680
FXUS65 KMSO 270856
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
256 AM MDT SUN SEP 27 2026
DISCUSSION
KEY MESSAGES:
- NEAR-NORMAL TEMPERATURES THIS UPCOMING WEEK, WITH DRY
CONDITIONS.
- INCREASING WINDS TUESDAY, ESPECIALLY ACROSS NORTHWEST MONTANA
AND THE HIGHER TERRAIN.
- CONFIDENCE INCREASING FOR A WARM, DRY EARLY OCTOBER BEYOND THE
7 DAY FORECAST.
GOES SATELLITE IMAGERY EARLY THIS MORNING SHOWS AN UPPER LEVEL
LOW SPINNING OFF THE SOUTHERN OREGON/NORTHERN CALIFORNIA COAST,
WITH SOUTHWESTERLY FLOW ALOFT BRINGING A SHIELD OF CIRRUS CLOUDS
OVER THE NORTHERN ROCKIES. THIS LOW WILL BEGIN TO SPREAD INLAND
THROUGH THE AFTERNOON, WITH WIDESPREAD CLOUD COVER MOVING
OVERHEAD. MANY LOCATIONS THIS MORNING ACROSS WESTERN MONTANA AND
HIGHER MOUNTAIN VALLEYS OF IDAHO ARE WAKING UP TO FREEZING
TEMPERATURES. STRONG VALLEY INVERSIONS HAVE BEEN OBSERVED AND WITH
CLOUDS MOVING IN, TEMPERATURES WILL BE SLOW TO WARM AS INVERSIONS
ARE SLOW TO BREAK UNTIL EARLY-MID AFTERNOON. SCATTERED SHOWERS
ARE ALSO FORECAST ACROSS LEMHI COUNTY, ID INTO SOUTHWEST MONTANA,
WHERE WEAK SYNOPTIC FORCING WILL PROVIDE SUFFICIENT LIFT FOR
SHOWER DEVELOPMENT. LITTLE TO ANY PRECIPITATION WILL ACCOMPANY
THESE SHOWERS.
A WESTERLY FLOW PATTERN WILL TAKE SHAPE ACROSS THE AREA MONDAY
INTO WEDNESDAY. MODEL GUIDANCE PORTRAYS A SHORTWAVE TROUGH MOVING
ALONG THE USA/CANADA BORDER TUESDAY AFTERNOON THROUGH WEDNESDAY
MORNING. SHOWERS WILL DEVELOP ALONG THE ID/MT BORDER AND ALONG THE
DIVIDE IN NORTHWEST MONTANA AS THIS SYSTEM PUSHES THROUGH.
OVERALL, PRECIPITATION AMOUNTS WILL BE ON THE LOWER SIDE, WITH
ONLY A 40% CHANCE FOR 0.10 INCHES OR MORE OF PRECIPITATION. THIS
SYSTEM WILL BRING AN INCREASE IN WESTERLY WINDS. PEAK GUSTS WILL
REACH 20-25 MPH, LOCALLY TO 30 MPH ACROSS WESTERN MONTANA VALLEYS
AND HIGHER ELEVATIONS OF IDAHO. THE HIGHEST GUSTS WILL IMPACT
MOUNTAIN AREAS ALONG THE DIVIDE IN NORTHWEST MONTANA, INCLUDING
GLACIER PARK, AS WIND GUSTS REACH 30-50 MPH.
HIGH PRESSURE RETURNS THURSDAY INTO FRIDAY, WITH GUIDANCE
SUGGESTING A QUICK HITTING SHORTWAVE TROUGH MOVING ALONG THE
USA/CANADA BORDER ON SATURDAY. ENSEMBLE GUIDANCE HAS BEEN TRENDING
WEAKER WITH THIS TROUGH PASSAGE, WITH ONLY 10% OF THE MEMBERSHIP
SUGGESTING WIDESPREAD PRECIPITATION AND COOLER TEMPERATURES WITH A
COLD FRONTAL PASSAGE ACROSS THE AREA. THE REMAINING 90% OF
GUIDANCE SUGGESTS AN INCREASE IN WINDS, ALONG WITH ISOLATED
SHOWERS ACROSS NORTHWEST MONTANA, WITH MAINLY DRY CONDITIONS AREA
WIDE.
CONFIDENCE 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 3 HURRICANES 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 60-70% 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. 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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