Case Study of a Hailstorm in Colorado. Part I: Radar Echo Structure and Evolution

Abstract

A detailed description is given of the morphology and evolution of a moderate hailstorm in terms primarily of quantitative S-band reflectivity factor measurements. During the early phase of the storm's life its movement was strongly influenced by the propagation of new cells on its right flank in a manner typical of ?organized? multicell norms. During its later phase, when it was being intensively observed by research aircraft and Doppler radar, the new cells tended to form on the front flank of the storm in a manner similar to that analysed for the multicellular Raymer storm that has been discussed extensively in the literature. In the present case, however, emphasis is given not to the discrete nature of the cellular propagation, but rather to the quasi-steady overall structure that is comparable in certain ways to previous descriptions of supercell storms, with transient weak-echo vaults and a pronounced forward overhang in the echo structure. The present storm was smaller and less intense than the archetypal supercell, and inferred pulsations in updraft intensity indicate a degree of unsteadiness not generally acknowledged for supercell storms. It is suggested that the present regime represents the extension of a steady airflow pattern to environmental conditions with higher instability or weaker shear.