An improved modeling scheme for freezing precipitation forecasts

To improve forecasts of various weather elements (snow, rain, and freezing precipitation) in numerical weather prediction models, a new mixed-phase cl oud scheme has been developed. The scheme is based on a single prognostic e quation 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 compar es reasonably well with available meteorological observations. A novel aspe ct embodied in the scheme is the explicit inclusion of physical processes f or 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 mecha nism increased significantly the probability of detection of freezing preci pitation and improved the bias score over the melting ice algorithm alone.