Japan's climate varies considerably from north to south, and the timing of your visit can make a significant difference to what you see and feel.
Spring (March–May)
The most popular time to visit, and for good reason. Cherry blossom season (sakura) sweeps north across the country from late March in Kyushu and Tokyo to late April in Tohoku and early May in Hokkaido. The blossoms last only about two weeks in any given place; timing is imprecise and varies year to year. Parks fill with people sitting under the trees, eating and drinking — hanami (flower viewing) is a national obsession. Spring is also when new green appears on the mountains and the weather is mild and often sunny. Book accommodation well in advance.
Summer (June–August)
Hot and humid throughout most of the country, with a rainy season (tsuyu) typically running through much of June and into July. Tokyo in August can be brutal: 35°C and high humidity. That said, summer is festival season — fireworks displays, Obon dancing, and matsuri happen everywhere. Hokkaido is much more comfortable in summer and is worth considering if you want green landscapes without the southern heat. The typhoon season runs from August through October, with the strongest storms usually in September.
Autumn (September–November)
The second great season for visitors, when autumn foliage (koyo) turns the mountains and temple gardens spectacular shades of red and gold. Kyoto in November is beautiful but extremely crowded. Temperatures are cooler and comfortable, humidity drops, and the light is good. Hiking in the Japanese Alps and in Hokkaido is excellent in September and October.
Winter (December–February)
Japan receives serious snow in the mountains and on the Sea of Japan coast, making it one of the world's best destinations for skiing and snowboarding — Hokkaido in particular has light, dry powder that draws skiers from across Asia. The ski resorts around Nagano (hosts of the 1998 Winter Olympics) and Niigata are more accessible from Tokyo. Kyoto and Nara are quieter in winter and the bare trees around the temples have their own beauty. Onsen (hot spring baths) are particularly appealing in the cold. New Year is a major holiday when much of the country closes and domestic travel is expensive and crowded.
Avoid
Golden Week (late April–early May), the O-bon period (mid-August), and the New Year holiday all see enormous numbers of Japanese traveling domestically. Prices spike, trains are packed, and popular destinations can feel overwhelmed. Plan around these if you can.