Flash Flood in Lemhi County, Idaho

A thunderstorm cell developed over extreme southeastern Idaho county (over 9 kft terrain) and split into two separate supercells as it moved into Lemhi County. The left-moving supercell tracked across the old Mustang burn scarred Colson Creek drainage basin (Mustang Fire from 2012). According to Doppler radar estimates, this storm unleashed 0.42 of rainfall in 30 minutes across this drainage basin. At one point the cloud tops reached over 50 kft which meant that the storm had tapped into all the potential instability. These torrential rains produced a debris flow that damaged and made Colson Creek road impassable. The debris flow traveled over several homeowners' properties and damaged a hydro-electric pump causing power outages.

Earlier in the day a surge of monsoon moisture tracked into the region from Nevada allowing for a good buildup of atmospheric moisture. A 40 knot west-southwest, mid-level jet maximum associated with an upper level wave combined with above normal moisture content (precipitable water values near one inch) and strong heating initiated supercell thunderstorms in the early evening hours over western Lemhi County. One particular supercell brought very heavy rains in a short amount of time inducing debris flow over several of the Mustang burn scars. The Mustang fire occurred in the summer of 2012.