EVALUATION OF 33 YEARS OF QUANTITATIVE PRECIPITATION FORECASTING AT THE NMC

The National Meteorological Center (NMC) initiated Quantitative Precip itation Forecasts (QPF) and an intensive QPF verification program in 1 960. These forecast products have evolved from a manual effort, relyin g on extensive forecast experience to one that placed much greater rel iance on the interpretation and modification of numerical models. Veri fication graphs show steady improvements in forecast accuracy, especia lly for the longer-range forecasts, which in this context are those in the 24-60-h range. During the 1960s the Threat Score (TS) for day-2 f orecasts for 1 in. or more of precipitation averaged approximately 0.0 7. During recent years, that score has nearly doubled, and the 36-60-h period forecast in 1993 had a TS comparable to that for the 12-36-h p eriod during the 1960s. Improvement in accuracy is probably related to a number of diverse factors including improved numerical models, incr eased forecaster knowledge of the strengths and weaknesses of the oper ational models, and an increased understanding of precipitation proces ses. The verification results have been used to track individual and g roup progress.