A microphysically based precipitation scheme for the UK Meteorological Office Unified Model

Many numerical weather prediction models are moving towards more prognostic schemes for the prediction of ice and liquid water contents within clouds. This paper describes a large-scale cloud and precipitation scheme develope d for the UK Meteorological Office's Unified Model. It uses physically base d transfer equations to predict ice as a prognostic variable. We review sim ilar schemes and then describe our new scheme, giving examples of its perfo rmance in mesoscale forecasts compared with the current operational scheme and with observations. The microphysical processes occurring in a frontal c loud are well modelled. The prediction of supercooled stratocumulus cloud i s much improved.