Iran’s climate ranges from arid or semiarid in central and southern parts, to subtropical along the Caspian coast and the northern forests. On the northern edge of the country (the Caspian coastal plain) temperatures rarely fall below freezing and the area remains humid for the rest of the year. Summer temperatures rarely exceed 29 °C (84.2 °F). Annual precipitation is 680 mm (26.8 in) in the eastern part of the plain and more than 1,700 mm (66.9 in) in the western part.
To the west, settlements in the Zagros basin experience lower temperatures, severe winters with below zero average daily temperatures and heavy snowfall. The eastern and central basins are arid, with less than 200 mm (7.9 in) of rain, and have occasional deserts. Average summer temperatures exceed 38 °C (100.4 °F). The coastal plains of the Persian Gulf and Gulf of Oman in southern of Iran have mild winters, and very humid and hot summers. The annual precipitation ranges from 135 to 355 mm (5.3 to 14.0 in).