This paper analyses winter severity and snow conditions in the Karkonosze Mountains and Jizera Mountains and examines their long-term trends. The analysis used modified comprehensive winter snowiness (WSW) and winter severity (WOW) indices as defined by Paczos (1982). An attempt was also made to determine the relationship between the WSW and WOW indices. Measurement data were obtained from eight stations operated by the Institute of Meteorology and Water Management -National Research Institute (IMGW-PIB), from eight stations operated by the Czech Hydrological and Meteorological Institute (CHMI) and also from the Meteorological Observatory of the University of Wrocław (UWr) on Mount Szrenica. Essentially, the study covered the period from 1961 to 2015. In some cases, however, the period analysed was shorter due to the limited availability of data, which was conditioned, inter alia, by the period of operation of the station in question, and its type.Viewed on a macroscale, snow conditions in the Karkonosze Mountains and Jizera Mountains (in similar altitude zones) are clearly more favourable on southern slopes than on northern ones. In the study area, negative trends have been observed with respect to both the WSW and WOW indices-winters have become less snowy and warmer. The correlation between the WOW and WSW indices is positive. At stations with northern macroexposure, WOW and WSW show greater correlation than at ones with southern macroexposure. This relationship is the weakest for stations that are situated in the upper ranges (Mount Śnieżka and Mount Szrenica).

Sunshine duration analysis was based on a series of measurements spanning the period from 1901 to 2014 for Śnieżka (1603 m a.s.l.) and from 1961 to 2000 for Szrenica (1362 m a.s.l.). The average annual sunshine duration (SD) on Śnieżka is 1423.0 h, which is among the lowest values in Poland. On average, the main ridge of the Karkonosze range receives 31% of potential sunshine duration in annual terms: from 25% in December to 36% in August and May. The changes in sunshine duration recorded on Śnieżka point to the existence of two cycles: a short one of approx. 2-4 years and a long one of approx. 60 years. The former most probably reflects the rhythm of atmospheric circulation in the North Atlantic (North Atlantic Oscillation), while the latter reflects the impact of ocean circulation associated with the AMO (Atlantic Multidecadal Oscillation) mechanism. Annual SD totals for the years 1901-2014 exhibit a slight trend to an increase of approx. 2.5 h/10 years, and the rate of increase during the winter quarter is many times higher than during the other seasons. Average monthly sunshine duration differences between Śnieżka and Szrenica are positive for all months of the year with the average monthly difference being 10 to 11 h. This means that the average radiation conditions on Śnieżka are more favourable than the main ridge of the Karkonosze range, which lies at an altitude 200 to 250 m lower. Average daily sunshine durations recorded on Śnieżka are only shorter than those on Szrenica for macro-types of atmospheric circulation with advection from the south.