783
FOUS11 KWBC 092027
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
427 PM EDT FRI OCT 9 2026
VALID 00Z SAT OCT 10 2026 - 00Z TUE OCT 13 2026
..NORTHERN ROCKIES
DAYS 1-3...
MID-LEVEL LOW IS APPARENT IN SATELLITE IMAGERY OVER EAST-CENTRAL
BRITISH COLUMBIA WITH A POSITIVELY TILTED TROUGH EXTENDING
SOUTHWEST OVER WESTERN WASHINGTON. A REINFORCING SHORTWAVE TROUGH
SHIFTS DOWN THE PACIFIC NORTHWEST COAST SATURDAY, PROMOTING A NEW
MID-LEVEL LOW OVER INTERIOR WASHINGTON/OREGON THAT DRIFTS SOUTH TO
THE GREAT BASIN INTO TUESDAY. AT THE SURFACE, A STRONG LEE-SIDE
CYCLONE IN SOUTHERN ALBERTA WILL SHIFT SOUTHEAST INTO THE DAKOTAS
TONIGHT AND SUPPRESSES SOUTH/EAST THROUGH SUNDAY AS HIGH PRESSURE
SHIFTS DOWN THE CANADIAN ROCKIES INTO WEST-CENTRAL MONTANA.
PRECIPITATION, BANDED AT TIMES, BEGINS TONIGHT OVER NORTHWEST
MONTANA AS MAINLY RAIN, BUT WILL TRANSITION TO SNOW AS SNOW LEVELS
CRASH FROM 8000-9000 FEET THIS EVENING TO 3000 FEET BY SATURDAY
AFTERNOON. SNOW BANDS ARE EXPECTED TO INCREASE IN COVERAGE AND
INTENSITY THROUGH SATURDAY OVER WEST-CENTRAL MT INTO NORTH-CENTRAL
ID. THERMODYNAMIC PROCESSES WILL COOL THE COLUMN QUICKER IN THE
HEAVIER BANDS, ALLOWING THE SNOW LEVEL TO REACH VALLEY FLOORS BY
THE MID AFTERNOON - EVEN IN AREAS LIKE GREAT FALLS WHERE THE
CURRENT TEMPERATURE IS IN THE LOW 80S. THE 12Z HREF INDICATES
OROGRAPHICALLY FORCED SNOW RATES APPROACH 1"/HR. DAY 1.5 SNOW
PROBS ENDING AT 12Z SUNDAY ARE 50-80% FOR >6" ALONG THE EASTERN
SLOPES OF THE LEWIS AND FLATHEAD RANGES AND 50-70% FOR THE
BIG/LITTLE BELTS, BIG SNOWY MTNS, AND THE ANACONDA RANGE.
THE COLD AIR SHIFTS SOUTH THROUGH THE REST OF WESTERN MONTANA
THROUGH SUNDAY MORNING WITH ADDITIONAL SNOW BANDS DEVELOPING DOWN
TO THE WYOMING BORDER. THIS WILL BE A HEAVY/WET SNOW WITH WSSI-P
MODERATE SNOW LOAD IMPACT PROBS IN THE 30-50% RANGE FOR SOUTHERN MT
RANGES SUNDAY INTO MONDAY.
LATE SUNDAY INTO MONDAY, THE REMNANTS OF RACHEL ARE EXPECTED TO
QUICKLY CROSS FROM THE GREAT BASIN. RENEWED FRONTOGENETIC FORCING
BENEATH WELL DEFINED RIGHT ENTRANCE ASCENT COULD BRIEFLY
REINVIGORATE SNOWFALL RATES IN THE NORTHERN ROCKIES, ALTHOUGH THERE
IS UNCERTAINTY WITH RESPECT TO THERMAL PROFILES IN THE REGION TIED
TO THE TRACK OF RACHEL'S REMAINS. RATES UP TO 1"/HR CAN BE
EXPECTED TO CONTINUE IN THE STRONGER BANDS. DAY 2.5 SNOW PROBS FOR
>6" ARE 50-80% FOR MOST WEST-CENTRAL AND SOUTHWESTERN MONTANA
RANGES INCLUDING THE CRAZY, RED LODGE PORTION OF THE NORTHERN
ABSAROKAS, AND GALLATIN.
THE KEY TO THIS EVENT REMAINS THE PLACEMENT OF MESOSCALE BANDING
WHICH WILL OVERCOME THE MARGINAL THERMAL PROFILES DOWN TO VALLEY
FLOORS WHERE THEY OCCUR.
SNOW LEVELS REMAIN AROUND 10,000FT OVER WYOMING, SO ONLY THE
HIGHEST ABSAROKAS AND THE WIND RIVER RANGE. CONSIDERABLE PRECIP
OVER WY IS EXPECTED WITH FEET OF SNOW EXPECTED ABOVE THE SNOW LEVEL
THROUGH THE EVENT.
..SIERRA NEVADA
DAY 3...
AS THE WESTERN TROUGH DROPS DOWN THE NORTHERN CA/NV BORDER ON
MONDAY, SNOW LEVELS ON THE SIERRA NEVADA DROP TO AROUND 7000FT WITH
GENERALLY LIGHT PRECIP. DAY 3 SNOW PROBS FOR >4" ARE AROUND 30% ON
THE HIGH SIERRA AND HIGHEST PARTS OF THE WHITE MTNS.
THE PROBABILITY OF SIGNIFICANT ICE ACROSS THE CONUS DAYS 1-3 IS
LESS THAN TEN PERCENT.
JACKSON
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