592
FXUS65 KMSO 270746
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
146 AM MDT WED AUG 27 2025
DISCUSSION
KEY MESSAGES:
- DEGRADED BUT SLOWLY IMPROVING AIR QUALITY DUE TO WILDFIRE
SMOKE CONTINUES, MAINLY ACROSS CENTRAL IDAHO.
- SOUTHWEST MONSOON MOISTURE TO BRING POTENTIAL FOR FLASH
FLOODING DUE TO HEAVY RAINFALL FROM SLOW-MOVING THUNDERSTORMS
WEDS AND THURS.
DEGRADED AIR QUALITY WILL CONTINUE TO BE AN ISSUE ACROSS WESTERN
MONTANA AND NORTH-CENTRAL IDAHO THROUGH AT LEAST TODAY. LOOKING AT
MONITORING SENSORS THERE HAS BEEN SOME IMPROVEMENT IN NORTH-
CENTRAL ID AND THAT TREND MAY CONTINUE AS PREDOMINANT WINDS CHANGE
SOUTHWESTERLY. AIR QUALITY ALERTS REMAIN IN PLACE UNTIL 11 AM PDT
TODAY AND MAY BE EXTENDED LATER THIS MORNING IF NEED BE.
SOUTHWEST MONSOON MOISTURE HAS SLOWLY BEEN MEANDERING NORTH INTO
OUR REGION AND WILL CONTINUE THAT TREND THROUGH THURSDAY. EVEN
WITHOUT WIDESPREAD THUNDERSTORMS, OBSERVATIONS HAVE DEMONSTRATED
DEEP, WARM PRECIPITATION PROCESSES, WITH 0.40 TO 0.70 PER HOUR
RAINFALL RATES NORTH AND EAST OF BOISE, ID IN THE SAWTOOTH
NATIONAL FOREST. THIS AREA OF PRECIPITATION WILL CONTINUE ITS
NORTHWARD MIGRATION ARRIVING IN LEMHI AND IDAHO COUNTIES MID
MORNING TODAY. THE CLOUD SHIELD ASSOCIATED WITH THIS PRECIPITATION
WILL LIMIT CONVECTION, HOWEVER ON THE PERIFERY OF THE CLOUD
SHIELD CONVECTION WILL BE POSSIBLE. THESE STORMS INITIALLY WILL BE
CAPABLE OF PRODUCING ERRATIC OUTFLOW WINDS 30 TO 40 MPH. ONCE THE
ATMOSPHERE BECOMES MORE SATURATED, HEAVIER SHOWERS WILL BECOME THE
MAIN THREAT.
THIS RAISES THE POTENTIAL FOR ROCK AND DEBRIS FLOWS IN STEEP
TERRAIN, PARTICULARLY ALONG FOREST SERVICE ROADS AND IN AREAS
AFFECTED BY RECENT BURN SCARS.
LOCATIONS WITH THE HIGHEST PROBABILITY FOR RUNOFF ISSUES ARE:
- HIGHWAY 95 FROM RIGGINS TO WHITE BIRD IN IDAHO.
- SKALKAHO AND EAST FORK ROADS IN THE SAPPHIRE RANGE OF MONTANA.
- HIGHWAY 93 SOUTH OF SALMON IDAHO.
CONSIDER POSTPONING ANY BACKCOUNTRY TRAVEL ON WEDNESDAY AND
THURSDAY.
A WEAK SHORTWAVE RIDGE OF HIGH PRESSURE IS EXPECTED TO MOVE OVER
THE NORTHERN ROCKIES THIS WEEKEND. HOWEVER, RESIDUAL MOISTURE WILL
LIKELY REMAIN, SUPPORTING ISOLATED, HIT-OR-MISS SHOWERS AND/OR
THUNDERSTORMS.
AVIATION...SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL
CONTINUE TO SLOWLY SPREAD FROM SOUTH TO NORTH OVER NORTH-CENTRAL
IDAHO AND WESTERN MONTANA THROUGH THURSDAY. LOCATIONS WITH THE
HIGHEST PROBABILITY (25-35%) FOR THUNDERSTORMS, WILL BE KSMN, KBTM
AND KHRF. BRIEF HEAVY RAINFALL AND OCCASIONAL LIGHTNING WILL BE
THE MAIN THREATS. PRECIPITATION WILL BE MORE WIDESPREAD THURSDAY.
MSO WATCHES/WARNINGS/ADVISORIES
MT...FLOOD WATCH FROM NOON MDT TODAY THROUGH THIS EVENING FOR
BITTERROOT/SAPPHIRE MOUNTAINS...MISSOULA/BITTERROOT VALLEYS.
ID...FLOOD WATCH FROM NOON MDT /11 AM PDT/ TODAY THROUGH THIS EVENING
FOR EASTERN LEMHI COUNTY...LOWER HELLS CANYON/SALMON RIVER
REGION...OROFINO/GRANGEVILLE REGION...SOUTHERN CLEARWATER
MOUNTAINS...WESTERN LEMHI COUNTY.
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