A better way of using enemble forecasts to generate probability forecasts
•Develop rank histograms based on the precipitation forecast by each of the members.
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•however the shape of the  histograms change significantly based on the variability of the ensemble members. •So separate histograms need to be developed for high, medium and low variability cases.
•How do you handle the heaviest 10%, the extreme rainfall events? 
From Hamill and Colucci, 1998, MWR