An Intense, Quasi-Steady Thunderstorm over Mountainous Terrain. Part I: Evolution of the Storm-Initiating Mesoscale Circulation

Abstract

A detailed, multisensor case study of mesoscale convective storms occurring in summer over the central and eastern Colorado Rockies is presented. This case study uses data obtained during the 1977 South Park Area Cumulus Experiment (SPACE) from surface meteorological stations, rawinsondes and tethered balloons, conventional and Doppler radars, powered aircraft and satellites. On 19 July 1977, a north?south oriented line of intense convective cells formed and remained within South Park, an elevated plain 2.8 km above sea level located within the Rocky Mountains. Elevated surface heating in South Park created a region of low-level convergence which imported Pacific moisture from west of the Rockies into South Park. The mososcale thunderstorm line formed over this convergence zone. Subsequently, northerly surface flow, having the appearance of a ?density current?, penetrated into South Park late in the afternoon, enhancing the intensity of convective storms. Various interactions of the storm system with the mesoscale environment were observed. A single large convective cell was then observed to grow on the southern end of the mesoscale line, exhibiting supercell characteristics and substantial modification of the environmental flow. A detailed description of this quasi-steady storm is given in Parts II and III (Knupp and Cotton, 1982a,b).