Use of percentage of possible sunshine data to prepare automated forecasts of sky cover and to verify plain language forecasts

Abstract

Surveys have indicated a general misunderstanding by the public of many of the sky cover terms used in weather forecasts. This difficulty often carries over to the forecast staff. Reports of hours of bright sunshine were used in the Québec ForecastOffice to attempt to improve the understanding of sky cover terminology. Sunshine data received on a near real-time basis were converted to percent of possible sunshine. A preliminary survey was made in the Québec Forecast Office, followed by a national survey in which all of the other Canadian forecast meteorologists were asked to provide their views on the relationships between sky cover terminology and percentage of possible sunshine. Based on the survey results it was possible to quantify plain language forecasts and consequently to develop techniques to verify them objectively, as well as to prepare computer-produced forecasts. It is proposed that forecasts of hours of bright sunshine or of percent of possible sunshine be used to replace currently misunderstood and often misused terminology. RÉSUMÉ Des sondages ont révélé une incompréhension générale du public concernant plusieurs termes décrivant l'état du ciel utilisés dans les bulletins météorologiques. Cette difficulté est souvent éprouvée aussi par le personnel météorologique. Des messages portant sur l'ensoleillement ont été utilisés par le Centre de prévision du Québec pour tenter d'améliorer la compréhension de la terminologie de l'état du ciel. Les données sur l'ensoleillement, reçues pendant qu'elles étaient encore d'actualité, sont converties enpourcent d'ensoleillement possible. Un sondage préliminaire a eu lieu au Centre de prévision du Québec. Il a été suivi d'un autre sondage mené sur le plan national, auquel tous les prévisionnistes canadiens ont été appelés à exprimer leurs opinions sur la relation existante entre la terminologie de l'état du ciel et le pourcentage d'ensoleillement possible. Sur la base des conclusions des sondages il a été possible de chiffrer le langage des prévisions et par conséquent, dé développer des moyens de vérification par des méthodes objec-*Present affiliation: Canadian Meteorological Centre, Atmospheric Environment Service, Dorval, P.Q. II8/N. Yacowar tives, ainsi que de préparer des prévisions informatisées. Il est recommandé que les prévisions des heures de plein soleil ou du pourcent d'ensoleillement possible soient utilisées pour remplacer une terminologie qui actuelle ment fait défaut sur le plan de la compréhension générale. IntroductionThe present study began in the Québec Forecast Office in the spring of 1977. At that time there was considerable disagreement concerning the meaning of terms used to describe sky cover. Efforts were made to limit the number of such terms. These restrictions were adhered to for a short while but were discontinued when the meteorologists complained they could not adequately present their estimation of the expected sky cover.Natnm (1979) concluded that the benefit of accurate forecasts and timely warnings is lost when those receivi...

Interpretation of Some Terms and Phrases in Public Weather Forecasts

“…The responses from the students and meteorologists concerning the interpretation of cloudiness terms generally are consistent with the results of other studies of the understanding of such terms (e.g., see Abrams, 1980;Riebsame, 1978;Yacowar, 1980). For example, Riebsame (1978) found that terms such as "partly cloudy," "partly sunny," and "fair" are subject to wide ranges of interpretation, and he suggested that numbers (i.e., cloud cover values in percent) as well as phrases be used to describe sky conditions.…”

“…For example, Riebsame (1978) found that terms such as "partly cloudy," "partly sunny," and "fair" are subject to wide ranges of interpretation, and he suggested that numbers (i.e., cloud cover values in percent) as well as phrases be used to describe sky conditions. Yacowar (1980), in a study involving a nationwide survey of meteorologists in Canada, obtained the narrowest ranges of interpretation for the terms "clear," "overcast," and "variable cloudiness" and also reported large regional differences in interpretation of these and other cloudiness terms.…”