Most of the country has a subtropical climate, with cooler temperatures prevailing in the higher altitudes. Winter days are warm and nights are cool, with heavy frost common in the desert. Temperatures range from average maximums of 33° C (91° F ) in January and 22° C (72° F ) in July to average minimums of 18° C (64° F ) in January and 5° C (41° F ) in July. In August begin the seasonal winds that blow from the west and carry sand and dust across the country. Rainfall normally averages 45 cm (18 in) but ranges from 69 cm (27 in) in the north to less than 25 cm (10 in) in the Kalahari; drought conditions prevailed in the early and mid-1980s.