Sensitivity of precipitation forecasts to microphysical parameterization and grid-resolution at convective-allowing and cloud-allowing scales

Description

Twelve precipitation forecasts were compared during the 2010–11 winter rainy season over Israel using two versions of WRF: (a) with Single Moment Scheme (WSM6) bulk-parameterization and (b) with spectral bin microphysics (SBM). Forecasts were performed using 1.3-km and 4-km grid spacing. The results from 12 forecast cases showed no clear forecast improvement with decrease in grid spacing when WSM6 was used. The results show that the SBM forecasts were ranked higher than the forecasts using WSM6 at 1.3- or 4-km grid spacing, deterministic or ensemble. They were also better than forecasts obtained with other bulk microphysical schemes, when compared against station data at the Hermon Mountains for a single test case. This study suggests that the utilization of cloud-resolving scales (1.3 km) in forecast models should be accompanied by improvement in the microphysical description of cloud processes to realize the benefit of high resolution.