Photographic Documentation of Some Distinctive Cloud Forms Observed Beneath a Large Cumulonimbus

Abstract

Photographs of some variform cloud features observed in the inflow sector of an intense thunderstorm that occurred in southeastern Montana on 11 July 1981 are described. Associated meteorological conditions are interpreted within the context of mesonetwork. aircraft, and radar data collected by the Cooperative Convective Precipitation Experiment (CCOPE). Three transient cloud forms identified as collar, pedestal, and scud (or arcus) clouds occurred within a 30 min period beneath the uniformly flat base of the shelf cloud and near the center of a mesocyclone resolved by multiple-Doppler radial velocity measurements. In contrast to these lowered cloud base anomalies, a cloud-free vault that penetrated upward into the base of the surrounding shelf cloud also is documented. A remarkable bluish coloration in its vertical walls is attributed to backscattering from the celestial dome. All of the departures in cloud base height from the horizontally uniform base of the shelf cloud can be explained in terms of a moisture excess or deficit in various branches of the 3-dimensional circulation around the mesocyclone.