258
FOUS11 KWBC 101900
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT FRI APR 10 2026
VALID 00Z SAT APR 11 2026 - 00Z TUE APR 14 2026
..SIERRA NEVADA THROUGH THE NORTHERN ROCKIES
DAYS 1-3...
AN UPPER LOW OPENING UP OFF THE NORTHERN CA COAST WILL WEAKEN, BUT
BE QUICKLY REPLACED BY AN EVEN MORE POTENT UPPER LOW DIVING SOUTH
FROM ALASKA TO TAKE UP RESIDENCE IN A SIMILAR POSITION BY 00Z
SUNDAY. THIS DEEPER LOW IS THEN FORECAST TO DROP SLOWLY E/SE TO
COME ONSHORE THE BAY AREA BY 00Z MONDAY, BEFORE OPENING INTO A
LONGWAVE POSITIVELY TILTED TROUGH CENTERED OVER THE GREAT BASIN BY
THE END OF THE FORECAST PERIOD.
FORCING FOR ASCENT WILL MAXIMIZE DOWNSTREAM OF THIS SECONDARY UPPER
LOW AS MID-LEVEL DIVERGENCE AND HEIGHT FALLS OVERLAP INTO CENTRAL
AND NORTHERN CA. THIS WILL BE ACCOMPANIED BY THE LFQ OF A
SHARPENING SUBTROPICAL JET STREAK ROTATING AROUND THE UPPER LOW,
AND THE OVERLAP OF THESE FEATURES IS EXPECTED TO DRIVE CONSIDERABLE
SYNOPTIC LIFT ACROSS THE REGION, WITH OROGRAPHIC ENHANCEMENT LIKELY
INTO THE SIERRA AND NORTHERN CA TERRAIN DUE TO THE ONSHORE 700MB
FLOW. THIS LIFT WILL ACT UPON A RAPIDLY MOISTENING COLUMN AS IVT
SURGES ONSHORE (90% CHANCE FOR AT LEAST 250 KG/M/S) LEADING TO PW
ANOMALIES REACHING +1 TO +2 SIGMA ACROSS MUCH OF CA.
THIS WILL RESULT IN AN AREA OF EXPANDING PRECIPITATION, ESPECIALLY
00Z/SUN TO 12Z/MON OVER CA, WITH SOME MODEST SPILLOVER AND SPREAD
OF PRECIPITATION INTO THE ROCKIES AND GREAT BASIN THEREAFTER.
HOWEVER, THE HEAVIEST PRECIP IS EXPECTED IN THE SIERRA AND NORTHERN
CA TERRAIN, WHICH ARE ALSO THE AREAS THAT WILL EXPERIENCE HEAVY
SNOWFALL AS THEY WILL BE ABOVE THE FALLING SNOW LEVELS. AS FAR AS
SNOW LEVELS, THEY ARE EXPECTED TO BEGIN AROUND 6000-8000 FT, BUT
WILL FALL QUICKLY THROUGH SUNDAY AND INTO MONDAY AS THE UPPER LOW
MOVES ONSHORE, BECOMING AS LOW AS 4500 FT, BUT STEEP LAPSE RATES
BENEATH THE UPPER LOW MAY CAUSE SNOW TO ACCUMULATE BELOW 4000 FT AS
REFLECTED BY THE NBM 10TH PERCENTILE.
HEAVY SNOW RATES REACHING 1-3"/HR AS PROGGED BY THE WPC PROTOTYPE
SNOWBAND TOOL IN THE TERRAIN COMBINED WITH 24-36 HOURS OF MODERATE
TO HEAVY SNOW WILL RESULT IN SIGNIFICANT ACCUMULATIONS THAT HAVE A
HIGH RISK (>70% CHANCE) OF REACHING AT LEAST 18", WITH LOCALLY 2-3
FEET POSSIBLE (30-70% CHANCE), HIGHEST IN THE HIGH SIERRA. THIS
WILL CREATE MODERATE TO MAJOR (70% CHANCE OF MAJOR) IMPACTS ACROSS
THE SIERRA INCLUDING MANY OF THE IMPORTANT PASSES.
LESSER, BUT STILL SIGNIFICANT SNOW MAY EXPAND ACROSS THE GREAT
BASIN AND INTO PARTS OF THE NORTHERN ROCKIES, LEADING TO POCKETS OF
WPC PROBABILITIES EXCEEDING 30% FOR 8+ INCHES IN THE HIGHEST
ELEVATIONS OF NV, SOUTHERN OR, AND PARTS OF ID.
THE PROBABILITY OF SIGNIFICANT ICING FOR DAYS 1-3 ACROSS THE CONUS
IS LESS THAN 10 PERCENT.
WEISS
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