<P> Sand and ground temperatures are even more extreme . During daytime, the sand temperature is extremely high as it can easily reach 80 ° C or 176 ° F or more . A sand temperature of 83.5 ° C (182.3 ° F) has been recorded in Port Sudan . Ground temperatures of 72 ° C or 161.6 ° F have been recorded in the Adrar of Mauritania and a value of 75 ° C (167 ° F) has been measured in Borkou, northern Chad . </P> <P> Due to lack of cloud cover and very low humidity, the desert usually features high diurnal temperature variations between days and nights . However, it is a myth that the nights are cold after extremely hot days in the Sahara . The average diurnal temperature range is typically between 13 and 20 ° C or 23.4 and 36.0 ° F. The lowest values are found along the coastal regions due to high humidity and are often even lower than 10 ° C or 18 ° F, while the highest values are found in inland desert areas where the humidity is the lowest, mainly in the southern Sahara . Still, it is true that winter nights can be cold as it can drop to the freezing point and even below, especially in high - elevation areas . The frequency of subfreezing winter nights in the Sahara is strongly influenced by the North Atlantic Oscillation (NAO), with warmer winter temperatures during negative NAO events and cooler winters with more frosts when the NAO is positive . This is because the weaker clockwise flow around the eastern side of the subtropical anticyclone during negative NAO winters, although too dry to produce more than negligible precipitation, does reduce the flow of dry, cold air from higher latitudes of Eurasia into the Sahara significantly . </P> <P> The average annual rainfall ranges from very low in the northern and southern fringes of the desert to nearly non-existent over the central and the eastern part . The thin northern fringe of the desert receives more winter cloudiness and rainfall due to the arrival of low pressure systems over the Mediterranean Sea along the polar front, although very attenuated by the rain shadow effects of the mountains and the annual average rainfall ranges from 100 millimetres (4 in) to 250 millimetres (10 in). For example, Biskra, Algeria and Ouarzazate, Morocco are found in this zone . The southern fringe of the desert along the border with the Sahel receives summer cloudiness and rainfall due to the arrival of the Intertropical Convergence Zone from the south and the annual average rainfall ranges from 100 millimetres (4 in) to 250 millimetres (10 in). For example, Timbuktu, Mali and Agadez, Niger are found in this zone . The vast central hyper - arid core of the desert is virtually never affected by northerly or southerly atmospheric disturbances and permanently remains under the influence of the strongest anticyclonic weather regime, and the annual average rainfall can drop to less than 1 millimetre (0.04 in). In fact, most of the Sahara receives less than 20 millimetres (0.8 in). Of the 9,000,000 square kilometres (3,500,000 sq mi) of desert land in the Sahara, an area of about 2,800,000 square kilometres (1,100,000 sq mi) (about 31% of the total area) receives an annual average rainfall amount of 10 millimetres (0.4 in) or less, while some 1,500,000 square kilometres (580,000 sq mi) (about 17% of the total area) receives an average of 5 millimetres (0.2 in) or less . The annual average rainfall is virtually zero over a wide area of some 1,000,000 square kilometres (390,000 sq mi) in the eastern Sahara comprising deserts of: Libya, Egypt and Sudan (Tazirbu, Kufra, Dakhla, Kharga, Farafra, Siwa, Asyut, Sohag, Luxor, Aswan, Abu Simbel, Wadi Halfa) where the long - term mean approximates 0.5 millimetres (0.02 in) per year . Rainfall is very unreliable and erratic in the Sahara as it may vary considerably year by year . In full contrast to the negligible annual rainfall amounts, the annual rates of potential evaporation are extraordinarily high, roughly ranging from 2,500 millimetres (100 in) per year to more than 6,000 millimetres (240 in) per year in the whole desert . Nowhere else on Earth has air been found as dry and evaporative as in the Sahara region . However, at least two instances of snowfall have been recorded in Sahara, in February 1979 and December 2016, both in the town of Ain Sefra . </P> <P> The climate of the Sahara has undergone enormous variations between wet and dry over the last few hundred thousand years, believed to be caused by long - term changes in the North African climate cycle that alters the path of the North African Monsoon - usually southward . The cycle is caused by a 41000 - year cycle in which the tilt of the earth changes between 22 ° and 24.5 ° . At present (2000 AD), we are in a dry period, but it is expected that the Sahara will become green again in 15000 years (17000 AD). When the North African monsoon is at its strongest annual precipitation and subsequent vegetation in the Sahara region increase, resulting in conditions commonly referred to as the "green Sahara". For a relatively weak North African monsoon, the opposite is true, with decreased annual precipitation and less vegetation resulting in a phase of the Sahara climate cycle known as the "desert Sahara". </P>

When was the last time it rained in the sahara
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