Extreme Air Temperatures at the Southwestern Slope of Pirin Mountain (Bulgaria) and Related Synoptic Conditions

Abstract

The article examines the occurrence of extremely cold and extremely warm days as an indicator of environmental changes in the Pirin Mountain (Bulgaria). The study is based on hourly air temperature data recorded by an automatic weather station. By averaging the hourly data, daily values are calculated. The occurrence of extremely cold and extremely warm days during the period 2015–2018 for January, April, July and October are analyzed. Extreme temperature days are determined by threshold values for the 10th and 90th percentiles. Characteristic synoptic situations related to the manifestation of extreme temperatures are presented. As a result of the research it was established that the advections of air masses are the leading factor for the occurrence of extreme temperatures. In addition very important for the extremely low temperatures is the high air pressure over the Balkan Peninsula.