The climate of Saudi Arabia varies from one province to another. The Kingdom lies in the tropics, and the nationwide average temperature is 18°C (64°F). Local average vary considerably from 24°C (75°F) in the Western Province, rising as we descend towards the southwest until it reaches 28°C (82°F) in Jeddah and 30°C (86°F) in Jizan. In the northwest, the average temperature is 22°C in Tabouk and 28°C in Madinah, which is 850 meters above the sea level. In the Asir region in the southwest, the average temperature is only 19°C because of the high altitude. The Central Province, which is surrounded by desert, has an average of 25°C for Riyadh, 21°C in Hai'l and 23°C in Qaseem. In Dhahran, the Eastern Province, the temperature is an average of 26°C. Apart from topographical factors, Saudi Arabia's climate is also affected by tropical winds which cause monsoons the west and southwest. These occur during the summer months. In the south, tropical continental winds blow particularly in winter often accompanied by sandstorms.

Saudi Arabia is one of the driest countries in the world, with rainfall averaging less than 5 inches per year.

Source: Saudi Tourism & World Climate

Detailed information on the climate can be found at: Presidency of Meteorology and Environment