Simulation of precipitation fields from probabilistic quantitative precipitation forecast

To assimilate Probabilistic Quantitative Precipitation Forecast (PQPF) into ensemble hydrologic forecasting, a procedure is needed that generates ensemble traces of future precipitation fields from PQPF. This paper describes one such procedure used in the National Weather Serviceʹs (NWS) Ensemble Precipitation Processor (EPP). Given PQPF for the first 24 h valid at the forecast scale (approximately 64×64 km2), the procedure generates ensemble traces of 24- or 6-h precipitation at the simulation scale (approximately 4×4 km2) in space or in space and time, respectively. The steps involved are quasi-analytical downscaling of PQPF and conditional simulation of precipitation fields based on optimal linear estimation techniques that explicitly account for both intermittency and inner variability. To evaluate the procedure, radar-based precipitation data from the Ohio River Forecast Center (OHRFC) are used to develop a climatological PQPF, and to compare ensemble statistics between simulated and observed precipitation.