RELIABILITY DIAGRAMS FOR MULTICATEGORY PROBABILISTIC FORECASTS

The most common method of verifying multicategory probabilistic foreca sts such as are used in probabilistic quantitative precipitation forec asting is through the use of the ranked probability score. This single number description of forecast accuracy can never capture the multidi mensional nature of forecast quality and does not inform the forecaste r about the sources of forecast deficiencies. A new type of reliabilit y diagram is developed here and applied to probabilistic quantitative precipitation forecasts from a university contest. This diagram is sho wn to potentially be useful in helping the forecaster to correct some errors in assigning the categorical probabilities.