The climate of Iran is characterized by large differences in temperature from one season to another and between the north and south of the country. There are three if not four distinct climates in Iran: most regions have the continental climate of long, hot summers and short, sharp winters. In general, winters are cold, except in the Persian Gulf, and summers very hot, with temperatures regularly reaching over 40° C (100° F). Winters in the mountainous regions are harsh and some areas are cut off by snow for weeks on end. In the Iranian province of Azerbaijan and Kurdistan in particular, temperatures fall well below 0° C (32° F) between December and February. In summer, however, these regions are less scorchingly hot than the plateau and the plains, where the temperature climbs steadily from spring onwards to reach between 45° C and 50° C (110°-120° F) in summer, most notably in Khuzestan and the central deserts. Khuzestan, which borders on the Persian Gulf, is also extremely humid and travelling there in summer can be an unpleasant experience. Winters, however, are comfortably warm.
The coastal zone between the Caspian Sea and the Alborz Range has a high rainfall all year round as the mountains form a natural barrier which prevents clouds from moving inland. Temperatures vary between 7° C (45° F) in winter and 26° C (75° F) in summer, sometimes with high humidity. However, the summer heat is less extreme than further south and many popular resorts have sprung up along the coast.
Spring (April to May) and autumn (mid-September to mid-November) are the most pleasant seasons to visit Iran. The inland regions are generally dry then and comfortably warm, although nights are cool. Showers and storms may occur until June in the mountains in the west and in Tehran, and in the northwest, snow often lies in the mountains until April or May.
Visits to the south coast of Iran (eg: Bandar-e Abbas) are best made in the winter months when humidity and heat levels are at their lowest, while spring and autumn are the best times to travel around central and northern Iran. The summer months of June through to early September are best avoided as the temperature can be in the high 40°C, although it is a dry heat except on the south coast.