The Hybrid Multicellular–Supercellular Storm—an Efficient Hail Producer. Part II. General Characteristics and Implications for Hail Growth

Abstract

This paper is the second of a two part series describing what are termed hybrid storms because their characteristics are intermediate to classical multicellular and supercellular storms. Storms that possess this structure are worthy of special attention because hail production appears to be enhanced; in fact, they often cause the most severe hailfall events in central Oklahoma. In the first paper, radar reflectivity, internal storm flow and hailstone composition and growth environments of an archetypal hybrid hailstorm are described in detail. Using this and other examples, Part II provides. a more general description. Although these storms are prolific hail producers (maximum hailstone dimensions often >50 mm; hailswath widths and lengths ≥20 and ≥100 km, respectively), seldom are they associated with major tornadic activity. They are also relatively rare with less than one storm per year expected in Oklahoma within an 8100 km2 area. Structurally, they are similar to supercellular storms, but are distinguished by exceptionally large bounded weak echo regions, multiple updraft centers and long pendant rather than hook echoes. An intense and extensive downdraft on the storm's rear flank is believed necessary for formation and maintenance of a hybrid storm. It is suggested that a severe hailfall event is critically dependent on storm kinematical structure rather than microphysical factors. If this is true, then it may be possible to obtain real-time quantitative estimates of hailfall characteristics such as maximum hailstone size and hailswath width through remote sensing of storm flow structure. Speculation is also offered on a dynamical suppression mechanism for hailstorms that tend to the hybrid structure.