Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Sat Apr 27 2024

Valid 00Z Sun Apr 28 2024 - 00Z Wed May 01 2024

...Pacific Northwest and Northern Rockies...
Days 1-3...

A longwave trough and associated surface low over the Northeast
Pacific will dig southeastward from the Alaska Panhandle down to
the Pacific Northwest by D3/Tuesday. This pattern will make for a
prolonged period of onshore flow from the northwest into the
Olympics and Cascades, along with increasingly colder air. The
broad flow pattern from Alaska and not from the tropics will hold
amounts well shy of extreme levels, but nonetheless the constant
influx of Pacific moisture will result in multiple days of snow
into the higher elevations, starting near the coast D1, then
gradually spreading inland into ID, MT, and WY by D3. The
increasingly colder air will also allow snow levels to gradually
drop with time down to as low as 2,500 ft by Monday. This will
eventually transition the precipitation type through the various
passes from rain to snow.

In the upper levels, a very slow moving jet streak will gradually
move into OR and eventually southern ID & WY by Tuesday evening.
This will keep areas north of that axis in the favorable LFQ, which
will support the ongoing snow in the mountains and passes. As
several embedded shortwaves move eastward on D1 and D2, followed by
the upper trough itself by D3, there will be periods of heavier
snow all across the Intermountain West.

WPC probabilities for more than 4 inches increase above 70% into
the higher elevations of both the WA and OR Cascades, as well as
the Salmon River Mountains and Bitterroots by Tuesday. Lower values
above 40% extend to the mountains around Glacier and Yellowstone
NPs Tuesday night. Hazardous travel is possible through the passes
from Snoqualmie tonight to western MT and WY by Tuesday.

The probability of significant icing is less than 10 percent.

Wegman