WHAT IS A GOOD FORECAST - AN ESSAY ON THE NATURE OF GOODNESS IN WEATHER FORECASTING

Differences of opinion exist among forecasters-and between forecasters and users-regarding the meaning of the phrase ''good (bad) weather fo recasts.'' These differences of opinion are fueled by a lack of clarit y and/or understanding concerning the nature of goodness in weather fo recasting. This lack of clarity and understanding complicates the proc esses of formulating and evaluating weather forecasts and undermines t heir ultimate usefulness. Three distinct types of goodness are identif ied in this paper: 1) the correspondence between forecasters' judgment s and their forecasts (type 1 goodness, or consistency), 2) the corres pondence between the forecasts and the matching observations (type 2 g oodness, or quality), and 3) the incremental economic and/or other ben efits realized by decision makers through the use of the forecasts (ty pe 3 goodness, or value). Each type of goodness is defined and describ ed in some detail. In addition, issues related to the measurement of c onsistency, quality, and value are discussed. Relationships among the three types of goodness are also considered. It is shown by example th at the level of consistency directly impacts the levels of both qualit y and value. Moreover, recent studies of quality/value relationships h ave revealed that these relationships are inherently nonlinear and may not be monotonic unless the multifaceted nature of quality is respect ed. Some implications of these considerations for various practices re lated to operational forecasting are discussed. Changes in these pract ices that could enhance the goodness of weather forecasts in one or mo re respects are identified.