High-resolution WRF-simulated microphysical data during a severe weather event

Cloud microphysical data from several high-resolution simulations of a severe weather event were used to examine the general characteristics of the microphysical schemes currently implemented in the WRF model. The primary purpose of this study was to evaluate the behavior of the microphysical schemes currently implemented in the WRF model. It was shown that each scheme significantly impacted both the domain-averaged mixing ratio profiles and the accumulated surface precipitation. For instance, the two microphysical schemes that consider graupel effects (WSM6 and Lin) produced nearly twice as much precipitation as the simple cloud-water only Ferrier scheme. This indicates that the choice of a microphysical scheme can significantly impact quantitative precipitation forecasts during the warm season. Sensitivity tests with the WSM6 scheme showed that the microphysical mixing ratio profiles are very sensitive to changes in the graupel density and slope intercept parameters. For instance, although a tremendous amount of graupel was generated in the upper troposphere during the small graupel simulation, no graupel extended below 800 hPa. The faster average fall speed of graupel during the large hail simulation, however, greatly reduced (increased) the amount of graupel in the upper (lower) troposphere relative to the small graupel case. Changes in the graupel distribution also significantly impacted the vertical distribution of other microphysical species. The presence of a deep melting layer in the lower troposphere minimized the effect of these changes on the low-level total mixing ratio and the surface precipitation, which suggests that the value of the graupel parameters may be relatively unimportant for precipitation forecasts during the warm season.