Heavy Rain in Lemhi County, Idaho

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.

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.