. Snows will diminish as a
surface high pressure shifts east into the region this evening.


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

Jackson