Change of Hail Frequency

Data on the number of days with hail from 40 meteorological stations for the years 1966–2018 and from the Scientific Station of the Climatology Department of the Jagiellonian University in Krakow for the years 1901–2018 were used in this study. As a result, it was determined that during analysed periods, from April to September, the average number of days with hail ranges from 0.3 to 1.7, and exceed 10 days in mountainous areas. The largest number of days with hail mostly is recorded in the spring months, and also in the autumn by the Baltic Sea. The spatial differentiation of the occurrence of hail in Poland and their annual course largely depend on the impact of local conditions and the meteorological conditions prevailing over a given area (types of atmospheric circulation, air masses and atmospheric fronts). Except for a few stations, no significant changes in long-term variability of the number of days with hail were observed in the period under investigation (1966–2018). Also in Krakow, from 1901 to present day, no significant changes in the number of days with hail have been recorded. However, it is worth paying attention to the significant changes in the number of days examined from year-to-year.