There are three well-defined seasons: the hot-weather season, lasting from March to mid-June; the season of southwest monsoon rains, from mid-June to October; and the cold-weather season, from November to February. May is the hottest month, with the mean temperature exceeding 90 °F (32 °C), except in the extreme north and the plateaus of
Ranchi and Hazaribagh. (Because of its agreeable climate, Ranchi city had historically served as
Bihar's summer capital.) The normal annual rainfall varies from 40 inches (1,016 mm) in the west-central part to more than 60 inches (1,524 mm) in the extreme north and in the southwest. The rainfall on the plateau—more than 50 inches (1,270 mm)—is heavier than on the plains. Nearly all the rain (85–90 percent) falls between June and October, and nearly 50 percent of the annual rain falls in July and August. The cold-weather season is the pleasantest part of the year.