Throughout Egypt, days are commonly warm or hot, and nights are cool. Egypt has only two seasons: a mild winter from November to April and a hot summer from May to October. The only differences between the seasons are variations in daytime temperatures and changes in prevailing winds. In the coastal regions, temperatures range between an average minimum of 14° C in winter and an average maximum of 30° C in summer.
Temperatures vary widely in the inland desert areas, especially in summer, when they may range from 7° C at night to 43° C during the day. During winter, temperatures in the desert fluctuate less dramatically, but they can be as low as 0° C at night and as high as 18° C during the day.
The average annual temperature increases moving southward from the Delta to the Sudanese border, where temperatures are similar to those of the open deserts to the east and west. In the north, the cooler temperatures of Alexandria during the summer have made the city a popular resort. Throughout the Delta and the northern Nile Valley, there are occasional winter cold spells accompanied by light frost and even snow. At Aswan, in the south, June temperatures can be as low as 10° C at night and as high as 41° C during the day when the sky is clear.
Egypt receives fewer than eighty millimeters of precipitation annually in most areas. Most rain falls along the coast, but even the wettest area, around Alexandria, receives only about 200 millimeters of precipitation per year. Alexandria has relatively high humidity, but seas breezes help keep the moisture down to a comfortable level. Moving southward, the amount of precipitation decreases suddenly. Cairo receives a little more than one centimeter of precipitation each year. The city, however, reports humidity as high as 77 percent during the summer. But during the rest of the year, humidity is low. The areas south of Cairo receive only traces of rainfall. Some areas will go years without rain and then experience sudden downpours that result in flash floods. Sinai receives somewhat more rainfall (about twelve centimeters annually in the north) than the other desert areas, and the region is dotted by numerous wells and oases, which support small population centers that formerly were focal points on trade routes. Water drainage toward the Mediterranean Sea from the main plateau supplies sufficient moisture to permit some agriculture in the coastal area, particularly near Al Arish.
A phenomenon of Egypt's climate is the hot spring wind that blows across the country. The winds, known to Europeans as the sirocco and to Egyptians as the KHAMSIN, usually arrive in April but occasionally occur in March and May. The winds form in small but vigorous low-pressure areas in the Isthmus of Suez and sweep across the northern coast of Africa. Unobstructed by geographical features, the winds reach high velocities and carry great quantities of sand and dust from the deserts. These sandstorms, often accompanied by winds of up to 140 kilometers per hour, can cause temperatures to rise as much as 20° C in two hours. The winds blow intermittently and may continue for days, cause illness in people and animals, harm crops, and occasionally damage houses and infrastructure.