Classification of weather types in winter in Thessaloniki during 1989-1999

In the present study a weather type classification is proposed for the winter period in Thessaloniki area. The daily values of several meteorological parameters (absolute, maximum, and minimum temperature, relative and absolute humidity, mean wind velocity, daily precipitation and duration of precipitation, insolation salutation and insolation fraction) were taken from the Meteorological Station of the Aristotle University of Thessaloniki. The data refer to the winter period (December, January, February) of the years from 1989 to 1999. For every month of the study period separately, two combined methods are applied, Principal Component Analysis and Cluster Analysis. Seven weather types for December, six weather types for January, and seven weather types for February emerge.Each month's weather type is compared with weather type of the other two months with the objective, one the one hand their similarities to be identified, and on the other hand their final classification to be defined. Ten new weather types are found, representing the synoptic conditions over the area of Thessaloniki, from December to February during the decade 1989-1999. The new weather types are described, their frequencies are found, and they are compared with the mean circulation.