108
FXUS65 KMSO 291924
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
124 PM MDT TUE SEP 29 2026
DISCUSSION
KEY MESSAGES:
- INCREASING WINDS CONTINUE 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).
SURFACE ANALYSIS AS OF EARLY THIS AFTERNOON INDICATES A BROAD
AREA OF LOW PRESSURE OVER THE GULF OF ALASKA AND AN AREA OF HIGH
PRESSURE OFF THE COAST OF CALIFORNIA. SATELLITE IMAGERY SHOWS
THESE TWO FEATURES FORCING A PLUME OF MOISTURE ONSHORE INTO
WASHINGTON AND SOUTHERN BRITISH COLUMBIA. THE PLUME WILL REACH THE
NORTHERN HALF OF THE NORTHERN ROCKIES THIS EVENING AND OVERNIGHT
TONIGHT. WHILE MOISTURE WILL BE AVAILABLE, FORCING FOR ASCENT WILL
BE SCARCE AS THE UPPER LEVEL JET REMAINS NORTH OF THE BORDER.
PRECIPITATION TONIGHT THROUGH MIDDAY WEDNESDAY 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.
UPPER LEVEL FLOW ON WEDNESDAY BECOMES WEST-NORTHWESTERLY. THE
UPPER LEVEL JET WILL SAG SOUTH OF THE BORDER, BRINGING INCREASING
WEST WINDS TO THE HIGHER TERRAIN OF WESTERN MONTANA INCLUDING THE
IDAHO-MONTANA BORDER.
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
INCREASING CLOUDS AND WIND WILL PERSIST THIS AFTERNOON
AHEAD OF AN INCOMING MOISTURE PLUME. WEST OR SOUTHWEST WINDS
GUSTING 15-25 KNOTS WILL BE COMMON THIS AFTERNOON AND EVENING. THE
INCOMING MOISTURE WILL BRING CHANCES FOR PRECIPITATION TO KGPI
LATE THIS AFTERNOON THROUGH WEDNESDAY MORNING. PRECIPITATION WILL
BE FOCUSED OVER NORTHWEST MONTANA, SO AVIATORS CAN EXPECT
PRECIPITATION TO OBSCURE TERRAIN OVER THE MOUNTAIN RANGES OF
NORTHWEST MONTANA AND THE CLEARWATER RANGE IN IDAHO THIS EVENING
THROUGH ABOUT MIDDAY ON WEDNESDAY.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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