The climate of Japan varies from region to region and is influenced by geography, ocean currents and seasonal winds. As with most countries in the temperate zone Japan has four main seasons with the rainy season (June) perhaps its 5th season and the typhoon season (August- October) perhaps the 6th.

In Spring (March, April, May), the temperatures are warm but not hot, there is not too much rain, and March-April brings the justly famous cherry blossoms (sakura) and is a time of revelry and festivals. 

Summer (June, July, August) begins in June with the rainy season (known as tsuyu or baiu) and turns to extreme humidity and high temperatures in July and August. The upside, though, is a slew of fireworks shows (hanabi taikai) and festivals big and small. 

Autumn (September, October, November), is an excellent time to be in Japan. Temperatures and humidity drop and the autumn colors can be just as impressive as the cherry blossoms. However, typhoons often hit the southern parts of Japan bringing everything to a standstill in early autumn. 

Winter (December, January, February) characteristically brings snow (sometimes very heavy) to the north and west of Japan while it remains dry, clear and crisp on the more populated east.

For an overview of weather data and statistics for most cities in Japan, please visit this page and select a location.

http://www.data.jma.go.jp/obd/stats/data/en/smp/index.html