621
FOUS11 KWBC 211821
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
221 PM EDT WED OCT 21 2026
VALID 00Z THU OCT 22 2026 - 00Z SUN OCT 25 2026
..SOUTHERN SIERRA NEVADA
DAYS 1-2...
THE CLOSED UPPER-LOW OFF THE SOUTHERN CA COAST WILL DIRECT A PLUME
OF TROPICAL MOISTURE AT THE SOUTHWEST U.S. THIS EVENING AND INTO
THURSDAY. SOME OF THIS MOISTURE SOURCE WILL BE DIRECTED AT THE
SOUTHERN SIERRA NEVADA WHERE A COMBINATION OF TOPOGRAPHICALLY-
INDUCED UPSLOPE FLOW AND SYNOPTIC SCALE SUPPORT IN THE FORM OF A
120KT+ 250MB JET STREAK WILL AID IN ENHANCED PRECIPITATION RATES
AND MOUNTAIN SNOW. LATEST 12Z HREF/REFS PROBABILISTIC GUIDANCE
SHOWS LOW-TO-MODERATE CHANCES (30-50%) FOR >1"/HR SNOWFALL RATES
OVERNIGHT AND INTO THURSDAY MORNING. THESE SNOWFALL RATES WILL BE
OBSERVED HIGHER UP IN THE SOUTHERN SIERRA NEVADA WITH MOST AREAS
ABOVE 9,000FT WITNESSING THESE POTENTIAL SNOWFALL RATES. SNOW IS
EXPECTED TO TAPER OFF THURSDAY NIGHT AS THE UPPER LOW SHIFTS TO THE
NORTH-NORTHEAST. THE PROBABILISTIC PRECIPITATION PORTAL (PPP) DOES
SHOW MODERATE- TO- HIGH CHANCES (40-80%) FOR SNOWFALL TOTALS >6"
ABOVE 9,000FT IN ELEVATION, WITH LOW CHANCES (10-30%) FOR SNOWFALL
AMOUNTS EXCEEDING 12" ABOVE 11,000FT. THE WSSI SHOWS MINOR IMPACTS
ARE ANTICIPATED FOR ELEVATIONS AT/ABOVE 9,000FT, INDICATING WINTER
DRIVING CONDITIONS ARE EXPECTED AND TO EXERCISE CAUTION WHEN
DRIVING IN AT THOSE ELEVATIONS.
..NORTHERN & CENTRAL ROCKIES
DAYS 2-3...
THE SAME CLOSED LOW RESPONSIBLE FOR THE HEAVY SNOW IN THE SIERRA
NEVADA WILL WORK IN TANDEM WITH UPPER-LEVEL RIDGING OVER THE
SOUTH CENTRAL U.S. TO PROJECT AN IMPRESSIVE IVT INTO THE
INTERMOUNTAIN WEST. BY 18Z THURSDAY, THE IVT IS SURPASSING 500
KG/M/S IN NORTHEASTERN AZ AND EASTERN UT, WHICH IS SURPASSING THE
MAXIMUM OBSERVED VALUES IN THE CFSR CLIMATOLOGY (1979-2009). THIS
HIGHLY ANOMALOUS MOISTURE TRANSPORT WILL UPSLOPE INTO VARIOUS
MOUNTAIN RANGES THROUGHOUT THE INTERMOUNTAIN WEST (SAN JUAN, NV
GREAT BASIN RIDGE, WASATCH, WIND RIVER, TETONS, ABSAROKA). MOST
ACCUMULATIONS WILL BE ON THE MINOR SIDE GIVEN THE LACK OF A
SUFFICIENTLY COLD AIR-MASS AND HIGH SNOW-LEVELS. IN FACT, SNOW
LEVELS START ABOVE 13,000FT TONIGHT ACROSS THE SAN JUANS AND EVEN
OVER 11,000FT OVER THE NORTHERN ROCKIES ONCE PRECIPITATION ENTERS
THE REGION FRIDAY MORNING. SNOW LEVELS DECLINE BY FRIDAY EVENING TO
AROUND 5,000-6,000FT IN THE NORTHERN ROCKIES AND 8,000FT-10,000 FT
IN THE CENTRAL GREAT BASIN/ROCKIES. STILL, THURSDAY IS THE SNOWIER
DAY FOR THE SAN JUAN MOUNTAINS, WHILE FRIDAY IS THE SNOWIER DAY
FOR THE MOUNTAINS RANGES ACROSS UT, NV, ID, SOUTHWEST MT, AND
WESTERN WY AS THE MOISTURE SURGE CROSSES THE REGION.
LATEST PPP SHOWS LOW-TO-MODERATE CHANCES (30-50%) FOR SNOWFALL
TOTALS >6" IN THE MORE REMOTE HIGH ELEVATIONS OF THE SAN JUAN,
TETON, WIND RIVER, AND ABSAROKA RANGES. LOCALIZED SNOWFALL AMOUNTS
APPROACHING 12" IN THE PEAKS ON THE SAN JUAN MOUNTAINS ARE
POSSIBLE, ESPECIALLY WHERE HOURLY SNOWFALL RATES >1"/HR OCCUR. THE
WSSI-P SHOWS <20% ODDS FOR MODERATE IMPACTS THROUGHOUT THE
INTERMOUNTAIN WEST. SOME TRAVEL DISRUPTIONS AT PASS LEVELS ARE
POSSIBLE GIVEN THE MODERATE-TO-HIGH CHANCES (50-80%) FOR MINOR
IMPACTS IN PARTS OF THE SAN JUAN, TETONS, AND ABSAROKA MOST
NOTABLY.
THE PROBABILITY OF SIGNIFICANT ICE ACROSS THE CONUS IS LESS
THAN 10 PERCENT.
MULLINAX/SNELL
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