A strong low pressure system passing through the Northern Rockies brought periods of heavy rain to north central Idaho. Total precipitation amounts between an inch and an inch and three quarters produced some flash flooding, particularly in the Salmon River Corridor.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS MSO wrote it up.
A strong low pressure system passing through the Northern Rockies brought periods of heavy rain to north central Idaho. Total precipitation amounts between an inch and an inch and three quarters produced some flash flooding, particularly in the Salmon River Corridor.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Missoula, MT wrote its last area forecast discussion before the first event at Aug 31, 1:31 PM MST, 3 hours 59 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MISSOULA MT 231 PM MDT MON AUG 31 2009 .DISCUSSION...TONIGHT THROUGH WEDNESDAY. AN UPPER LOW PRESSURE SYSTEM OVER SOUTHWEST MONTANA WILL SLOWLY SHIFT TO THE EAST OVERNIGHT. HOWEVER...MOISTURE WILL CONTINUE TO BE DIRECTED BACK TO THE WEST ACROSS MAINLY WESTERN MONTANA AND NORTHCENTRAL IDAHO INTO EARLY TONIGHT. CONVECTION HAS BEEN SLOW TO DEVELOP TODAY. HOWEVER...TEMPERATURES SHOULD WARM SUFFICIENTLY TO SUPPORT MORE VIGOROUS CONVECTION BY LATE AFTERNOON. THE BEST COUPLETS OF MOISTURE AND INSTABILITY SHOULD BE FROM THE BITTERROOTS TO THE RATTLESNAKE WILDERNESS AREA AND EASTWARD TO THE DIVIDE. HIGH PRESSURE WILL BEGIN TO BUILD OVER THE REGION TUESDAY. INITIALLY...THIS WILL HELP DRY AND STABILIZE SOUTHWEST MONTANA AND MUCH OF NORTHCENTRAL IDAHO. HOWEVER...SOME MOISTURE AND INSTABILITY WILL TEMPORARILY POOL ACROSS NORTHWEST MONTANA. HIGH PRESSURE SHOULD FURTHER STRENGTHEN WEDNESDAY WITH THE ATMOSPHERE CONTINUING TO DRY AND STABILIZE. THE MAIN IMPACT ASSOCIATED WITH THE BUILDING RIDGE OF HIGH PRESSURE WILL BE QUITE WARM TEMPERATURES WITH VALUES 10 TO 15 DEGREES ABOVE NORMAL BY WEDNESDAY. THURSDAY...FORECAST MODELS CONTINUE TO INDICATE THE UPPER LEVEL RIDGE WILL MOVE EASTWARD ALLOWING SHORTWAVE TROUGHING TO DEVELOP OVER THE NORTHERN ROCKIES. THE BULK OF THE ENERGY AND MOISTURE IS EXPECTED TO MOVE NORTH INTO CANADA...HOWEVER ENOUGH INSTABILITY WILL EXIST AHEAD OF THIS FEATURE TO PRODUCE SOME AFTERNOON THUNDERSTORMS MAINLY ACROSS SOUTHWEST MONTANA. IN ADDITION...A STRENGTHENING SURFACE PRESSURE GRADIENT WILL ALLOW FOR SOME INCREASED SOUTHWEST TO WEST WINDS...ESPECIALLY OVER THE HIGHER TERRAIN. AN UPPER LEVEL TROUGH IS EXPECTED TO FORM OVER THE PACIFIC NORTHWEST THIS WEEKEND...BRINGING SIGNIFICANTLY COOLER AND WETTER CONDITIONS TO THE REGION. TEMPERATURES ARE EXPECTED TO BE AT LEAST 10 TO 15 DEGREES BELOW NORMAL FOR THIS TIME OF YEAR BY SUNDAY...WITH THE POSSIBILITY OF SNOW OVER THE HIGHER MOUNTAIN TERRAIN. LONG RANGE MODELS CONTINUE TO DIFFER SOMEWHAT ON THE STRENGTH OF THIS SYSTEM SO CONFIDENCE ON PRECIPITATION AMOUNTS AND PLACEMENT REMAINS FAIRLY LOW. && .AVIATION...AN UNSTABLE AND RELATIVELY MOIST ATMOSPHERE WILL LINGER...ESPECIALLY ACROSS SOUTHWEST MONTANA THIS EVENING. PARTIAL CLEARING LATER TONIGHT WILL ALLOW SOME FOG AND LOW CLOUDS TO DEVELOP IN THE VALLEYS BY MORNING. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...NONE. ID...NONE. && SHORT TERM...BAUCK LONG TERM....PALLISTER AVIATION...BAUCK
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE MISSOULA MT 319 AM MDT MON AUG 31 2009 IDZ006-009-010-MTZ005>007-312130- SOUTHERN CLEARWATER MOUNTAINS-WESTERN LEMHI COUNTY- EASTERN LEMHI COUNTY-MISSOULA/BITTERROOT VALLEYS- BITTERROOT/SAPPHIRE MOUNTAINS-BUTTE/BLACKFOOT REGION- 319 AM MDT MON AUG 31 2009 /219 AM PDT MON AUG 31 2009/ THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL IDAHO AND WEST CENTRAL MONTANA. .DAY ONE...TODAY AND TONIGHT A LOW PRESSURE SYSTEM WILL CONTINUE TO BRING NUMEROUS SHOWERS AND SCATTERED THUNDERSTORMS TO NORTH CENTRAL IDAHO AND THROUGH SOUTHWEST MONTANA TODAY AND OVERNIGHT. THIS REGION HAS THE POTENTIAL OF RECEIVING SIGNIFICANT PRECIPITATION OVER THE NEXT 24 HOURS. SOME THUNDERSTORMS COULD BECOME STRONG ENOUGH TO PRODUCE SMALL HAIL AND GUSTY WINDS THIS AFTERNOON AND EVENING. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY A COOL AND MOIST WEATHER PATTERN IS EXPECTED FOR THE COMING LABOR DAY WEEKEND. .SPOTTER INFORMATION STATEMENT... WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.
The Missoula radar (KMSX), 186 km away, was scanning. The volume nearest the first event began at 00:28 UTC.
1 flash flood. Local standard time, as filed.
Law enforcement relayed reports of mudslides along the Forth of July Creek Road near milemarker 321 on Highway 93. The combination of mudslides, rocks and boulders made Fourth of July Creek Road impassable.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2009Every state in 2009This day in weather historyWarnings in Idaho, August 2009
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 193382.