388
FOUS11 KWBC 082017
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
417 PM EDT THU OCT 8 2026
VALID 00Z FRI OCT 09 2026 - 00Z MON OCT 12 2026
..NORTHERN ROCKIES
DAYS 2/3...
TROUGHING WILL SHIFT DOWN THE BRITISH COLUMBIA COAST THROUGH
FRIDAY MORNING BEFORE BEING REINFORCED BY A SHORTWAVE FRIDAY NIGHT,
ALLOWING IT TO DIG AND CLOSE INTO A LOW OVER WASHINGTON/OREGON
SATURDAY BEFORE REACHING NORTHERN CALIFORNIA SUNDAY. LEE-SIDE
CYCLOGENESIS OCCURS OVER SOUTHERN ALBERTA FRIDAY BEFORE SHIFTING
OVER SOUTHERN SASKATCHEWAN/THE DAKOTAS BY SATURDAY. MEANWHILE A
SURFACE RIDGE SHIFTS DOWN THE LEE-SIDE OF THE MONTANA ROCKIES
SATURDAY INTO SUNDAY PROVIDING SOME COLD AIR.
WITH THE TROUGH AXIS SHIFTING DOWN THE WEST COAST, A LONG BUT
SOMEWHAT NARROW MOISTURE PLUME WILL BRING IN PACIFIC MOISTURE TO
THE REGION AS THE COLD FRONT FROM THE NORTH BRINGS IN COLDER SUB-
FREEZING SURFACE TEMPERATURES INTO MONTANA ON SATURDAY.
RAIN WILL TURN TO SNOW IN NORTHWEST MONTANA SATURDAY AS SNOW
LEVELS CRASH FROM 8000FT NEAR PRECIP ONSET TO 3000-4000FT SATURDAY
AFTERNOON AND OVERNIGHT TO SUNDAY. THE COLD AIR REACHES THE WY
BORDER SUNDAY MORNING WITH SNOW LEVELS DIPPING TO 5000-8000FT THERE
THROUGH SUNDAY. SNOW BANDING IS LIKELY, PARTICULARLY OVER WEST-
CENTRAL MONTANA WITH MODERATE TO HEAVY RATES AT TIMES WITH
INCREASING WIND AS NORTHERLY FLOW AT THE SURFACE INTERSECTS THE
TERRAIN JUST NORTH OF A TIGHTENING BAROCLINIC ZONE AS THE FRONT
SLOWS AROUND YELLOWSTONE.
THE REMNANTS OF RACHEL SHOULD QUICKLY TRACK THROUGH THE NORTHERN
ROCKIES SUNDAY NIGHT WITH PRECIP RATES QUICKLY DROPPING OFF MONDAY.
DAY 3 WPC PROBS FOR > 6" ARE 40-70% FOR EASTERN SLOPES OF THE
LEWIS AND FLATHEAD RANGES AND 50-80% FOR THE BIG/LITTLE BELTS, BIG
SNOWY MTNS, AND HIGHER PORTIONS OF THE CRAZY MTNS AND RED LODGE
PORTION OF THE MONTANA ABSAROKAS. THROUGH 12Z SUNDAY ARE >50%
ABOVE ABOUT 5000FT OR SO AND >4" TO ABOUT 4000FT. ACCUMULATING SNOW
SHOULD REACH MOST VALLEY FLOORS OVER WEST-CENTRAL MONTANA THROUGH
THIS PERIOD WITH SOME PROBABILITIES FOR >4" REACHING GREAT FALLS
AND HELENA. THE KEY WILL BE WHERE THE BEST BANDING SETS UP WHICH
WILL OVERCOME THE MARGINAL THERMALS.
THE PROBABILITY OF SIGNIFICANT ICE ACROSS THE CONUS DAYS 1-3 IS
LESS THAN TEN PERCENT.
JACKSON
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