An Improved Modeling Scheme for Freezing Precipitation Forecasts

Abstract

To improve forecasts of various weather elements (snow, rain, and freezing precipitation) in numerical weather prediction models, a new mixed-phase cloud scheme has been developed. The scheme is based on a single prognostic equation for total water content and includes parameterization of key cloud microphysical processes. The three-dimensional forecasts of solid particles, liquid, and supercooled cloud droplets and different precipitation types are typical outputs of the cloud scheme. It is shown that the scheme compares reasonably well with available meteorological observations. A novel aspect embodied in the scheme is the explicit inclusion of physical processes for the formation of supercooled liquid water. Thus, it is possible to model freezing precipitation and supercooled cloud droplets in the absence of the melting ice mechanism. The inclusion of the supercooled liquid water mechanism increased significantly the probability of detection of freezing precipitation and improved the bias score over the melting ice algorithm alone.