074
FXUS65 KMSO 281909
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
109 PM MDT MON SEP 28 2026
DISCUSSION
KEY MESSAGES:
- NEAR-NORMAL TEMPERATURES WITH THE WEATHER PATTERN DURING THIS
WEEK, ALONG WITH MOSTLY DRY CONDITIONS.
- INCREASING WINDS TUESDAY, ESPECIALLY ACROSS NORTHWEST MONTANA AND
THE HIGHER TERRAIN.
- SCATTERED RAIN SHOWERS TUESDAY NIGHT INTO EARLY WEDNESDAY THEN
SLIGHT WARMING TREND INTO THE REMAINDER OF THE WEEK.
- CONFIDENCE INCREASING FOR A WARMER AND DRIER THAN NORMAL EARLY
OCTOBER BEYOND THE 7 DAY FORECAST.
VALLEY INVERSIONS IN SEPTEMBER TODAY STARTED WITH WEAK VALLEY
INVERSIONS WHICH MAY KEEP REALIZATION OF PEAK WARMING SUBDUED
AND HOLD OFF AFTERNOON BREEZES UNTIL LATE AFTERNOON.
TUESDAY AS A WEAK WAVE MOVES THROUGH THE REGION, BREEZY
CONDITIONS ARE EXPECTED TO DEVELOP. STRONGEST WINDS WILL BE NORTH
OF I-90 AND IN THE MOUNTAINS BUT VALLEYS OF NORTHWEST MT COULD
EASILY SEE GUSTS INTO THE 20S ON TUESDAY. DUE TO WINDS DEVELOPING
EARLY LAKE RECREATIONALISTS WILL BE LESS LIKELY TO BE SURPRISED
DURING THE AFTERNOON. THAT SAID, PREPARE FOR CHOPPY CONDITIONS ON
AREA LAKES.
OVERNIGHT INTO WEDNESDAY A FEW SHOWERS DEVELOP, MAINLY ALONG THE
IDAHO/ MONTANA BORDER AND IN GLACIER NATIONAL PARK. THESE SHOWERS
WILL BE LIGHT IN NATURE AND THE PROBABILITY OF A WETTING RAIN, OR
GREATER THAN 1/10 OF AN INCH, IS 40 TO 60% IN THE HIGHEST
TERRAIN. MOST VALLEYS, WITH THE ELEVATED WINDS EVEN OVERNIGHT,
WILL SEE INCREASED EFFECTS OF DOWNSLOPING.
LONGER TERM THE MODELS HAVE BEEN VERY CONSISTENT IS DEMONSTRATING
A BUILDING RIDGE OF HIGH PRESSURE. THIS OUTCOME IS COMMON IN THE
FALL BUT TEMPERATURES IN THE NATIONAL BLEND OF MODELS ARE FORECAST
TO BE 10 TO 15 DEGREES ABOVE NORMAL. THE REASON THIS DISCUSSION
BEGAN WITH 'VALLEY INVERSIONS' IS BECAUSE, DEPENDING IF VALLEY
INVERSIONS DEVELOP AND THEIR STRENGTH, HIGH TEMPERATURE FORECASTS
MAY BE DIFFICULT FOR THE START TO OCTOBER. CURRENT MODELS PREDICT
FOR THE RIDGE AXIS TO BE WEST OF THE ROCKIES, WHICH WOULD ASSIST
IN THE DEVELOPMENT OF VALLEY INVERSIONS. ADDITIONALLY, PACIFIC
TROPICAL ACTIVITY COULD THROW A WRENCH INTO LONGER TERM FORECASTS,
CAUSING MORE VARIATION IN THE PATTERN OR EXCITING RIDGE BREAKDOWNS,
MORE TO COME.
AVIATION
VFR CONDITIONS WILL DOMINATE INTO TUESDAY WITH LIGHT,
DIURNALLY DRIVEN WINDS. WESTERLY WINDS WILL PICK UP ON TUESDAY
LATE MORNING/EARLY AFTERNOON, AND A WEAKENING MOISTURE PLUME WILL
BRING SOME SHOWERS TO THE TERRAIN OF NORTHWEST MONTANA LATE IN THE
DAY.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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