Assessment of Variation of Winter Severity Types in the Siedlce Area

The objective of the work was to describe the thermal and snow conditions in the winter period in the Siedlce area. The average daily air temperatures were used in addition to numbers of days with a snow cover of at least 1 cm for the years 2000–2016 obtained from the Meteorological Station in Siedlce. Dates of the beginning and end of the winter season were determined. The average temperature of the winter season was determined in addition to the degree of winter severity, according to Oskin. The average, minimum and maximum values of parameters were calculated. The probability of an occurrence of individual types of winter severity was determined. Next, principal component analysis and cluster analysis were applied, the latter to the group years in terms of the days with a given type of weather in winter. It was found that – on average – the thermal winter began on 5 December and ended on 6th March. The winter was found to have lasted for 66 days. From year to year, there was observed an increase in the average number of days with mild weather. The greatest decline was found for the days with the weather typical of slightly severe and moderately severe winter. The last study years had the highest average number of days with weather typical of mild, slightly severe and moderately severe winter, and the lowest number of the days with weather typical of severe, very severe, unusually severe and extremely severe winter.