How do we know SAKURA season?
Many foreign travelers express their wish to come back to Japan during SAKURA (桜）, or cherry blossom season．However, the blooming season is very short, and it changes slightly each year.
How do Japanese know the right timing to see sakura?
Every year the Japanese Meteorological Agency and the public track the sakura zensen (桜前線 cherry blossom front) as it moves northward up the Japanese archipelago with the approach of warmer weather via nightly forecasts following the weather segment of news programs.
The blossoming begins in Okinawa in January, and typically reaches Kyoto and Tokyo at the end of March or the beginning of April. It proceeds into areas at the higher altitudes and northward, arriving in Hokkaido a few weeks later.
During the Sakura season, Japanese pay close attention to these forecasts and turn out in large numbers at parks, river banks, Shinto shrines and Buddhist temples with family, friends, couples, colleagues to hold flower-viewing parties called hanami . Many bring their box lunches, snacks .....caned beers or sake, etc. to relax and enjoy the beautiful views.
The custom of hanami is believed to dates back many centuries. According to the 8th century chronicle "Nihon Shoki (日本書紀)" , hanami festivals being held as early as the 3rd century AD.
From Japan -guide.com , you can get the latest Cherry Blossom Forecast in English.