An evaluation of the utility of pilot reports (PIREPs) of weather for aviation forecasting product development is presented. Although PIREPs were never intended for quantitative use, this limitation has not prevented developers of improved aviation weather guidance products (such as turbulence or icing forecasting schemes) from using these data. In this paper, an analysis of turbulence reports over the continental United States and Alaska is employed to show that the reports contained within the PIREPs database are inadequate for defining the actual phenomenology of aviation weather hazards. The results suggest that conclusions regarding the frequency of occurrence and intensity of reported aviation weather phenomena contained within PIREPs should not be based on their reported distribution alone because of the effects of operational constraints and various outside influences. The results also suggest that these data are inadequate for developing, calibrating, and validating aviation weather forecasting guidance products. The procedures and regulations for acquiring PIREPs are included in this report, and a discussion is presented suggesting that improvement to the current voice PIREP reporting system might have a wide range of benefits for both the operational and research aviation meteorological communities.
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