Vol. 122, No. 4 * Pages 361–462 * October - December 2018

DOI:10.28974/idojaras.2018.4.2

This study describes the regularities in spatial and multiannual variations in the occurrence of last spring frost (LSF), first fall frost (FFF) and the length of the frost-free season (FFS). In the paper, daily minimum and maximum air temperatures recorded at 20 stations in Poland in 1951–2015 and a calendar of synoptic situations were used. It was found that at 75% of the analyzed stations the FFS period grew longer and the changes were statistically significant. Clearly, the longer length of the season is attributable to the earlier LSF dates. The frosts under investigation were recorded most frequently in anticyclonic situations, especially in the presence of an anticyclonic wedge (Ka) and a central anticyclone situation (Ca). LSFs and FFFs were predominantly accompanied by arctic (PA), polar maritime old (PPms), and polar continental (PPk) air masses.