Objective and Subjective Precipitation Probability Forecasts: Statistical Analysis of Some Interrelationships

Abstract

This paper addresses two specific questions related to the interrelationships between objective and subjective probability of precipitation (PoP) forecasts: Do the subjective forecasts contain information not included in the objective forecasts? Do the subjective forecasts make full use of the objective forecasts? With respect to the first question, an analysis of more than 11 years of data indicates that the subjective PoP forecasts add information above and beyond that contained in the objective PoP forecasts for all combinations of geographical area, lead time, and season investigated in this study. For longer lead times, this conclusion appears to contradict the results of earlier studies in which the two types of PoP forecasts were compared using aggregate skill scores. With regard to the second question, the statistical results demonstrate that the subjective forecasts generally do not make full use of the objective forecasts. However, these latter results are not as strong, in a statistical sense, as the results related to the first question; moreover, they indicate that it is primarily in the vicinity of the climatological probability (i.e., 0.10 to 0.40) that better use could be made of the objective forecasts. This conclusion suggests that it may be possible to combine the objective and subjective forecasts to produce a PoP forecast with even greater information content.