The Figure presents a schematic of the major features common to each of the flood events. Mid-level steering currents are light and southerly overtop the affected region. A weak shortwave is rotating around the trough and approaching the threat region from the southwest. A surface high centered north of the affected region pushes a cold front southward along the eastern slopes of the mountain range. The post-frontal pressure gradient is locally tighter than nearby pressure gradients and generates a low level ribbon of strong easterly winds oriented nearly perpendicular to the mountain range.
Deep convection develops where the post-frontal easterly ribbon is lifted by the higher terrain.
Individual cells drift northward in the weak southerly steering currents as the slow southward progress of the surface high and its associated post frontal low-level easterly flow focus the convection over the same general area for several hours. The approaching shortwave and upper level divergence maintain favorable deep tropospheric forcing throughout the storm's duration. Radar cross sections show sloping updrafts and a low-echo centroid. Warm cloud processes dominate precipitation production. Moist mid to upper levels, deep warm cloud processes, and cloud bases near the ground severely limit cooling by melting andevaporation thereby minimizing the formation of cool moist downdrafts and propagation of the system away from the mountains.