Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
331 PM EDT Wed Sep 25 2019

Valid 00Z Thu Sep 26 2019 - 00Z Sun Sep 29 2019

...Western U.S....

...A prolonged higher elevation heavy snow event focused on
eastern slopes of the northern Rockies in MT begins late Friday
and continues through the weekend...

Deep low pressure currently over southwestern Alaska shifts down
the AK/BC coast to the Pacific Northwest into Friday before
stalling over interior WA/OR Saturday. Surface low pressure shifts
east across northern MT Thursday brings an initial wave of cold
air to the northern Rockies that is reinforced by height falls
from the upper low pushing into WA after 12Z on Friday. Surface
high pressure centered near the northern BC/Alberta border that
extends on a surface ridge to northern MN and a lee trough/low
over WY/eastern MT Saturday provides a broad area of northeasterly
flow which is upslope for north-central MT. Moisture streaming up
the Great Plains with origins over the Gulf of Mexico arrive in MT
Friday night and aids heavy precip rates particularly for eastern
slopes of the Rockies in MT until the low lifts out in the Sunday
night timeframe. Several feet of snow are possible above about
5000ft.

Given that the heavy precipitation starts on Day 3 there is still
uncertainty with timing and intensity. Also, the threat continues
well into Day 4, so the scope of the event will be better
understood starting tomorrow.

The probability of significant icing is less than 10 percent.

The WPC WWD has begun early due to this significant snow event.
The desk will remain open on day shifts only for this event. The
WPC WWD is scheduled to resume normal operations on Oct 3.

Jackson