Precipitation Characteristics of a Sheared, Moderate Intensity, Supercell-Type Colorado Thunderstorm

Abstract

A dense 450-station network of hail and rain gages in 2025 km2 of northeastern Colorado has provided surface precipitation data from a moderate intensity thunderstorm that crossed the network on 22 July 1972. The storm, which existed in an environmental vertical wind shear of 6 ? 10?2 sec?1 for over 4 hr, exhibited characteristics of the supercell-type storm including a well-defined and continuing weak echo region, a deviate motion to the right of the local winds, a precipitation wall advancing toward the region of strongest inflow, and a forward overhang of high reflectivity as far as 10 km and more ahead of the precipitation wall. The surface precipitation network results from the storm are analyzed and correlated with other measurements obtained from precision radar, instrumented aircraft, multiple high-altitude released dropsondes, rawinsondes, and surface observations. Hail recorded at 12 network stations was associated with two inflow regions that existed simultaneously and moved in divergent directions. Hailfalls correlated with regions of high radar reflectivity gradient. Hailfalls that comprised a principal hailswath were precisely located with respect to the weak echo region of the primary updraft. Four distinct rainfall maxima occurred within the network, each regularly spaced 13 km apart at 15-min intervals. A description of the storm processes is given.