Analyses and descriptions of the meteorological conditions that produced devastating flash floods in the Big Thompson Canyon on 31 July 1976 and in the Black Hills on 9 June 1972 are presented. The storms developed when strong low-level easterly winds pushed moist, conditionally unstable air masses upslope into elevated, mountainous terrain. Orographic uplift released the convective instability and light winds aloft allowed the storm complexes to remain nearly stationary. Meteorological conditions that produced these flash floods were found to have been very similar. A set of meteorological features is defined for the purpose of identifying the potential for this type flash flood along the eastern slopes of the Rocky Mountains.