455
FXUS65 KMSO 121842
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
1242 PM MDT WED AUG 12 2026
DISCUSSION
KEY MESSAGES:
- ISOLATED TO WIDELY SCATTERED STORMS WITH GUSTY OUTFLOWS IN SW
AND WC MT TODAY, WIDESPREAD STORMS ALONG THE CANADIAN BORDER
IN NW MT.
- STRONG EASTERLY GAP WINDS ACCELERATE IN CANYON CORRIDORS
TONIGHT WITH TEMPORARY SURFACE SMOKE RELIEF.
- COOLER, ACTIVE SHOWER/STORM PATTERN CONTINUES THROUGH FRIDAY
BEFORE UPPER RIDGE SLOWLY REBUILDS THIS WEEKEND.
MONSOONAL MOISTURE INTERACTING WITH A MOIST PACIFIC TROUGH
LIFTING ALONG THE CANADIAN BORDER WILL TRIGGER CONVECTION THIS
AFTERNOON AND EVENING. ACROSS SOUTHWEST MONTANA AND AREAS EAST OF
US HIGHWAY 93, ISOLATED TO WIDELY SCATTERED HIGH-BASED
THUNDERSTORMS WILL DEVELOP. DRY SUB-CLOUD LAYERS (INVERTED-V
THERMODYNAMIC PROFILES) WILL FAVOR AN ENVIRONMENT CAPABLE OF MOSTLY
DRY LIGHTNING AND MICROBURST OUTFLOW EXCEEDING 40 MPH. LOCALIZED
HEAVY RAIN WILL BE POSSIBLE MOST CONCERNING IN DEEP CANYONS AND
ACROSS BURN SCARS AND DISTURBED / URBAN GROUND COVER.
IN NORTHWEST MONTANA, SHOWER AND THUNDERSTORM COVERAGE WILL BE
MORE WIDESPREAD PRIMARILY ALONG AND NEAR THE CANADIAN BORDER,
WHERE SYNOPTIC FORCING IS STRONGEST. CONVECTION WILL PERSIST INTO
TONIGHT WHILE STORM COVERAGE WANES AND SLOWLY DRIFTS EASTWARD.
MEANWHILE, A STRENGTHENING LOW-LEVEL EASTERLY PUSH WILL DRIVE A
STRONG NORTHEAST WIND SHIFT THIS EVENING ACROSS NORTHWEST MONTANA,
INCLUDING FLATHEAD LAKE WHERE A LAKE WIND ADVISORY REMAINS IN
EFFECT THROUGH MIDNIGHT. LOW-LEVEL EASTERLY GAP WINDS WILL
ACCELERATE OVERNIGHT THROUGH EAST-TO-WEST TERRAIN PASSES,
PARTICULARLY IN KNOWN-PRONE LOCATIONS SUCH AS BAD ROCK AND
HELLGATE CANYON. THIS EASTERLY FLOW WILL TEMPORARILY CLEAR SURFACE
SMOKE SOUTHWARD, THOUGH ELEVATED SMOKE ALOFT WILL LIKELY REMAIN.
SCATTERED TO WIDESPREAD SHOWER AND THUNDERSTORM COVERAGE WILL
EXPAND WESTWARD ACROSS WESTERN MONTANA AND NORTH-CENTRAL IDAHO ON
THURSDAY AND INTO FRIDAY. ELEVATED PRECIPITABLE WATER (PWAT)
VALUES AND PERSISTENT SYNOPTIC FORCING WILL INCREASE THE POTENTIAL
FOR LOCALIZED HEAVY RAINFALL, PARTICULARLY WITH SLOWER-MOVING
CONVECTIVE CORES. TEMPERATURES WILL REMAIN MODERATED UNDER CLOUD
COVER AND EASTERLY LOW-LEVEL FLOW. NOT EVERY LOCATION WILL MEASURE
NOTABLE NEVERMIND HEAVY PRECIPITATION BUT THE COVERAGE AND
DURATION OF ACTIVE WEATHER IS FAVORABLE FOR MUCH OF WESTERN
MONTANA BEING ABLE TO PULL DOWN SOME LONG-AWAITED RAIN.
THE UPPER-LEVEL RIDGE WILL GRADUALLY REBUILD OVER THE NORTHERN
ROCKIES THIS WEEKEND INTO EARLY NEXT WEEK UNDER SOUTHWESTERLY FLOW
ALOFT. WHILE AFTERNOON TEMPERATURES WILL WARM, MONSOONAL MOISTURE
TAPPED WITHIN THE SOUTHWESTERLY FLOW WILL KEEP PWAT VALUES
ELEVATED. THIS WILL SUSTAIN NEAR-DAILY AFTERNOON SHOWER AND
THUNDERSTORM CHANCES THROUGH THE WEEKEND AND INTO NEXT WEEK,
PREVENTING A RETURN TO COMPLETELY DRY CONDITIONS. WILDFIRE SMOKE
WILL REMAIN A CHALLENGE THROUGH THE LONG-TERM WITH MINIMAL
SUPPRESSION ANTICIPATED AT THIS TIME IN THE SOURCE REGIONS OF THE
SMOKE (WA AND OR).
AVIATION
ISOLATED TO SCATTERED SHOWER AND THUNDERSTORM
ACTIVITY IS EXPECTED TO DEVELOP ACROSS FAR NORTHWEST MONTANA, IN
ADDITION TO LEMHI COUNTY THROUGH SOUTHWEST MONTANA BY MID
AFTERNOON (2-4PM). LIGHTNING CHANCES INCREASE (30% PROBABILITY)
FOR KGPI AND KBTM. WATCH FOR GUSTY OUTFLOW WINDS TO 40 KTS NEAR
ANY THUNDERSTORMS, MAINLY ACROSS SOUTHWEST MONTANA.
ANOTHER WEATHER IMPACT DURING THIS TIME WILL BE SURFACE WIND
SHIFTING TO NORTHEAST FROM NORTH TO SOUTH ACROSS WESTERN MONTANA
THIS EVENING INTO THURSDAY MORNING. 30-40 KNOT WINDS WILL EXIST
OVER THE TERRAIN ALONG THE PORTION OF THE CONTINENTAL DIVIDE JUST
EAST OF KGPI, WITH LESSER WIND SPEEDS FURTHER SOUTH. KGPI AND KMSO
ARE EXPECTED TO SEE GUSTS OF 20-30 KTS.
WILDFIRE SMOKE CONTINUES TO LIMIT VISIBILITY BUT SOME IMPROVEMENT
IS ANTICIPATED BEHIND THE NORTHERLY WIND SHIFT TONIGHT INTO
THURSDAY MORNING.
MSO WATCHES/WARNINGS/ADVISORIES
MT...LAKE WIND ADVISORY FROM 6 PM THIS EVENING TO MIDNIGHT MDT
TONIGHT FOR FLATHEAD/MISSION VALLEYS.
ID...NONE.
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