Japan is a temperate region with four seasons of varying severity--five, if the rainy season is included. Japan's average temperature for the summer time is 30°C, and for the winter, it is 4.7°C. Because of its great length from north to south, Japan's climate varies from region to region: the far north is very cold in the winter, while the far south is subtropical. The climate is also affected by the seasonal winds, blown from the continent to the ocean in winters and vice versa in summers. The waters of the Kuroshio Current also warm the Pacific side of Japan, sustaining the coral reefs of Japan, the northernmost coral reefs in the world. Due to severe water pollution, these reefs are now dying.

The extreme cold in a Sapporo winter allows construction of a snow palace

Japan's main rainy season begins (tsuyu-iri) in early May in Okinawa, and the stationary rain front responsible for this gradually works its way north until it dissipates in northern Japan before reaching Hokkaido in late July. The rainy season begins in most of Honshu around the 8th of June and ends (tsuyu-ake) around the 20th of July. In late summer and early autumn, typhoons develop from tropical depressions generated near the equator, and track from the southwest to the northeast, often bringing heavy rain.Japan's varied geographical features divide it into six principal climatic zones:

• Hokkaido: Hokkaido has a temperate climate with long, cold winters and cool summers. Precipitation is not heavy, but the islands usually develop deep snow banks in the winter.
• Sea of Japan: The northwest wind in the wintertime brings heavy snowfall. In the summer, the region is cooler than the Pacific area, though it sometimes experiences extremely hot temperatures, due to the Föhn wind phenomenon.
• Central Highlands (Chuo-kochi): A typical inland climate, with large temperature differences between summer and winter, and between day and night. Precipitation is light.
• Seto Inland Sea (Seto-naikai): The Mountains of the Chugoku and Shikoku regions block the seasonal winds, bringing mild weather throughout the year.
• Pacific Ocean: Experiences cold winters with little snowfall and hot, humid summers due to the southeast seasonal wind.
• Nansei-shoto (Ryukyu) or Southwest Islands: The Ryukyu Islands have a subtropical climate, with warm winters and hot summers. Precipitation is very heavy, especially during the rainy season. Typhoons are common; in 2004 a record 10 typhoons reached the main islands.