The Sahara's desert climate is believed to have been established over five million years ago during the Pliocene Epoch. Since then the Sahara has been subject to short- to medium-length dry and humid conditions, which have contributed to the unique climate of the Sahara today. For the past 2,000 years, the climate of the Sahara has remained quite consistent, except for a period of time in the 16th and 18th century when there was a "Little Ice Age" in Europe. This ice age significantly increased the amount of precipitation over the whole Sahara Desert until around the 19th century. By this time, the climate had become quite stable again and resembled the desert climate of today.
The Sahara's climate consists of basically two sub-climates, a dry subtropical climate in the north and a dry tropical climate in the south. The dry tropical climate is generally characterized by mild, dry winters, a hot dry season just before the rainy season, and an annual temperature cycle. The dry subtropical climate, however, is characterized by annually high temperature ranges, cold winters, hot summers and two rainy seasons. There is a narrow strip in the western portion of the Sahara, along the coast, which generally has cool temperatures compared to the rest of the Sahara because of the influence of the cold Canary Current.
Dry, subtropical climate
Generally, the dry subtropical climate found in the north is caused by constant high-pressure cells over the tropic of Cancer. The winters are considered cool for desert conditions, with an average temperature of 55° F (13° C). The summers are very hot, with the highest ever recorded temperature at 13° F (58° C). The average rainfall in the subtropical region is approximately 3 inches (76 mm) per year. Precipitation generally falls between December and March, with the maximum rain falling in August and almost no rain at all during May and June. The August storms have been known to cause flash floods which send water to parts of the desert that rarely receive precipitation.
Dry Tropical Climate
The climate of the southern tropical region of the Sahara is dictated by a stable continental air mass and an unstable marine air mass. The average temperature in this region is about 31.5° F (17.5° C), however in the higher elevations, the temperature has been recorded at 5° F (-15° C), which is quite typical. The average annual precipitation is around five inches and includes snow in the higher elevations. In the western part of the tropical region, the cold Canary Current reduces the amount of rainfall, lowers the average temperature, and increases the humidity and the probabality of fog.
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