 At night temperatures regularly drop down to just 4-6 °C (39-43 °F), and morning sunrays regularly have to cut through the dense fog, before they reach the east-facing slopes and provide heat necessary for functioning of this viper.In some north-facing patches, close to the watersheds and summits of mountain ridges, some residual snow and ice never melts.Such patches as a rule are unsuitable for snakes.