A cloud free vault
Weaver, John F., author
A severe squall line, with several isolated storms near its southernmost end, was observed near Grover, Colorado, on the afternoon of 22 July 73 by the NHRE storm monitoring system. The northern segment of the squall line was oriented parallel to cloud level winds (i.e., northeast-southwest), while the southern segment was aligned north-south. The northern segment developed an extensive cloud free vault intruding into the cloud base above the lifting condensation level (LCL) between the precipitation and the updraft pedestal. No downdraft or gust front was observed from the northern segment. Downdrafts and a gust front characterized by a pressure jump of +3 mb and peak winds of 60 knots were produced by both the southern segment and the isolated storms.
National Hail Research Experiment