On the Combination of Forecast Probabilities for Consecutive Precipitation Periods

Abstract

The performance of the method of Hughes and Sangster (1979) for combining precipitation probabilities pertaining to standard 12-h forecast periods is examined for 100 stations in the conterminous United States. Precipitation probabilities for both 24- and 36-h periods are investigated. Although originally derived for a small number of stations by using data from a limited time period, the original formulation is found to be remarkably robust. There is a tendency for overforecasting in the lower half of the probability range, which is most pronounced for the 36-h forecasts. A modification of the original procedure is suggested which largely corrects this problem.