Recently, the bulk microphysical parameterization in MM5 has been extensively tested, updated, and improved. Sensitivities of the microphysics to primary ice initiation, autoconversion, CCN spectra, treatment of graupel, and parameters controlling the snow and rain size distributions were tested. These tests were performed by simulating various cloud depths (with different cloud-top temperatures) using flow over an idealized two-dimensional mountain. Results were compared against simulations from a detailed, bin microphysical model.

Upon testing the primary sensitivities of the microphysics using idealized flow conditions, the model was used in multiple case studies from various field projects. In this paper, results of the revised scheme are evaluated using data collected during the IMPROVE project. Model-predicted hydrometeor species are compared to observations from radar (SPOL) and multiple aircraft (NOAA-P3 and UW-Convair). Particular emphasis is placed on prediction of freezing drizzle events as well as deep precipitating snowstorms.