131
FXUS65 KMSO 130828
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
228 AM MDT SUN SEP 13 2026
DISCUSSION
KEY MESSAGES:
- EASTERLY GAP WINDS WILL WEAKEN THROUGH THE MORNING, TURNING
WESTERLY BY THIS AFTERNOON
- WIDESPREAD RAIN AND MOUNTAIN SNOW ABOVE 7,000 FEET LATE
TONIGHT INTO EARLY MONDAY, MAINLY THROUGH CENTRAL IDAHO AND
NORTHWEST MONTANA.
- DRYING AND WARMING CONDITIONS BY MID-WEEK.
A PACIFIC STORM SYSTEM IS MOVING INLAND TODAY AND WILL TRACK INTO
NORTHWEST MONTANA TONIGHT, BRINGING SHOWERS AND ISOLATED
THUNDERSTORMS TO NORTH-CENTRAL IDAHO EARLY THIS MORNING. AHEAD OF
THIS SYSTEM, STRONG EASTERLY WINDS ARE CURRENTLY PEAKING ACROSS
WESTERN MONTANA, PARTICULARLY NEAR THE WHITEFISH, SWAN, AND
MISSION MOUNTAINS, AS WELL AS HELLGATE CANYON. LOCALIZED GUSTS OF
40 TO 50 MPH WILL CREATE CHOPPY LAKE CONDITIONS AND BLUSTERY
BACKCOUNTRY WEATHER BEFORE SHIFTING TO BREEZY WESTERLY WINDS THIS
AFTERNOON.
THE HEAVIEST PRECIPITATION WILL TARGET NORTH-CENTRAL IDAHO AND
NORTHWEST MONTANA, BRINGING UP TO AN INCH OF RAIN IN THE
MOUNTAINS AND LIGHTER AMOUNTS IN THE VALLEYS. SNOW LEVELS WILL
DROP TO NEAR 7,000 FEET TONIGHT, RESULTING IN LIGHT ACCUMULATIONS
ALONG THE CONTINENTAL DIVIDE AND CREATING COLD, RAW CONDITIONS
THAT POSE A HYPOTHERMIA RISK FOR BACKCOUNTRY RECREATIONISTS.
FURTHER SOUTH AND EAST, INCLUDING MISSOULA, RAINFALL WILL BE LIGHT
AND SPOTTY. CONVERSELY, SOUTHWEST MONTANA WILL REMAIN DRY WITH
GUSTY SOUTHWEST WINDS, PROMPTING A RED FLAG WARNING FOR CRITICAL
FIRE WEATHER CONDITIONS THIS AFTERNOON AND EVENING.
THIS WEATHER SYSTEM WILL EXIT THE REGION BY TUESDAY, MAKING WAY
FOR A GENERALLY WARMER AND DRIER PATTERN THROUGH MID-WEEK,
ALTHOUGH A FEW STRAY SHOWERS REMAIN POSSIBLE. DECREASING CLOUD
COVER ON TUESDAY MORNING WILL LIKELY RESULT IN THE COLDEST
TEMPERATURES OF THE FALL SEASON SO FAR. SUB-FREEZING TEMPERATURES
ARE EXPECTED IN THE HIGHER VALLEYS OF SOUTHWEST MONTANA AND ALONG
THE CONTINENTAL DIVIDE, WHILE FROST WILL BE A CONCERN FOR THE
MISSOULA AND BITTERROOT VALLEYS, AS WELL AS THE HIGHER VALLEYS OF
THE CLEARWATER MOUNTAINS. RECENT MODEL TRENDS SUGGEST ANOTHER LOW
PRESSURE SYSTEM MAY CUT OFF ALONG THE WEST COAST WEDNESDAY NIGHT
AND THEN SLOWLY DRIFT THROUGH WESTERN MONTANA AND NORTH CENTRAL
IDAHO THURSDAY INTO FRIDAY. THE MOISTURE FEED WITH THIS SYSTEM
LOOKS RELATIVELY DRY, BUT PRECIPITATION CHANCES MAY TREND UPWARD
AGAIN IN THIS TIME FRAME. THIS SCENARIO APPEARS IN ABOUT 50 TO 60
PERCENT OF MODEL SOLUTIONS, BUT OVERALL CONFIDENCE IN THE DETAILS
REMAINS LOW.
AVIATION
AVIATION OPERATIONS ACROSS WESTERN MONTANA AND NORTH
CENTRAL IDAHO WILL EXPERIENCE DETERIORATING CONDITIONS TODAY INTO
TONIGHT AS A PACIFIC SYSTEM ADVANCES INLAND. THE PRIMARY INITIAL
HAZARD WILL BE STRONG EASTERLY GAP WINDS, WITH LOCALIZED GUSTS OF
40 TO 50 MPH NEAR HELLGATE CANYON AND THE WHITEFISH, SWAN, AND
MISSION MOUNTAINS, GENERATING SIGNIFICANT MECHANICAL TURBULENCE
AND POTENTIAL LOW-LEVEL WIND SHEAR (LLWS) BEFORE SHIFTING TO A
BREEZY WESTERLY FLOW THIS AFTERNOON. CONCURRENTLY, AN AREA OF
SHOWERS AND ISOLATED THUNDERSTORMS PUSHING INTO NORTH-CENTRAL
IDAHO AND NORTHWEST MONTANA WILL RESULT IN WIDESPREAD MOUNTAIN
OBSCURATION AND PERIODS OF MVFR TO LOCALIZED IFR CONDITIONS DUE TO
LOWERED CEILINGS AND REDUCED VISIBILITIES. PRECIPITATION WILL BE
HEAVIEST ACROSS THESE NORTHERN AND WESTERN AREAS, WITH KGPI AND
KGIC SEEING THE MAIN IMPACTS TO CEILINGS FROM RAINFALL.
CONVERSELY, SOUTHWEST MONTANA (KBTM) WILL LARGELY MAINTAIN VFR
CONDITIONS, THOUGH GUSTY SOUTHWESTERLY SURFACE WINDS WILL MAINTAIN
A PERSISTENT THREAT FOR LOW-LEVEL TURBULENCE THROUGHOUT THE
FORECAST PERIOD.
MSO WATCHES/WARNINGS/ADVISORIES
MT...RED FLAG WARNING FROM NOON TODAY TO 9 PM MDT THIS EVENING FOR
EAST BEAVERHEAD.
ID...NONE.
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