Egypt has a desert climate as a whole: the atmospheric pressure decreases regularly, throughout the year, from N. to S. or from NW. SE., since the Libyan Desert region corresponds to an area of very constant high pressure; nor is much affected by the seasonal movements of the southern cyclonic area, which migrates from Sūdān in the summer months towards the Persian Gulf, thus generating monsoons. These therefore do not reach Egypt where, especially in Upper Egypt, by far the most dominant winds in all seasons are those of N. and NE. (the ages of which Herodotus speaks), which make it possible for sailing ships to go up the Nile thus facilitating trade.
Baric disturbances derive, especially in winter and spring, from cyclonic areas that move on the Mediterranean from W to Egypt, causing precipitation and producing, especially in spring, when these cyclones run more to S. bordering the coast of Marmarica, strong winds of S. (khams ī n) generally very hot (38 ° -41 ° C.) and full of very fine desert dust, whose exhausting effects on the human and animal organism are insufficiently compensated by the advantages brought to certain crops (dates). Just away from the coast, where it is directly influenced by the sea, but above all in Middle and Upper Egypt, the air becomes calm, extremely dry and pure, and thus very suitable for the treatment of rheumatic, pulmonary and heart diseases, waves already Cairo and more Luxor and Aswan are among the most accredited winter climatic resorts. For Egypt 2017, please check mathgeneral.com.
The rains, almost exclusively concentrated in the months of December and January, reach values of 150 to 200 mm. along the Mediterranean coast, where the cultivation of barley is possible thanks to them; but they decrease rapidly on the Delta, and already in Cairo we have an average of 30 mm. in 27 years, the maximum having been 73 mm. and the minimum of 7 mm., while in S. del Fayyüm they are practically nil. This does not mean that, exceptionally, even in Cairo, and even in the desert, torrential rains lasting several hours can be observed, which are harmful to cotton and sometimes cause serious damage not only to the houses of the villages, but also to the cities, without sewers: thus in 1919 certain districts of Cairo were flooded by a violent rain, which in 4 hours reached 43 mm. concentrating in the city also from the next hills.
The temperature, somewhat moderated by the influence of the breezes and by the very proximity of the sea on the Delta and especially in its northern edge, has winter averages of 15 ° (min. + 5 °) in Alexandria; in Cairo the winter average (January) is 13 ° (min. + 20), in spring 25 °, 3 (with absolute maximums of 46 ° during the khams ī n), summer 28 °, 2 (max. 35 °), autumn 18 °, 8. In Upper Egypt the annual average is around 26 °: in winter the temperature fluctuates between 12 ° and 30 ° (min. + 5 °), in summer it rises up to 43 ° in the shade. The daily excursion is very strong, especially in the desert, where the nakedness of the ground facilitates a very intense nocturnal irradiation, so that the torrid heat of the summer afternoon (up to almost 50 °) abruptly occurs cool or even cold nights. As is well known, the phenomenon of the mirage, frequent and intense in Egypt, depends on this extreme warming of the soil, and the intense diffusion actions (spontaneous fracture of the rocks) are linked to it. In winter, the temperature also drops to 4 ° and 5 ° below zero, causing the water in the ponds to freeze and very rarely to frost,
Lightning is not rare; hail, ice, frost are rare as we said, but when they occur they cause serious damage to crops; not infrequent are the mists, especially in autumn, in the low marshy places and on the river. Snow falls on Sinai in winter.
Egypt has a network of 24 weather stations, including a first-rate one in Helwān, which has been in operation since 1904.