The climate in Bhutan varies with altitude, from subtropical in the south to temperate in the highlands and polar-type climate, with year-round snow, in the north. Bhutan experiences five distinct seasons: summer, monsoon, autumn, winter and spring. Western Bhutan has the heavier monsoon rains; southern Bhutan has hot humid summers and cool winters while central and eastern Bhutan is temperate and drier than the west with warm summers and cool winters. The northern region has severe alpine climate and is perpetually under snow. Rainfall can differ within relatively short distances due to rain shadow effects.