486
FXUS65 KMSO 121910
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
110 PM MDT SAT SEP 12 2026
DISCUSSION
KEY MESSAGES:
- EASTERLY GAP WINDS STRENGTHEN TONIGHT INTO SUNDAY MORNING.
ANTICIPATE CHOPPY LAKES AND STRONG CANYON WINDS.
- 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.
SATELLITE IMAGERY EARLY THIS AFTERNOON ACROSS THE NORTHERN ROCKIES
HIGHLIGHTS A CIRRUS CLOUD SHIELD MOVING OVERHEAD UNDER A WESTERLY
FLOW ALOFT. A BROAD LOW PRESSURE SYSTEM IS SEEN OFF THE OREGON
COAST. EASTERLY WINDS OBSERVED EARLIER THIS MORNING ACROSS
WESTERN MONTANA WILL WEAKEN AND SHIFT TO THE WEST-NORTHWEST BY
MID-AFTERNOON INTO THIS EVENING. COOLER TEMPERATURES WILL BE FELT
ACROSS NORTHWEST MONTANA AND ALONG THE DIVIDE TODAY AS THE
EASTERLY GRADIENT THIS MORNING USHERED IN A COLDER AIRMASS THAN
FELT PREVIOUSLY THE LAST FEW DAYS.
LOOKING AHEAD, THE LOW PRESSURE SYSTEM WILL MOVE INLAND TONIGHT
INTO SUNDAY MORNING, TRACKING ACROSS EASTERN WASHINGTON, BEFORE
MOVING ALONG THE USA-CANADIAN BORDER SUNDAY NIGHT INTO EARLY
MONDAY MORNING. EASTERLY WINDS WILL ONCE AGAIN DEVELOP AFTER
SUNSET TONIGHT ACROSS WESTERN MONTANA AND WILL TREND STRONGER THAN
LAST NIGHT. THE STRONGEST GUSTS (30-45 MPH) WILL BE FELT ON
WESTERN SLOPES OF THE WHITEFISH, SWAN, AND MISSION MOUNTAINS AND
IN CANYON/GAP LOCATIONS. THE WINDS WILL GENERALLY PEAK DURING THE
LATE EVENING TO EARLY MORNING HOURS ON SUNDAY AS THE LOW TRACKS
INTO EASTERN WASHINGTON AND THE PRESSURE GRADIENT IS MAXIMIZED.
THOSE PLANNING TO HEAD OUTDOORS SUNDAY MORNING SHOULD BE PREPARED
FOR CHOPPY CONDITIONS ON AREA LAKES AND COOL, BLUSTERY CONDITIONS
IN THE BACKCOUNTRY.
THE LOW PRESSURE'S NORTHERN TRACK CONTINUES TO FOCUS PRECIPITATION
AMOUNTS ACROSS NORTH-CENTRAL IDAHO AND NORTHWEST MONTANA, WHERE
HALF AN INCH TO AROUND AN INCH OF RAIN IS FORECAST ACROSS THE
HIGHER TERRAIN, WITH LESSER AMOUNTS (0.10-0.50 INCHES) IN VALLEY
AREAS. SNOW LEVELS WILL FALL NEAR 7,000 FEET BY SUNDAY NIGHT IN
THESE AREAS. BACKCOUNTRY RECREATIONISTS SHOULD PREPARE FOR COLD,
WET, AND RAW CONDITIONS THAT WILL SIGNIFICANTLY INCREASE THE RISK
OF HYPOTHERMIA FOR ANYONE CAUGHT UNPREPARED. FURTHER SOUTH AND
EAST, INCLUDING THE MISSOULA AREA, PRECIPITATION AMOUNTS WILL BE
NOTABLY LESS (< 0.10 INCHES). SOUTHWEST MONTANA, EAST OF THE
DIVIDE (EAST AND SOUTH OF I-15 AND I-90), WILL REMAIN DRY WITH
GUSTY SOUTHWEST WINDS, RESULTING IN CRITICAL FIRE WEATHER, WHERE A
RED FLAG WARNING IS IN PLACE FOR SUNDAY AFTERNOON AND EVENING.
THE SYSTEM WILL DEPART TO THE EAST BY TUESDAY, TRANSITIONING THE
REGION TO A GENERALLY WARMER AND DRIER WEATHER PATTERN THROUGH
MID-WEEK. DESPITE THE OVERALL DRYING TREND, A FEW WEAK ATMOSPHERIC
DISTURBANCES MAY STILL TRIGGER ISOLATED, LIGHT SHOWERS. TUESDAY
MORNING STANDS OUT AS HAVING THE POTENTIAL TO BE ONE OF THE
COLDEST MORNINGS YET THIS FALL. THE HIGHER VALLEYS OF SOUTHWEST
MONTANA AND AREAS ALONG THE CONTINENTAL DIVIDE WILL SEE LOW
TEMPERATURES NEAR OR BELOW FREEZING. FROST IS ALSO A POTENTIAL
CONCERN FOR THE MISSOULA AND BITTERROOT VALLEY AND HIGHER MOUNTAIN
VALLEYS WITHIN THE CLEARWATER MOUNTAINS OF IDAHO.
AVIATION
VFR CONDITIONS WILL CONTINUE THROUGH THIS EVENING
ACROSS WESTERN MONTANA AND NORTH CENTRAL IDAHO AHEAD OF AN
APPROACHING LOW-PRESSURE SYSTEM. AVIATION OPERATIONS WILL BE
IMPACTED BY INCREASING EASTERLY WINDS, AS WINDS DEVELOP THIS
EVENING (13/0100-0300Z), AND PEAK TONIGHT INTO EARLY SUNDAY
MORNING. GUSTS OF 30-45 MPH WILL DEVELOP NEAR FAVORED CANYONS AND
WESTERN FACING SLOPES, LIKELY INDUCING LOCALIZED MECHANICAL
TURBULENCE AND AREAS OF LOW-LEVEL WIND SHEAR. FLIGHT CONDITIONS
ARE EXPECTED TO DETERIORATE LATE TONIGHT THROUGH SUNDAY AS
WIDESPREAD SHOWERS AND ISOLATED THUNDERSTORMS OVERSPREAD THE
AIRSPACE. THIS INCOMING SYSTEM WILL LEAD TO WIDESPREAD MOUNTAIN
OBSCURATIONS AND PERIODS OF MVFR TO LOCALLY IFR CEILINGS AND
VISIBILITIES, WITH THE MOST SIGNIFICANT FLIGHT IMPACTS
CONCENTRATED OVER NORTH-CENTRAL IDAHO AND NORTHWEST MONTANA WHERE
THE HEAVIEST PRECIPITATION IS FORECAST.
MSO WATCHES/WARNINGS/ADVISORIES
MT...RED FLAG WARNING FROM NOON TO 9 PM MDT SUNDAY FOR EAST
BEAVERHEAD.
ID...NONE.
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