158
FOUS11 KWBC 271850
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
250 PM EDT TUE OCT 27 2026
VALID 00Z WED OCT 28 2026 - 00Z SAT OCT 31 2026
..CASCADES AND NORTHERN ROCKIES
DAYS 1-3...
AN AMPLIFYING UPPER LOW WILL ORGANIZE WEST OF BRITISH COLUMBIA AND
THEN DIG SLOWLY SOUTHWARD, REACHING TO A LATITUDE NEAR THE
OREGON/WASHINGTON BORDER BY THE END OF THE FORECAST PERIOD. AS
HEIGHTS FALL TO AROUND THE 10TH PERCENTILE (NAEFS), SPOKES OF
VORTICITY WILL SHED EASTWARD PROVIDING ASCENT FROM THE PACIFIC
NORTHWEST INTO THE NORTHERN ROCKIES. THESE WAVES OF VORTICITY WILL
COMPLEMENT MID-LEVEL DIVERGENCE OCCURRING DOWNSTREAM OF THIS UPPER
LOW, AND A WEAK STATIONARY FRONT DRAPED WEST TO EAST NEAR THE
CANADIAN BORDER, LEADING TO WAVES OF SNOW ALL 3 DAYS OF THE
FORECAST PERIOD.
THE HEAVIEST SNOWFALL IS LIKELY ACROSS THE CASCADES D1 AND D2 WHEN
MID-LEVEL FLOW ORTHOGONAL TO THE CREST. PWS WILL BE NEAR NORMAL,
BUT IMPRESSIVE AND PERSISTENT OMEGA DRIVEN BY UPSLOPE NOTED VIA
REGIONAL CROSS SECTIONS WILL PROVIDE ASCENT FOR HEAVY SNOW,
ESPECIALLY IN THE UPWIND TERRAIN WEDNESDAY AND THURSDAY,. THIS WILL
LEAD TO SNOWFALL RATES THAT MAY ECLIPSE 1"/HR AT TIMES, ESPECIALLY
ABOVE 4000 FT, BUT WITH SOME LOWERING AS THE UPPER LOW MEANDERS
JUST OFF THE WA/OR COAST. TOTAL SNOWFALL IS LIKELY (>60% CHANCE) TO
BE ABOVE 12" IN THE HIGHER ELEVATIONS, BUT IMPACTFUL PASS-LEVEL
SNOW ACCUMULATION EXCEEDING 4" IS POSSIBLE (10% CHANCE AT
SNOQUALMIE, 60% CHANCE AT STEVENS) THROUGH THE EVENT LEADING TO
CHALLENGING TRAVEL.
FARTHER EAST, PERIODS OF SNOW WILL ALSO OCCUR ACROSS THE NORTHERN
ROCKIES FROM THE OKANOGAN HIGHLANDS THROUGH THE AREA AROUND GLACIER
NATIONAL PARK. SNOW LEVELS WILL SLOWLY DROP THROUGH THE PERIOD FROM
AROUND 5000 FT D1 TO AS LOW AS 3500 FT LATE D2, BUT THE HEAVIEST
ACCUMULATIONS ARE LIKELY D1 TO D1.5 DURING THE PERIOD OF LOWERING
SNOW LEVELS. WITH MODEST OVERALL TEMPERATURES, PRECIPITATION MAY
MIX AT TIMES EVEN UP TO 5000 FT WHICH IS REFLECTED BY POSITIVE SNOW
DEPTH CHANGE THAT IS MUCH LESS THAN ACCUMULATED SNOWFALL FROM THE
GLOBAL GUIDANCE. THIS INDICATES LOW SLR SNOWFALL, HOWEVER, LEADING
TO IMPACTS FROM SNOW LOAD AS REFLECTED BY WSSI-P THAT IS AS HIGH AS
20-30% FOR MODERATE IMPACTS.
THE PROBABILITY OF SIGNIFICANT ICE ACROSS THE CONUS IS LESS THAN
10 PERCENT.
WEISS
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