A comparison study of precipitation forecasts from three numerical weather prediction systems.

摘要

Precipitation forecasts over the Continental US from three numerical weather prediction systems, the 4-km resolution, Storm Scale Ensemble Prediction System (SSEF), the 15-km resolution Global Environmental Multiscale (GEM) model and the 28-km resolution Weather Research and Forecasting (WRF) model, are compared and validated against radar observations for 24 precipitation cases between 16 April and 06 June 2008. The diversity of these systems allows the discussion of several issues: the representation of the diurnal cycle of precipitation in Numerical Weather Prediction (NWP) models, the importance of horizontal resolution for forecast accuracy, the effect of radar data assimilation and the advantage of performing ensemble forecasts rather than less costly, deterministic forecasts. The investigation is carried out through the analysis of statistical measures, skill scores and time-longitude diagrams of precipitation fields.;None of the analysis presented here proved the superiority of the 4-km resolution models over the 15-km resolution GEM. It was however determined that radar data assimilation and ensemble prediction added value to the forecasts, mainly through the reduction of positional errors.;An interesting finding of this study is that, during the study period, the diurnal variability of precipitation was influenced by a combination of weak thermal forcing and strong synoptic forcing, resulting in large scale precipitation systems consistent in terms of initiation timing and propagation characteristics. In addition, the radar observations showed much more consistency than the model forecasts. It is likely that timing and positioning errors led to larger spread of forecasted precipitation coverage and intensity throughout the time-longitude domain.