393
FXUS65 KMSO 290659
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
1259 AM MDT TUE SEP 29 2026
DISCUSSION
KEY MESSAGES:
- INCREASING WINDS TODAY, ESPECIALLY ACROSS NORTHWEST MONTANA AND
THE HIGHER TERRAIN.
- SCATTERED RAIN SHOWERS TONIGHT INTO EARLY WEDNESDAY THEN SLIGHT
WARMING TREND INTO THE REMAINDER OF THE WEEK.
- HIGH CONFIDENCE IN WARMER AND DRIER CONDITIONS THIS WEEKEND
THROUGH MUCH OF NEXT WEEK (AND MAYBE BEYOND).
CLOUDS WILL INCREASE ACROSS NORTHWEST MONTANA TODAY AS A
WEAKENING MOISTURE PLUME SETTLES ALONG THE CANADIAN BORDER,
GENERATING LIGHT OROGRAPHIC SHOWERS FOCUSED PRIMARILY OVER HIGHER
TERRAIN. ACROSS THE REST OF THE NORTHERN ROCKIES, EXPECT PARTLY
CLOUDY SKIES AND MILD DAYTIME TEMPERATURES. WESTERLY WINDS WILL
STRENGTHEN LATE THIS MORNING INTO THE AFTERNOON, WITH VALLEY GUSTS
OF 20-30 MPH AND PERSISTENT, STRONGER GUSTS OVER HIGH TERRAIN
LASTING INTO EARLY WEDNESDAY. ON FLATHEAD LAKE, MORNING SOUTHERLY
WINDS OF 15-20 MPH WILL SHIFT SOUTHWESTERLY IN THE AFTERNOON,
WATCH FOR CHOPPY LAKE CONDITIONS.
LIGHT SHOWER ACTIVITY WILL GRADUALLY DRIFT SOUTHWARD, REACHING
THE INTERSTATE 90 CORRIDOR BY WEDNESDAY MORNING. PRECIPITATION
WILL REMAIN PREDOMINANTLY TERRAIN-FORCED, THOUGH ISOLATED LIGHT
SHOWERS MAY SPILL INTO ADJACENT VALLEYS. VALLEY RAINFALL TOTALS
WILL REMAIN MINIMAL (A FEW HUNDREDTHS OF AN INCH AT MOST), WHILE
MOUNTAIN LOCATIONS ACROSS NORTHWEST MONTANA CAN EXPECT 0.10 TO
0.30 INCHES.
BREEZY CONDITIONS WILL RETURN WEDNESDAY AFTERNOON WHILE REMAINING
SHOWERS DIMINISH. A DRIER ZONAL FLOW PATTERN WILL TAKE HOLD LATE
THIS WEEK, SUPPORTING MOSTLY DRY WEATHER AND TEMPERATURES SLIGHTLY
ABOVE SEASONAL NORMALS.
HIGH CONFIDENCE (80-90% ENSEMBLE CLUSTER SUPPORT) EXISTS FOR
STRONG UPPER-LEVEL RIDGING TO BUILD OVER THE NORTHERN ROCKIES THIS
WEEKEND AND PERSIST INTO NEXT WEEK. WHILE 850MB TEMPERATURES
SUPPORT DAYTIME HIGHS 10-20 DEGREES ABOVE SEASONAL AVERAGES,
VALLEY TEMPERATURES MAY BE SLIGHTLY TEMPERED BY AUTUMN VALLEY
INVERSIONS AND LIMITED BOUNDARY-LAYER MIXING. CONVERSELY,
OVERNIGHT VALLEY LOWS ARE EXPECTED TO TREND COOLER THAN BLENDED
GUIDANCE SUCH AS THE NBM SUGGESTS, AS DRY AIR, LIGHT WINDS, AND
CLEAR SKIES FACILITATE EFFICIENT NOCTURNAL RADIATIONAL COOLING.
IT'S INTERESTING TO NOTE THAT MANY ENSEMBLES POINT TOWARD WARMER
AND DRIER THAN NORMAL CONDITIONS CONTINUING THROUGH THE ENTIRE
FIRST HALF OF OCTOBER.
AVIATION
VFR CONDITIONS WILL BE COMMON INTO WEDNESDAY AT TERMINAL SITES.
A WEAKENING MOISTURE PLUME WILL BRING LIGHT SHOWERS TO THE TERRAIN
OF NORTHWEST MONTANA TODAY, GRADUALLY SPREADING TOWARD THE I-90
CORRIDOR BY EARLY WEDNESDAY, CAUSING MOUNTAIN OBSCURATIONS.
WESTERLY WINDS WILL PICK UP LATER THIS MORNING/EARLY AFTERNOON
WITH GUSTS OF 15-25 KTS COMMON FOR VALLEYS. THESE VALLEY GUSTS
WILL DIMINISH AROUND SUNSET BUT CONTINUE OVER THE TERRAIN THROUGH
EARLY WEDNESDAY MORNING.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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