Quantitative precipitation forecasting for the Tennessee and Cumberland River watersheds using the NCEP regional spectral model

A limited-area spectral model-the Regional Spectral Model-developed at the National Centers for Environmental Prediction is used to prepare daily quan titative precipitation forecasts out to 48 h for the Tennessee and Cumberla nd River basins in the southeastern United States. One year of these foreca sts is evaluated against data from a network of 243 rain gauges and against traditional man-machine forecasts provided under contract to Tennessee Val ley Authority river system managers. The intent of this study was to determ ine whether the model forecasts, made at greater spatial resolution than th ose typically available from other sources, offered any advantages to water resource managers responsible for making critical day-to-day decisions aff ecting flood control, navigation, and hydropower production. The model's pe rformance, determined using a variety of statistical measures, was found to be more accurate than the traditional forecasts. In particular, the model had less bias and lower root-mean-square error, and was more accurate in th e timing of precipitation events. The model's advantage was especially evid ent in 24-48-h forecasts and for heavy precipitation events. Three specific case studies of model performance are described to illustrate the model's abilities under conditions that could significantly influence river managem ent decisions.