After a long winter (December-March), April is the beginning of Japan's relatively short spring (April-May). Temperatures are generally much warmer than in the winter, but not as stifling as in the summer, making April a great month to travel to Japan.
In general, the further north you go in Japan, the colder the temperatures. Northern parts of Japan (Hokkaido, Tohoku) will still be quite cold in April. In Sapporo, capital of Hokkaido, expect average highs of 52° F (11° C) and lows of 37° F (3° C). The major cities on Honshu and Kyushu (Tokyo, Osaka, Kyoto, Fukuoka) experience warmer daytime temperatures, with average April highs in these cities of around 66° F (19° C), and lows of 52° F (11° C). Sub-tropical and tropical Okinawa is even warmer, with average highs in Naha of 75° F (24° C) and lows of 66° F (19° C).
Japan's wet season is the summer, so there's not much rain anywhere in April. But, there's still a chance of snow in northern areas, especially Hokkaido.
Japan's famous hanami, or cherry-blossom-viewing parties, start in mid-late March and continue into April, as the flowers bloom at different times depending on temperatures across the country. While the best of the cherry blossoms may have been-and-gone in Tokyo and places further south by April, you can still catch them in Tohoku or Hokkaido (and even into May in Hokkaido).
Crowds and Costs
April is quite a busy time in Japan, because not only do more foreign travelers come than in the winter, but there are many Japanese holidays throughout the month. Earlier in April, schools take their spring holidays (often starting in late March), while later in the month is the start of Golden Week, a week-long period where a lot of public holidays fall, and when many Japanese take annual leave. Many attractions are very busy during the Golden Week holidays, and availability of shinkansen trains and domestic flights may also be very limited. If you know you're going to be traveling to Japan during this major holiday period, book everything as far in advance as possible or expect to pay high prices (if you can make bookings at all at the last minute, that is).
Where to Go
There's hardly a bad place to go in Japan in April, because even in the northern areas, where temperatures will be cooler, daytime highs will be comfortable for getting out and about.
If you're visiting during the busy Golden Week holiday period, it would be best to avoid really popular destinations, such as Nikko, Mt. Fuji, or Kyoto.
At other times of the month, conditions are great in these popular places. But to get away from lingering crowds, check out more remote areas that aren't on the beaten tourist path, such as the island of Shikoku (Japan's 'fourth' island), or the northern Tohuku region of Honshu.
What to Do
April is a great time to enjoy some outdoor activities, because temperatures are comfortable but not generally too hot for activities like hiking. Although much of Japan is very urban, there are also many places that aren't, and Japanese themselves like to hike. You can find beautiful mountain trails within close proximity of Tokyo, such as the Chichibu-Tama-Kai National Park, or the area around Nikko. The island of Shikoku or the Japan Alps mountains offer more remote trails that are great for multi-day treks.
Hanami—cherry blossom viewing parties. Cherry trees bloom from mid-March until late April or even early May in Hokkaido, sweeping up the country. Cherry blossom viewing parties are a favorite annual pastime of many Japanese, so these parties are a chance to enjoy nature and culture.
Golden Week. This is actually a collection of four holidays that fall within a week, from April 29 to May 5. These holidays are Showa Day, Constitution Day, Greenery Day, and Children's Day. Various events are held in observance of these individual holidays, and many people take the full week off work in order to maximize their time off.
Traveling to Japan in April? Check out these great itineraries
Self-Guided Walking Tour on the Nakasendo Trail - 10 Days. Take a walk through time on this 10-day self-guided tour of the Nakasendo Trail, part of feudal Japan's original network of highways. Travelers on the mountain path between Kyoto and Tokyo took several days to travel the distance, staying overnight in Juku post towns.
Explore Japan: Tokyo & Kyoto - 5 Days. This five-day trip to Japan is packed with experiences to make the most out of your time. Covering Tokyo and Kyoto, this trip has all you need to experience two completely different, yet equally beautiful, sides of Japan.
Explore the Golden Route of Japan - 12 Days. Explore the high-energy tech and fashion of Tokyo, enjoy the breathtaking views and temples of Kyoto, relax at a hot spring retreat in Hakone, and feast on the exceptional cuisine of Osaka.