12 [No. 98 GEOGRAPHY > (3) CLIMATE The climatic conditions of the Sudan range from Saharan conditions in the north to equatorial condi tions in the extreme south . North of Khartum the Nile valley and desert are practically rainless, though inter mittent winter rains fall on the coast. Khartum itself has an annual mean of 4.76 in . ( 120 mm .); Suakin, on the coast , one of 7.95 in . ( 202 mm . ). South of this region thesummer rains begin , increasing( a) with de crease of latitude and (b) with the proximity of the Abyssinian plateau. The mean at EÌ Obeid is 15 in. (381 mm . ) , at Roseires 28.34 in . ( 720 mm . ) , and at Kassala 12:60 in . ( 320 mm . ). In the extreme south east the climate is of the full equatorial type, with rains lasting from February or March to October or November, and falling with special heaviness in spring and late autumn . Kodok has a mean of 29.76 in. (755 mm. ) and Mongalla of 36.93 in . ( 938 mm . ) .

Since the whole country lies within the tropics , the mean temperature is high . The summers are hottest, winters coldest, and diurnal variations widest in the north . Thus at Berber 120° F. (49° C.) in the shade has been registered in June , whilst in January the ther mometer may fall to 50° F. (10° C. ) . Khartum has a mean maximum (June ) of 107.8° F. ( 42 ° C. ) and a mean minimum ( January ) of 58° F. ( 14.5 ° C. ) . In the highlands of Darfur and in the Upper Nile valley altitude and moisture moderate the heat. The diurnal range, which is considerable , varies from 29.8° F. ( 16° C.) at Wadi Halfa to 22.9° F. ( 12 :5 ° C. ) at Mongalla . North of the twelfth parallel May and June are the hottest months; in the equatorial zone, November and January The north -east trades blow steadily in the interior of the northern Sudan , seldom backing beyond north-west .

At Suakin and Tokar , on the coast , variable winds with violent and often dangerous sand storms prevail be tween June and August. South -west winds are normal