シベリア高気圧
Rainfall is heaviest between September and December because the onshore winds from the Siberian High are strongest, but it occurs throughout the year though least abundantly from April to August. Humidity is very high because of the marshy character of the coastal plains and can reach 90 percent in summer for wet bulb temperatures of over . The Alborz range provides further diversity to the land in addition to the Caspian coasts.