Snow and avalanches

While snowflakes or hail actually fall at the higher altitudes of the Krkonoše Mountains all the year round, continuous snow cover will typically appear in November, reaching a layer of 100 to 300 cm. In the foothills, snow lies on the ground for an average of 70–120 days a year, in the middle ranges 135–160 days and at peak levels more than 180 days. The distribution of snow is primarily determined by wind currents, snow being blown in winter from windward slopes and uppermost surfaces into leeward areas and terrain depressions, so the quality and height of snow is very uneven on the ridges of the mountains. Overhangs and drifts of many metres accumulate within glacial cirque edges and lee sides and determine the development of regular avalanches, the largest snow overhangs occur at the edge of the valleys of Obří důl and Labský důl. Nevertheless, the greatest thickness of accumulated snow, 15 m, was measured on an avalanche path in the valley of Modrý důl (called the Map of the Republic).

Avalanche activity is remarkably intense in the Krkonoše Mountains despite the territory's limited area and low altitude, with over 100 sites (encompassing a total of 554 ha) experiencing avalanche activity on both sides of the range. Visitors to the area should, therefore, respect such places, in particular both slopes of the ridge of Kozí hřbety, the heads of the valleys of Kotelní jámy and Labské jámy, the cirques of Úpská jáma, Śnieżne Kotły, Kocioł Łomniczki and Biały Jar, the latter bearing witness to the greatest avalanche disaster ever in the history of the mountains (20 March 1968, 19 victims).

Although posing a threat to tourism, avalanches represent an irreplaceable natural factor that significantly influences the diversity of the mountains, their paths on the lee sides of glacial cirques largely boasting sites of the greatest diversity in natural history.