686
FXUS65 KMSO 171221
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
521 AM MST SUN NOV 17 2024
UPDATE
ISSUED A WINTER WEATHER ADVISORY FOR THE SEELEY/SWAN
REGION, THAT IS IN EFFECT UNTIL 11AM THIS MORNING. SNOW-COVERED
ROADS ARE EXPECTED DURING THIS TIME.
PREV DISCUSSION
/ISSUED 206 AM MST SUN NOV 17 2024/
DISCUSSION...
KEY MESSAGES:
- HEAVY SNOW TO BRING DIFFICULT WINTER DRIVING CONDITIONS ACROSS
MOUNTAIN PASSES THIS MORNING AND AGAIN TONIGHT.
- 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.
MODERATE TO HEAVY SNOW IS NOW OCCURRING OVER MOUNTAIN PASSES
ALONG THE ID/MT BORDER, SPECIFICALLY OVER LOOKOUT PASS WHERE 1"/HR
RATES BEGAN AFTER MIDNIGHT THIS MORNING. THE HEAVY SNOW RATES
WILL CONTINUE INTO THE EARLY AFTERNOON. LIGHT TO MODERATE SNOWFALL
HAS BEEN REPORTED IN THE VALLEYS OF NORTHWEST MONTANA FROM LIBBY
TO KALISPELL, THOUGH ONLY MINOR IMPACTS TO ROADS ARE EXPECTED, AS
TEMPERATURES WILL BE WARMING TO ABOVE FREEZING SHORTLY AFTER
SUNRISE. HOWEVER, SCATTERED SLICK SPOTS CAN BE EXPECTED FOR ANYONE
ON THE ROADS AROUND SUNRISE.
SNOW LEVELS WILL RISE ABOVE 4,500 FEET, ESPECIALLY SOUTH OF I-90,
BY THIS AFTERNOON AS A WARM FRONT MOVES IN. SNOW WILL CONTINUE TO
AFFECT LOOKOUT, LOLO, MARIAS, AND LOST TRAIL PASSES, ALTHOUGH
SNOWFALL INTENSITY WILL DECREASE. AS A COLD FRONT MOVES THROUGH
TONIGHT, SNOW LEVELS WILL DROP QUICKLY, REACHING 2,000 FEET BY
MONDAY MORNING. WINTER DRIVING CONDITIONS ARE EXPECTED TO RETURN
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.
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. THERE IS A MODERATE CONFIDENCE THAT A FEW SNOWBANDS
COULD DEVELOP, ALLOWING FOR ISOLATED AREAS SEEING SLIGHTLY HIGHER
ACCUMULATIONS. 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. 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. CURRENT TRENDS IN THE NATIONAL BLEND OF MODELS, HAVE SNOW
LEVELS HIGHER THAN PREVIOUS RUNS. THERE IS NOW A 80-90%
PROBABILITY FOR SNOW LEVELS ABOVE 5,000 FEET SOUTH OF I-90 AND A
50% PROBABILITY FOR NORTHWEST MONTANA. ADDITIONALLY, THERE'S A 30%
PROBABILITY THAT SNOW LEVELS WILL RISE ABOVE 7,000 FEET IN
NORTHWEST MONTANA AND 60% 7,000 FEET SOUTH OF I-90.
CURRENTLY, APPROXIMATELY 60% OF ENSEMBLE FORECAST MODELS ARE
SHOWING A COLDER TROUGH OF LOW PRESSURE ARRIVING TO THE NORTHERN
ROCKIES SOMETIME AROUND THE THANKSGIVING HOLIDAY. THIS WILL BE
WATCHED CLOSELY, SO STAY TUNED.
AVIATION...MODERATE TO HEAVY MOUNTAIN SNOWFALL IS OCCURRING
ACROSS THE NORTHERN ROCKIES THIS MORNING AND WILL CONTINUE INTO
THE AFTERNOON HOURS. LIGHT SNOW IS ALSO FALLING IN THE AREA OF
KGPI THIS MORNING, BUT WARMING TEMPERATURES AFTER SUNRISE TO ABOVE
FREEZING WILL LIMIT ANY GROUND IMPACTS, TO LOWER CEILINGS AND
VISIBILITY. A STRONG COLD FRONT WILL MOVE THROUGH THE AREA LATER
THIS EVENING, THAT WILL BRING A RETURN TO HEAVY MOUNTAIN SNOW,
ALONG WITH GUSTY SOUTHWEST WINDS. CURRENTLY, THERE IS A 60%
PROBABILITY THAT 1"/HR SNOW RATES COULD OCCUR FOR KBTM AS THE
FRONT MOVES THROUGH BETWEEN 18/0500Z-0900Z.
MSO WATCHES/WARNINGS/ADVISORIES
MT...WINTER WEATHER ADVISORY UNTIL 11 AM MST MONDAY FOR
BITTERROOT/SAPPHIRE MOUNTAINS...KOOTENAI/CABINET REGION...
WEST GLACIER REGION.
WINTER STORM WARNING UNTIL 11 AM MST MONDAY FOR LOWER CLARK FORK
REGION.
WINTER WEATHER ADVISORY UNTIL 11 AM MST THIS MORNING FOR
POTOMAC/SEELEY LAKE REGION.
ID...WINTER WEATHER ADVISORY UNTIL 10 AM PST MONDAY FOR NORTHERN
CLEARWATER MOUNTAINS...SOUTHERN CLEARWATER MOUNTAINS.
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