827
FXUS65 KMSO 271921
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
121 PM MDT SUN SEP 27 2026
DISCUSSION
KEY MESSAGES:
- NEAR-NORMAL WITH THE WEATHER PATTERN DURING UPCOMING WEEK, WITH
DRY CONDITIONS
- INCREASING WINDS TUESDAY, ESPECIALLY ACROSS NORTHWEST MONTANA AND
THE HIGHER TERRAIN.
- A FEW RAIN SHOWERS ON WEDNESDAY THEN WARMING TREND INTO THE
REMAINDER OF THE WEEK.
- CONFIDENCE INCREASING FOR A WARM, DRY EARLY OCTOBER BEYOND THE
7 DAY FORECAST.
SATELLITE IMAGERY SHOWS A VERY LARGE UPPER LOW OVER NORTHERN
CALIFORNIA WHICH IS PUSHING A LOT MOISTURE (IN THE FORM OF THICK
MIDDLE CLOUDS) INTO THE NORTHERN ROCKIES THIS AFTERNOON. THESE
CLOUDS COMBINED WITH THE COLD MORNING THAT WE HAD HAS RESULTED IN
TEMPERATURES CLIMBING SLOWER. HIGH TEMPERATURES COULD BE A FEW
DEGREES COOLER THAN EXPECTED DUE THE CLOUDS TODAY. SHOWERS ARE
SEEN ON THE RADAR EXTENDING FROM LEMHI COUNTY AND POINTS
EASTWARDS. ALSO SHOWERS ARE POISED TO MOVE OVER IDAHO COUNTY.
LATER TODAY, WEAK INSTABILITY COULD RESULT IN A FEW WEAK
THUNDERSTORMS FROM LEMHI COUNTY TO SOUTHWEST MONTANA.
PRECIPITATION MAY STRUGGLE TO MAKE IT TO THE GROUND IN SOME PLACES
DUE TO DRY AIR IN PLACE.
A WEAK SHORTWAVE WILL MOVE ACROSS THE REGION ON MONDAY. THIS WILL
HELP THE SUN TO COME OUT AND PROVIDE WARMING AGAIN. ALSO IT WILL
BRING SOME BREEZY AFTERNOON WESTERLY WINDS, GENERALLY STAYING
BELOW 20 MPH ACROSS NORTHWEST MONTANA.
ON TUESDAY, A WEAKENING MOISTURE PLUME THAT WILL HAVE BROUGHT RAIN
TO SOUTHERN BRITISH COLUMBIA AND NORTHWEST WASHINGTON STATE WILL
BEGIN TO IMPACT NORTHWEST MONTANA. INCREASING CLOUDS, AND WESTERLY
WINDS WILL BE FELT. GENERAL WEST TO SOUTHWEST WINDS OF 10 TO 20
MPH WITH GUSTS TO 30 MPH CAN BE EXPECTED. THERE'S A 50% CHANCE
THAT THE US-2 CORRIDOR BETWEEN HAPPY'S INN AND KALISPELL COULD
EXPERIENCE GUSTS EXCEEDING 30 MPH. OVER THE DIVIDE IN THE GLACIER
REGION, THERE IS A 80% CHANCE FOR WIND GUSTS EXCEEDING 45 MPH. FOR
FLATHEAD LAKE THE PROBABILITIES SUGGEST THAT ONLY A FEW PLACES
COULD EXPERIENCE SUSTAINED 15 MPH WINDS FROM WILD HORSE ISLAND TO
THE CENTER OF THE LAKE, AND ALSO ACROSS SOUTHERN POLSON BAY.
EXPECT CHOPPY CONDITIONS.
THE MAIN MOISTURE PLUME MOVES OVER NORTHWEST MONTANA LATER
TUESDAY NIGHT INTO WEDNESDAY MORNING. EXPECT PERIODS OF LIGHT RAIN
MAINLY IN THE MOUNTAINS. A FEW VALLEY LOCATIONS FROM LOWELL, IDAHO
NORTH AND EAST TO THE SEELEY/SWAN VALLEY, TO GLACIER NATIONAL PARK
HAVE A 40 TO 50% CHANCE OF RECEIVING MEASURABLE MOISTURE IN THE
MORNING.
A GRADUAL WARMING TREND WILL BEGIN TO END THE WEEK!
CONFIDENCE IS INCREASING FOR A WARM, DRY EARLY OCTOBER BEYOND THE
7 DAY FORECAST. THE LARGE SCALE WEATHER PATTERN IS BEING
INFLUENCED BY UPSTREAM TROPICAL ACTIVITY. WITH 2 HURRICANES AND 1
TROPICAL CYCLONE IN THE CENTRAL AND EAST PACIFIC OCEAN FROM HAWAII
TO BAJA AND A TYPHOON APPROACHING THE EASTERN PERIPHERY OF JAPAN,
IT'S BEEN A DIFFICULT FORECAST FOR MODELS. HOWEVER, THEY'RE
STARTING TO COALESCE AROUND HIGHER CHANCES FOR A POTENT RIDGE OVER
THE NORTHERN ROCKIES INTO THE FIRST THIRD OF OCTOBER. ENSEMBLE
MEAN TEMPERATURE FORECASTS ARE COMING IN 15 DEGREES ABOVE SEASONAL
AVERAGES AT ABOUT 9-12 DAYS OUT. THOSE ARE LARGE ANOMALIES FOR
THAT LONG OF A LEAD TIME! ADD IN THAT THE SIGNAL IS COMING FROM
MULTIPLE ENSEMBLE SYSTEMS INCLUDING BOTH DYNAMICAL (PHYSICS BASED)
AND AI MODELING SYSTEMS, THIS PROVIDES ABOVE NORMAL LEVELS OF
CONFIDENCE FOR SUCH A LONG LEAD TIME FORECAST. LOOKING BACK, THE
LAST TIME THIS KIND OF WARM RIDGE SET UP OVER THE NORTHWESTERN US
IN EARLY OCTOBER WAS OCTOBER 9-11 AND 14, 1991. EUREKA, MONTANA
HIT 86 DEGREES, GRANGEVILLE, IDAHO 87 DEGREES, AND BUTTE 81
DEGREES! THE CENTER FOR CLIMATE PREDICTION HAS ISSUED FORECASTS
FOR THE NORTHERN ROCKIES REGION WITH A 70-80% CHANCE OF ABOVE
AVERAGE TEMPERATURES AND PRECIPITATION FORECASTS ARE LEANING BELOW
AVERAGE FOR THAT TIME PERIOD AS WELL.
AVIATION
VFR CONDITIONS ARE EXPECTED ACROSS THE AIRSPACE OVER
THE NEXT 24 HOURS. SATELLITE IMAGERY SHOWS A CLOUD SHIELD MOVING
TOWARDS THE NORTHERN ROCKIES. THIS TREND WILL CONTINUE THROUGH THE
AFTERNOON, WITH CLOUD CEILINGS TRENDING TOWARDS 10,000-15,000
FEET AGL. SCATTERED SHOWERS WILL DEVELOP ACROSS THE HIGHER
TERRAIN OF LEMHI COUNTY, ID INTO SOUTHWEST MONTANA, PERHAPS
LEADING TO ISOLATED TERRAIN OBSCURATIONS OVER THE HIGHEST PEAKS.
PRECIPITATION WILL STRUGGLE TO REACH THE GROUND WITH DRIER AIR IN
THE LOW LEVELS OF THE ATMOSPHERE. WINDS WILL BE PRIMARILY LIGHT
AND TERRAIN-DRIVEN TODAY.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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