My travel to Japan in April 2008 went from south (Shikoku) to to the central part as Kamakura and Izu and further north of Tokyo with Nikko and Aizu-Wakamatsu. It gave the possibility to follow the cherry blossoms front and see some festivals.
Here is pictures from the Yayoi festival in Nikko in the Futurasan shinto shrine with a number of portable shrines, that is moved around. Here the parishioners is sitting in front of their shrines. Behind the shrines is food and sake.
This is from the Kamakura festival in Tsurugaoka Hachimangu shinto shrine. A group of persons from a lokal shrine is carrying a mikoshi. In this case is it from Egare Tenjin shrine. I visited that shrine later and saw the mikoshi return to the shrine. You can find pictures also from there.
At Matsuyama castle was a doll festival with dolls placed in the cherry trees. It was fine weather and many visitors.
Rain is not a problem if you will see the cherry blossoms. Here from Tsuruga castle in Aizu-Wakamatsu.