Precipitation Forecasting

Precipitation forecasts from mesoscale numerical weather prediction (NWP) models require a probabilistic forecast approach. This chapter considers forecast lead times as: 0-6 hours, or nowcasting, 3-24 hours, or short term forecasting, and 3-24 months, or seasonal forecasting. Nowcasting is largely based upon the use of radar data; as the lead time increases the forecasts are based upon numerical weather models. An ensemble-based probabilistic precipitation forecasting scheme blends an extrapolation nowcast with a downscaled NWP forecast, and is known as a short term ensemble prediction system (STEPS). An ensemble forecasting system samples the uncertainty inherent in weather prediction to provide more information about possible future weather conditions. Two ensemble forecasting systems are used at the UK Met Office: the Met Office Global and Regional Ensemble Prediction Systems (MOGREPS) are used for short range prediction, and the Medium Range Weather Forecasting (ECMWF) ensemble prediction system is used for the medium range.