Estimating Monthly and Seasonal Precipitation Distributions Using the 30- and 90-Day Outlooks

Abstract

A method is presented that specifies gamma distributions consistent with the 30- or 90-day outlook for precipitation and the gamma distribution characterizing the corresponding precipitation climatology. The climatological distribution is progressively adjusted as forecast probabilities depart more strongly from the climatological relative frequency, and in ways that depend on the shape parameter of the climnatological gamma distribution. Parameter maps of the underlying climatological distributions for monthly precipitation totals are provided.