Une classification des situations météorologiques à l'usage de la prévision

After a critical investigation of the various classifications of meteorological situations proposed up to now, the author chooses the method of HESS and BREZOWSKY, reshaped and adapted to the needs of Swiss forecasters (31 situations have been defined). On the basis of the situation of the day and its probable evolution, the goal is to provide the forecaster with a good estimation of the sunshine, the precipitation quantity and the temperature for the same day and the day after. The second part contains a statistical study, corelating these last three elements with each situation and for the sixteen years 1955 to 1970. For each situation the author states the criteria which characterizes it, its frequency during the year, its average and extreme duration, the most frequent evolutions it undergoes, and the effects it produces on the weather in different parts of Switzerland: sunshine, precipitation, temperature deviations from the mean, cases of foehn. The third and the fourth part contain respectively the day after day classification of all situations from 1955 to 1986 and a topographic index of the situations (on surface and at 500 hPa), together with a short recall of their distinctive features.