An upper level trough moved into the region and interacted with monsoonal moisture to produce thunderstorms.
Every event with a place to put it. Tap one for its entry below.
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.
An upper level trough moved into the region and interacted with monsoonal moisture to produce thunderstorms.
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 4, 1:11 PM MST, 2 hours 54 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MISSOULA MT 211 PM MDT THU AUG 4 2011 .DISCUSSION... AN APPROACHING TROUGH OVER OREGON NOW IS TRIGGERING THUNDERSTORMS ACROSS SOUTHERN AND CENTRAL IDAHO AND INTO EXTREME SOUTHWEST MONTANA. STORMS WILL CONTINUE TONIGHT AND SPREAD INTO WESTERN MONTANA...MAINLY SOUTH OF INTERSTATE 90. THE TROUGH REMAINS ANCHORED OVER THE WEST COAST THROUGH THE WEEKEND...LEAVING THE AREA UNDER SOUTHWEST FLOW. AS A RESULT...THE DAILY PATTERN OF AFTERNOON THUNDERSTORMS AND SHOWERS OVERNIGHT WILL MORE OR LESS CONTINUE THROUGH THE WEEKEND. THE MAIN AREAS AFFECTED WILL CONTINUE TO BE SOUTH OF INTERSTATE 90...AND THE HIGHLINE ALONG THE CONTINENTAL DIVIDE. OTHERWISE...TEMPERATURES REMAIN CLOSE TO SEASONAL AVERAGES UNDER PARTLY CLOUDY SKIES AND LIGHT WINDS. UNSTABLE AFTERNOON CONDITIONS WILL CONTINUE SUNDAY THROUGH THE BEGINNING OF THE WEEK...PROMOTING THE DEVELOPMENT OF AFTERNOON SHOWERS AND POSSIBLY AN ISOLATED THUNDERSTORM. BY MIDWEEK HOWEVER...THE OVERALL GENERAL LONGWAVE PATTERN IS INDICATIVE OF HIGH PRESSURE REBUILDING (ALBEIT RATHER FLATLY) ACROSS THE WESTERN UNITED STATES THROUGH NEXT WEEKEND. THIS WILL ALLOW FOR LITTLE IN THE WAY OF MOISTURE...KEEPING CONDITIONS MOSTLY PRECIPITATION-FREE ACROSS THE NORTHERN ROCKIES. && .AVIATION...ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS WILL CONTINUE TO BUILD THIS AFTERNOON AS AN UPPER LEVEL TROUGH APPROACHES THE NORTHERN ROCKIES. CONVECTION HAS INITIALIZED ACROSS NORTH CENTRAL IDAHO AND SOUTHWEST MONTANA AROUND POTENTIALLY IMPACTING AIRFIELDS KBTM AND KSMN. CONVECTION IS EXPECTED TO SPREAD FURTHER NORTH AFTER 05/0000Z AND COULD REACH TO AIRFIELD KMSO. AREAS NORTH OF A LINE FROM KP69 TO KMSO TO KHLN ARE NOT EXPECTED TO EXPERIENCE WIDESPREAD CONVECTION ALTHOUGH AN ISOLATED THUNDERSTORM IS POSSIBLE. WITH ANY THUNDERSTORMS THAT FORM...THE MAIN THREAT WILL BE FOR GUSTY WINDS AND SMALL HAIL. && NOTE: FLOOD WATCHES...WARNINGS AND ADVISORIES WILL NOT BE LISTED BELOW. .MSO WATCHES/WARNINGS/ADVISORIES... MT...NONE. ID...NONE. && SHORT TERM...LEACH LONG TERM....ALLEGRETTO AVIATION...SMITH
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
426 PM MDT THU AUG 04 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0410 PM TSTM WND DMG 22 S SALMON 44.86N 113.89W
08/04/2011 LEMHI ID TRAINED SPOTTER
A FEW PIECES OF VINYL SIDING, 4FT TO 6FT LONG, BLOWN OFF
HOUSE ALONG WITH SMALL TREES KNOCKED DOWN. WIND GUSTS
ESTIMATED AROUND 50 MPH.
&&
DICKERSONThe Pocatello radar (KSFX), 211 km away, was scanning. The volume nearest the first event began at 23:04 UTC.
1 thunderstorm wind. Local standard time, as filed.
Several pieces of vinyl siding, 4 feet to 6 feet long, were blown off a house. Some small trees were kocked down at the same location.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2011Every state in 2011This day in weather historyWarnings in Idaho, August 2011
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: 334234.