The Formation of Stratus in Rain

Sammanfattning: Data analysis of SYNOP observations was made for investigation of stratus formation in rain. The aim was to find connections between meteorological parameters in the different states of rain to develop a forecast method. 1594 cases of rainfall from the four stations Luleå, Uppsala, Linköping and Såtenäs, Sweden were analysed, 974 cases include stratus formation in rain and the other 620 cases are without stratus formation. The investigation focused on the meteorological parameters wind direction, wind speed, relative humidity, visibility, cloud base height and rain intensity. As rain intensity was not explicitly included in the SYNOP observations it could not be taken as a governing parameter, but classification of the data into four groups of different rain intensity was possible. Also time was a parameter for the investigation. The results show that a more detailed investigation should be made to eliminate several influences of other parameters, for example of radiation or soil conditions. Thus it was too difficult to develop a forecast method for the formation of stratus in rain, but suggestions for further investigations and the development of a numerical model only are made.