648
FOUS11 KWBC 201948
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
348 PM EDT TUE OCT 20 2026
VALID 00Z WED OCT 21 2026 - 00Z SAT OCT 24 2026
..SOUTHERN SIERRA NEVADA
DAYS 1-2...
AN ANOMALOUSLY DEEP CLOSED LOW SPINNING OFF THE COAST OF SOUTHERN
CA WILL DIRECT A PLUME OF TROPICAL MOISTURE FROM THE EASTERN
PACIFIC NORTHWARD INTO THE SIERRA NEVADA THROUGH MID TO LATE WEEK.
AS THE LOW APPROACHES THE COAST, A POTENT 120KT+ UPPER-LEVEL JET
STREAK WILL OVERSPREAD THE REGION, LEADING TO AN INCREASE IN BROAD
LARGE SCALE FORCING FOR ASCENT. THE MOISTURE COMBINED WITH
INCREASING DYNAMIC FORCING WILL LEAD TO WIDESPREAD MODERATE TO
OCCASIONALLY HEAVY HIGH ELEVATION MOUNTAIN SNOW FROM WEDNESDAY
EVENING/NIGHT THROUGH THURSDAY EVENING. AIDING PRECIPITATION
PRODUCTION WILL BE THE MODESTLY STRONG LOW TO MID LEVEL FLOW
FAVORABLY ORIENTED TO THE RUGGED TERRAIN OF THE SIERRA NEVADA,
WHICH WILL ALSO SUPPORT UPSLOPE-ENHANCED PRECIPITATION RATES. IN
FACT, THE 12Z HREF/REFS BOTH HIGHLIGHT THE POTENTIAL FOR BURSTS OF
HEAVIER SNOW WITH PROBABILITIES OF 20-40 PERCENT FOR >1"/HR
SNOWFALL RATES, MAINLY LATER WEDNESDAY NIGHT INTO THURSDAY MORNING.
WITH THAT BEING SAID, THE LACK OF A SUFFICIENTLY COLD AIR MASS
AHEAD OF THE LOW IN ADDITION TO THE LOW FILLING AND OPENING UP AS
IT LIFTS NORTHEASTWARD INTO THE GREAT BASIN THURSDAY INTO FRIDAY
WILL KEEP THE HEAVIEST SNOWFALL CONFINED TO ABOVE 9,000-10,000FT.
THE PROBABILISTIC PRECIPITATION PORTAL (PPP) DEPICTS MODERATE TO
HIGH CHANCES (40-80%) FOR SNOWFALL TOTALS >8" AND LOW TO MODERATE
CHANCES (20-50%) FOR SNOWFALL >12" AT ELEVATIONS ABOVE
9,000-10,000FT THROUGH THURSDAY NIGHT. THE WSSI-P SHOWS HIGH
CHANCES (>70 PERCENT) FOR MINOR IMPACTS AND LOW TO MODERATE CHANCES
(30-70 PERCENT) FOR MODERATE IMPACTS MAINLY ABOVE 10,000-11,000FT.
THE ENHANCED MOISTURE AND MARGINAL THERMALS IN PLAY WILL KEEP SLRS
MOSTLY BELOW 11:1, WHICH WILL MAKE FOR A HEAVY, WET SNOWFALL IN
THE SIERRA NEVADA.
AS THE SYSTEM MOVES INTO THE NORTHERN INTERMOUNTAIN WEST/ROCKIES
THURSDAY NIGHT INTO FRIDAY, LOCALLY HEAVY SNOW WILL BE POSSIBLE
ACROSS SOME OF THE HIGHER ELEVATIONS OF SOUTHWEST MT, WESTERN WY, SOUTH-
CENTRAL ID, AS WELL AS THE EASTERN UINTAS IN NORTHEAST UT AND THE
SAN JUANS IN SOUTHWEST CO.
THE PROBABILITY OF SIGNIFICANT ICE ACROSS THE CONUS IS LESS THAN 10
PERCENT.
MILLER
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