How Can The Weather-forecasters Forecast The Date Of Sakura Blooming?

As I wrote yesterday, Japanese weather-forecasts include "Sakura (Cherry Blossoms) Blooming Forecast", and according to Japan Weather Association, the start date of Sakura blooming for this year would be March 21st and the date of full bloom would be March 28th in Tokyo area.

However some Sakura trees are already blooming as shown in the lower photo since there are many different kinds of Sakura trees in Japan. We have early blooming types (famous one for it is Kawazu-Zakura), and late blooming types (Yae-zakura, double-petal Sakura is a typical late blooming type). 

What is then the meaning of the forecast when they say the date of Sakura blooming and the date of full blooming in "Sakura Blooming Forecast"? Actually they are mostly forecasting about the most common type of Sakura called "Someiyoshino". This Sakura type was bred during the late Shogunate (Samurai) era, and since it grows quickly and the flowers are beautiful, it was spread over the country and became the most common Sakura.

Of course, even the same type of trees in an area can start blooming on different days, but since the "Sakura Blooming Forecast" has a long history as a formal forecast, the Meteorological Agency of Japan has a Standard-Sakura tree in each area. In Tokyo area, the Standard-Sakura tree is a Someiyoshino tree and it is located in Yasukuni Temple in Chiyoda-ward. Thus the start date of Sakura blooming in Tokyo is the date when the Standard-Someiyoshino in Yasukuni Temple starts blooming.

Apparently the Meteorological Agency of Japan started the "Sakura Blooming Forecast" in 1953. Since then, they kept the Standard-Sakura trees all over Japan which are 59 trees in total. In other words, there are Sakura trees working for Japanese government offices. Their task is very important to live up to Japanese people's expectations for Hanami (Flower viewing) with perfect timing.