Doppler-Radar Analysis of a Low-Precipitation Severe Storm

Abstract

This is a detailed study of the structure and evolution of a convective storm that formed along the dryline in Oklahoma on 26 April 1984 and developed into a supercell. Dual-Doppler wind analyses, analyses of surface-mesonetwork and instrumented-tower data, storm-intercept photographs, analyses of raingage data from a dense network, and storm reports are presented and discussed. The storm exhibited the following low-precipitation (LP) characteristics: the absence of any strong, evaporatively cooled, storm-scale downdraft near the surface; a paucity of rain reaching the ground; large hail; long-lived rotating updrafts; and a strong, relatively small in areal extent, unicellular radar echo. The storm split, and its right-moving member developed into an isolated, high-precipitation supercell. It is suggested that the region under cloud base was associated with strong radar echo caused by widely spaced, large water droplets and hailstones. Separate cyclonically and anticyclonically rotating updrafts were found on the southern and northern flanks of the storm, respectively. The high correlation between vorticity and vertical motion is circumstantial evidence that they are dynamically related. The storm split as the updrafts on the northern and southern flanks of the LP storm developed precipitation cores, and each propagated away from the original echo.