Calibration of probabilistic quantitative precipitation forecasts

From 1 August 1990 to 31 July 1995, the Weather Service Forecast Office in Pittsburgh prepared 6159 probabilistic quantitative precipitation forecasts. Forecasts were made twice a day for 24-h periods beginning at 0000 and 1200 UTC for two river basins. This is the first in a series of articles devoted to a comprehensive verification of these forecasts. The property verified herein is calibration: a match between forecast probabilities and empirical frequencies of events. Monthly time series of calibration statistics are analyzed to infer (i) trends in calibration over time, (ii) the forecasters' skill in quantifying uncertainty, (iii) the adaptability of forecasters' judgments to nonstationarities of the predictand, (iv) the possibility of reducing biases through dynamic recalibration, and (v) the potential for improving calibration through individualized training.