734
FXUS65 KMSO 161951
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
1251 PM MST SAT NOV 16 2024
DISCUSSION
KEY MESSAGES:
- HEAVY SNOW TO BRING DIFFICULT WINTER DRIVING CONDITIONS ACROSS
MOUNTAIN PASSES SUNDAY MORNING AND SUNDAY NIGHT.
- SNOW SHOWERS DOWN TO 2,000 FEET BY MONDAY MORNING, WITH MINOR
VALLEY ACCUMULATIONS.
- GROWING CONFIDENCE FOR PROLONGED PRECIPITATION EVENT WEDNESDAY
INTO FRIDAY NEXT WEEK, WITH HIGH ELEVATION SNOW.
GOES SATELLITE IMAGERY THIS AFTERNOON SHOWS A BROAD TROUGH OF LOW
PRESSURE IN THE GULF OF ALASKA, WITH A PLUME OF PACIFIC MOISTURE
STREAMING EASTWARD INTO BRITISH COLUMBIA. THIS TROUGH WILL PIVOT
SOUTHWARD TONIGHT, BRINGING WIDESPREAD PRECIPITATION ACROSS THE
NORTHERN ROCKIES THROUGH MONDAY. SNOW IS EXPECTED TO IMPACT AREAS
ALONG THE ID/MT BORDER TONIGHT, WITH HEAVY SNOWFALL ON I-90 OVER
LOOKOUT PASS, WHERE A WINTER STORM WARNING IS IN EFFECT. SNOWFALL
RATES OF ABOUT 1 INCH PER HOUR WILL CREATE HAZARDOUS TRAVEL
CONDITIONS THROUGH SUNDAY MORNING.
SNOW LEVELS WILL RISE ABOVE 4,500 FEET, ESPECIALLY SOUTH OF I-90,
ON SUNDAY AFTERNOON AS A WARM FRONT MOVES IN. SNOW WILL CONTINUE
TO AFFECT LOOKOUT, LOLO, MARIAS, AND LOST TRAIL PASSES, ALTHOUGH
SNOWFALL INTENSITY WILL DECREASE DUE TO NEAR-FREEZING SURFACE
TEMPERATURES. AS A COLD FRONT MOVES THROUGH SUNDAY NIGHT, SNOW
LEVELS WILL DROP QUICKLY, REACHING 2,000 FEET BY MONDAY MORNING.
WINTER DRIVING CONDITIONS ARE EXPECTED TO DEVELOP ACROSS MOUNTAIN
PASSES, WITH A BURST OF HEAVY SNOW, GUSTY WINDS, AND POOR
VISIBILITY DUE TO BLOWING SNOW. THERE IS MODERATE CONFIDENCE IN
THE POSSIBILITY OF SNOW SQUALLS IMPACTING SOUTHWEST MONTANA,
INCLUDING THE I-90 CORRIDOR NEAR ANACONDA AND BUTTE, AS WELL AS
US-12 OVER MACDONALD PASS AND MONTANA HIGHWAY 1. THESE AREAS COULD
EXPERIENCE FLASH FREEZES, FROM HEAVY SNOW, WIND, AND RAPIDLY
FALLING TEMPERATURES. FUTURE SHIFTS WILL EVALUATE THE NEED FOR
ADDITIONAL WINTER WEATHER ADVISORIES TO ADDRESS THIS THREAT.
SNOW SHOWERS WILL CONTINUE THROUGH MONDAY ABOVE 2,000 FEET.
VALLEY AREAS ALONG US-93, FROM THE FLATHEAD VALLEY THROUGH THE
BITTERROOT, ARE EXPECTED TO SEE ACCUMULATIONS RANGING FROM A TRACE
TO 2 INCHES. MODERATE SNOW WILL CONTINUE TO IMPACT MOUNTAIN
AREAS, INCLUDING LOOKOUT AND LOLO PASSES.
LOOKING AHEAD, MODEL GUIDANCE IS INCREASINGLY POINTING TO AN
ATMOSPHERIC RIVER EVENT FROM WEDNESDAY TO FRIDAY NEXT WEEK. GLOBAL
MODELS SUGGEST A SURFACE LOW WILL UNDERGO STRONG CYCLOGENESIS OFF
THE WASHINGTON COAST ON TUESDAY, DEEPENING TO AROUND 950 MB. THIS
WILL STRENGTHEN A PACIFIC JET, DIRECTING AN ATMOSPHERIC RIVER
INTO THE PACIFIC NORTHWEST AND NORTHERN ROCKIES. WHILE THERE IS
STILL UNCERTAINTY DUE TO THE STRONG CYCLOGENESIS, THE LIKELIHOOD
OF A PROLONGED PRECIPITATION EVENT FOCUSED ON NORTHWEST MONTANA
AND NORTH-CENTRAL IDAHO IS HIGH. SNOW LEVELS REMAIN A KEY
CHALLENGE IN THE FORECAST. THE FLOW DIRECTION REMAINS UNCERTAIN,
WITH MODELS SHOWING A RANGE FROM SOUTHWEST TO WESTERLY WINDS. A
WESTERLY FLOW WOULD LEAD TO LOWER SNOW LEVELS. BASED ON CURRENT
TRENDS, THERE'S A 75% CHANCE FOR SNOW LEVELS ABOVE 4,000 FEET
ACROSS NORTHWEST MONTANA AND ABOVE 5,000 FEET SOUTH OF I-90.
ADDITIONALLY, THERE'S A 25% CHANCE THAT SNOW LEVELS WILL RISE
ABOVE 5,000 FEET IN NORTHWEST MONTANA AND ABOVE 7,000 FEET SOUTH
OF I-90. /AL
AVIATION
WIDESPREAD STRATUS CLOUDS WILL CONTINUE TO BRING
TERRAIN OBSCURATIONS. PACIFIC MOISTURE REMAINS ON TRACK TO BRING
WIDESPREAD PRECIPITATION, WITH SNOW LEVELS DOWN TO 2,500 FEET
TONIGHT INTO SUNDAY MORNING ALONG THE ID/MT BORDER. A SOUTHERLY
GRADIENT WILL INCREASE AFTER 17/0600Z, WITH GUSTY WINDS DEVELOPING
OVER ACROSS THE CAMAS PRAIRIE IN THE VICINITY OF GRANGEVILLE. /AL
MSO WATCHES/WARNINGS/ADVISORIES
MT...WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 11 AM MST
MONDAY FOR KOOTENAI/CABINET REGION...WEST GLACIER REGION.
WINTER WEATHER ADVISORY FROM 5 AM SUNDAY TO 11 AM MST MONDAY FOR
BITTERROOT/SAPPHIRE MOUNTAINS.
WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST SUNDAY
FOR LOWER CLARK FORK REGION.
ID...WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 10 AM PST
MONDAY FOR NORTHERN CLEARWATER MOUNTAINS.
WINTER WEATHER ADVISORY FROM 4 AM SUNDAY TO 10 AM PST MONDAY FOR
SOUTHERN CLEARWATER MOUNTAINS.
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