The three chief climatic zones are the Saharan, with a wide range of temperatures between day and night; the Sahelian, a semidesert; and the Sudanic, with relatively moderate temperatures. Extreme temperatures range from –12° to 50° C (10°–122° F ); at N'Djamena the average daily maximums and minimums are 42° C (108° F ) and 28° C (73° F ) in April and 33° C (91° F ) and 14° C (57° F ) in December. The rains last from April (in the south) or July (farther north) through October. Average annual rainfall is about 76 cm (30 in) at N'Djamena. In the far south, it is as much as 122 cm (48 in), but at Faya-Largeau in the north, it averages only 2.5 cm (1 in). A severe drought affected two-thirds of the country from 1967 through 1973 and again in the early 1980s, especially 1984.