84th AMS Annual Meeting

Thursday, 15 January 2004: 2:45 PM
Bias normalized precipitation scores
Room 6A
Fedor Mesinger, NOAA/NWS/NCEP/EMC and UCAR, Camp Springs, MD; and K. Brill
Poster PDF (2.4 MB)
The purpose of the equitable threat score or various related scores is to provide information on the accuracy of models in placing precipitation above a given threshold. Yet, such scores do not quite manage to achieve this because of their dependence on bias, so that a subjective assessment of how and by how much these scores might have been affected by the model bias is customary. Conversely,common wisdom has it that for improving scores a bias somewhat greater than one is profitable, an enticement toward a practice that can be looked upon as not entirely proper.

It is shown that a more satisfactory state of affairs can be reached. A simple assumption of the increase of hits per unit increase in bias being proportional to the yet unhit area enables calculation of the number of hits normalized to a perfect bias. Thus, normalization of the equitable threat and related scores to perfect bias is possible. Assumption of the odds ratio being independent of bias can be used to the same end. Examples of the resulting bias normalized equitable threat scores of several operational NCEPmodels are presented.

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