825
FXUS65 KMSO 092009
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
209 PM MDT TUE SEP 9 2025
DISCUSSION
KEY MESSAGES:
- THUNDERSTORMS EACH DAY THROUGH THURSDAY FEATURING GUSTY OUTFLOW
WINDS AND HEAVY RAIN, FOCUSED IN THE AFTERNOON/EVENING HOURS
- TEMPERATURES COOLING THROUGH SATURDAY, RETURNING CLOSER TO
SEASONAL NORMALS
- TURNING WETTER MOST AREAS THURSDAY-SATURDAY, IMPROVING AIR
QUALITY
THE VERY SLOW MOVING UPPER LEVEL LOW PRESSURE SYSTEM OVER NORTHERN
CALIFORNIA WILL BEGIN TO SHIFT NORTHEASTWARDS OVER THE NEXT 72
HOURS. AS IT DOES SO, SPOKES OF MOISTURE AND ENERGY WILL ROTATE
AROUND THE LOW INTO WESTERN MONTANA AND NORTH CENTRAL IDAHO.
SHOWERS AND THUNDERSTORMS WILL BE COMMON THROUGH THURSDAY,
ESPECIALLY FOCUSED IN THE AFTERNOON AND EVENING HOURS. THE MAIN
THREATS WITH STORMS WILL BE GUSTY OUTFLOW WINDS UP TO 40 MPH,
LIGHTNING AND HEAVY RAIN. MEASURABLE RAINFALL WILL NOT BE UNIFORM
ACROSS THE REGION THROUGH THURSDAY DUE TO THE CONVECTIVE NATURE OF
PRECIPITATION. MOST AREAS MAY ONLY SEE A LIGHT SPRINKLE, WHILE
LOCATIONS DIRECTLY UNDER A STORM MAY SEE 0.30 TO 0.75" OF RAIN IN
A SHORT PERIOD OF TIME. FLOOD PRONE AREAS AND RECENT FIRE BURN
SCARS MAY BE PRONE TO DEBRIS FLOWS AND FLASH FLOODING IF THEY TAKE
A DIRECT HIT, BUT OVERALL CONFIDENCE IN THIS OCCURRING IS LESS
THAN 10 PERCENT FOR ANY ONE LOCATIONS.
TEMPERATURES WILL SLOWLY DROP EACH DAY, ESPECIALLY AS CLOUD COVER
AND REGION SMOKE WRAPS INTO THE REGION. BY FRIDAY, TEMPERATURES
WILL HAVE COOLED TO NORMAL, OR SLIGHTLY BELOW NORMAL FOR THIS TIME
OF YEAR (UPPER 60S TO 70S FOR VALLEY LOCATIONS).
SPEAKING OF FRIDAY, FORECAST MODELS ARE TRENDING TOWARDS A WETTER
SOLUTION AS THE LOW PRESSURE SYSTEM EJECTS THROUGH THE REGION.
THERE ARE STILL DIFFERENCES IN THE EXACT TRACK THIS FEATURE WILL
TAKE, BUT THE TREND HAS BEEN TOWARDS MORE WIDESPREAD PRECIPITATION
DEVELOPING, ESPECIALLY THOUGH NORTH CENTRAL IDAHO, AND WEST-
CENTRAL/NORTHWEST MONTANA. THE PROBABILITY FOR A SIGNIFICANT
RAINFALL OF 0.50" OR MORE HAS INCREASED IN THESE AREAS, AND NOW
SITS AT ROUGHLY 50 TO 70 PERCENT IN THE 48 HOURS ENDING SATURDAY
MORNING. AND IN FACT, THE CHANCE OF 1 INCH OF RAIN OR MORE IS NOT
OUT OF THE QUESTION (30 TO 40 PERCENT CHANCE) THROUGH THE TERRAIN
OF NORTH CENTRAL IDAHO AND ALONG THE CONTINENTAL DIVIDE IN
NORTHWEST MONTANA. SOUTHWEST MONTANA AND LEMHI COUNTY MAY MISS OUT
ON THE HEAVIEST PRECIPITATION WITH THIS EVENT. WETTING RAIN LOOK
LIKELY (0.10"+), BUT THE PROBABILITY OF 0.50" OR MORE FALLING FOR
THESE AREAS IS ONLY 15 TO 25 PERCENT.
THE COOLER TEMPERATURES AND INCREASED RAINFALL SHOULD HELP SCRUB
THE AIR CLEAN, MEANING DEGRADED AIR QUALITY FROM WILDFIRE SMOKE
WILL LIKELY IMPROVE. IN ADDITION, WITH THE ANTICIPATED MOISTURE
INCREASE, FOG COULD BECOME MORE OF AN ISSUE ESPECIALLY AS WE
GET MORE CLEARING FRIDAY AND SATURDAY NIGHTS WITH THE LOW
PRESSURE SYSTEM PULLING AWAY.
JUST WHEN YOU THINK WE MIGHT GET A BREAK (SUNDAY) FROM THE
MOISTURE AS THE PREVIOUS SYSTEM EXITS, ANOTHER TROUGH IS FORECAST
TO MOVE ONSHORE BY NEXT MONDAY AND BRING ANOTHER SHOT OF
WIDESPREAD PRECIPITATION!
AVIATION
SHOWERS AND ISOLATED TO SCATTERED THUNDERSTORMS WILL
CONTINUE TO DEVELOP THIS AFTERNOON AND CONTINUE THROUGH MIDNIGHT
TONIGHT ACROSS THE NORTHERN ROCKIES. GUSTY OUTFLOW WINDS TO 35
KTS, SMALL HAIL, HEAVY RAIN, LIGHTNING, AND BRIEF TERRAIN
OBSCURATION WILL BE THE CONCERNS. WATCH FOR PATCHY VALLEY FOG
DEVELOPMENT TONIGHT, ESPECIALLY WHERE RAIN OCCURS TODAY. SHOWERS
AND THUNDERSTORMS ARE EXPECTED AGAIN ON WEDNESDAY.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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