q 2001 American Meteorological Society Microphysics of the Rapid Development of Heavy Convective Precipitation

Two rapidly growing, hail-producing storms observed in Alabama during the Microburst and Severe Thun-derstorm project in 1986 were examined: the well-studied single-cell storm case on 20 July 1986 and a single cell within a multicellular storm on 6 July 1986. Both storms are examples of extremely efficient accretional growth processes that produced hail within 10 min. A simple hydrometeor classification algorithm based on multiparameter radar data was used to identify regions within the rain and snow portions of the storm volumes that included hail, graupel, and supercooled rain. By comparing the results of the simple hydrometeor classification algorithm to previous polarimetric analysis and modeling of the 20 July 1986 storm by other authors, the hydrometeor classification methodology for the 6 July 1986 storm was indirectly validated. The microphysical development of hail and graupel was similar for both the single isolated cell storm and a cell within a multicellular storm. Rapid coalescence within updrafts with high liquid water contents quickly produced precipitation-sized drops that were lofted above the 08C level and subsequently froze. These frozen drops became hail and graupel embryos and continued to grow by accretion. Supercooled rain was present only in the earliest stages of cell evolution lasting 8–12 min and extending 1–2 km above the 08C level. Hail and graupel appeared several minutes after the first appearance of supercooled rain. Graupel was present at highe