Strong rising air associated with the nose of a 50 knot mid-level south-southwest jet combined with near record high moisture levels and an unstable atmosphere triggered wet multicellular thunderstorms over Lemhi County by late afternoon on September 5th. Flash flooding and power outages were the main impacts. To get an understanding how moist the air mass associated with this southwest surge was, the Boise weather balloon sounding recorded the 2nd highest moisture level (precipitable water values) on record on the evening of the 5th.

Flash Flood in LEMHI, IDAHO
From 05-SEP-13 17:00:00 to 05-SEP-13 18:00:00 (MST-7)
Location: NORTH FORK
Flood cause: Heavy Rain
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Park/Forest Service

Very wet thunderstorms triggered flash flooding in the Kriley Creek drainage. This debris flow traveled over the northbound lane of highway 93 shutting it down for a period. The BLM road Kriley Gulch Rd was closed in the Kriley Creek drainage due to another separate washout.

Heavy Rain in LEMHI, IDAHO
From 05-SEP-13 16:36:00 to 05-SEP-13 17:36:00 (MST-7)
Location: SALMON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

The Salmon RAWS, located at 5,100 ft. MSL, reported 0.58 of rainfall in one hour. According to radar storm echo trends, the rain could have fallen in less than 30 minutes time.

Heavy Rain in LEMHI, IDAHO
From 05-SEP-13 16:04:00 to 05-SEP-13 17:04:00 (MST-7)
Location: ULYSSES
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

Although not under the main multicellular thunderstorm cores, the Indianola RAWS located at 3,529 ft MSL still reported 0.39 of rain in one hour. Considering what other weather stations in the area reported, this amount could have fallen in a much quicker timescale.

Heavy Rain in LEMHI, IDAHO
From 05-SEP-13 16:51:00 to 05-SEP-13 17:51:00 (MST-7)
Location: NORTH FORK
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

The Kriley Creek RAWS, located at 5,200 ft MSL, reported 0.52 of rain in one hour. Radar data reveals that the rain could have fallen much quicker in approximately 30 minutes or less.

Thunderstorm Wind in LEMHI, IDAHO
From 05-SEP-13 16:36:00 to 05-SEP-13 17:36:00 (MST-7)
Location: SALMON
Magnitude: 60.00 MG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: RAWS

The Salmon RAWS  located 3 miles southwest of the city of Salmon at 5,100 feet reported a strong wind gust to 69 mph that occurred sometime between 5:36 and 6:00 pm MDT. Weather spotters reported trees down and a power outage in Salmon. A television news station reported on Facebook that over 5,000 people were affected. A person from the public in Salmon commented on this post that power was still out in parts of Salmon at 9 am MDT on September 6th.

Flash Flood in LEMHI, IDAHO
From 05-SEP-13 16:30:00 to 05-SEP-13 17:30:00 (MST-7)
Location: SHOUP
Flood cause: Heavy Rain
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Other Federal Agency

A washout near Cramer Creek closed Salmon River Road/NF - 30 for a time. Nearby weather stations in Lemhi county reported anywhere from 0.39 up to 0.58 in less than 30 minutes with these storms.

Thunderstorm Wind in LEMHI, IDAHO
From 05-SEP-13 16:30:00 to 05-SEP-13 17:11:00 (MST-7)
Location: NORTH FORK
Magnitude: 76.00 MG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: RAWS

The Kriley Creek RAWS at 5,200 ft. MSL reported a hurricane force wind gust associated with a wet multicellular thunderstorm. It also reported a 69 mph gust during the 4:51 to 5:51 pm MDT hour. Doppler radar data shows that this gust probably occurred after 5:30 pm MDT. It also showed a wind shift from a west-southwest to a north-northeast direction as the storm passed to the northeast between the 5:51 and 6:51 pm MDT observations. This potentially could be classified as a wet microburst. Power and phone outages were reported in North Fork.