The subjective process of probability forecasting is analyzed. It is found to contain a sorling aspect, in which the forecaster distributes all instances into an ordered set of categories of likelihood of occurrence, and a laboling aspect, in which the forecaster assigns an anticipated relative frequency, or probability, of occurrence for each category. These two aspects are identified with the concepts of sharpness and validity, which have been introduced by other writers. The verification score proposed by Brier is shown to consist of the sum of measures of these two qualities. A satisfactory measure of synoptic skill is obtained by applying the Brier score to the synoptic probability forecast and to a control forecast of the climatological probability, and by expressing the difference as a percentage of the control score. In an analysis of a large number of short-range probability forecasts made by instructors and students in the synoptic laboratory of the Massachusetts Institute of Technology... Abstract The subjective process of probability forecasting is analyzed. It is found to contain a sorling aspect, in which the forecaster distributes all instances into an ordered set of categories of likelihood of occurrence, and a laboling aspect, in which the forecaster assigns an anticipated relative frequency, or probability, of occurrence for each category. These two aspects are identified with the concepts of sharpness and validity, which have been introduced by other writers. The verification score proposed by Brier is shown to consist of the sum of measures of these two qualities. A satisfactory measure of synoptic skill is obtained by applying the Brier score to the synoptic probability forecast and to a control forecast of the climatological probability, and by expressing the difference as a percentage of the control score. In an analysis of a large number of short-range probability forecasts made by instructors and students in the synoptic laboratory of the Massachusetts Institute of Technology...