Cherry Blossom Front (桜前線)
Cherry Blossom Front is a line graph illustrating the forecasted blooming dates of cherry blossoms (primarily of Someiyoshino (Prunus yedoensis)) in various locations of Japan. The term 'Cherry Blossom Front' was coined by the media which has been used since about 1967. This line graph shows that Cherry Blossom Front lands the southern Kyushu and Shikoku areas in late March, subsequently moving northward in ascending order of latitude values of locations starting from the northern Kyushu and Shikoku areas, the Seto Inland Sea coast, the Kanto region, the Hokuriku region, the Tohoku region and finally reaching Hokkaido in early May annually.
The Japan Meteorological Agency
Cherry Blossom Front is featured in the 'forecast of cherry blossom blooming dates' issued by the Japan Meteorological Agency beginning in early March. Cherry Blossom Front' is a coined term made up by the media and not an official terminology of the Japan Meteorological Agency. According to the data of the Japan Meteorological Agency, Cherry Blossom Front is referred to as the diagram of the forecast of cherry blossom blooming dates.
Reporting Method
In 1951, the Japan Meteorological Agency originally issued the 'forecast of cherry blossom blooming dates' mainly in the Kanto region. They, later on, extended the forecast to cover the entire country except for Okinawa Prefecture and the Amami region in 1965.
The Japan Meteorological Agency issues its first 'forecast of cherry blossom blooming dates' of the year on the first Wednesday of March. The agency subsequently continues to forecast cherry blossom blooming dates with appropriate adjustments on Wednesdays until the eighth report which is issued in late April. The cherry blossom blooming forecasts for the locations including Hokuriku, the Kanto-Koshin regions (which include Tokyo, Kanagawa, Saitama, Gunma, Tochigi, Ibaraki, Chiba, Yamanashi and Nagano prefectures), Tokai, Chugoku, Shikoku and Kyushu are issued during the first three reports of the year. That forecast covering Tohoku is announced during the third to the fifth reports, whereas, that for Hokkaido is issued during the sixth to the eighth reports.
When five or six blossoms have opened, the agency reports that cherry blossoms are 'flowering.'
If a few blossoms are open with the number of blossoms not meeting its definition of 'in bloom,' starting in 2009, the agency reports that cherry blossoms are 'about to bloom.'
According to the Japan Meteorological Agency, the approximate number of days between the time of 'flowering' and 'full bloom' (when over 80% of blossoms are in bloom) are 16 for the Okinawa and Amami regions, 7 for the areas between Kyushu and the Tokai/Kanto regions, 5 for the Hokuriku-Tohoku regions, and 4 for the Hokkaido region.
The agency explains that the farther north it is, the less number of days between 'flowering' and 'full bloom.'
If cherry blossoms come in to bloom within two days of the average date (based on the cumulative annual average over 30 years between 1971 and 2000), it will be reported as 'average.'
If, on the other hand, the deviation is three or more days, it will be reported as either 'early' or 'late' and, if the deviation is seven or more days, it will be reported as either 'pretty early' or 'pretty late' depending on the circumstance. In recent years, due to the global warming, the 'early' flowering report has been repeated every year.
Monitoring Method
There are 68 observation sites used by the Japan Meteorological Agency to monitor the flowering and full-bloom dates throughout Japan. The number of these sites, however, has been on the decline due to the continued closure of local meteorological stations. Someiyoshino is the main monitoring subject (whereas, Sargent or Chishima cherry in the northern and eastern Hokkaido, Kanhizakura in the Okinawa and Amami regions).
Cherry blossom buds begin to form during the summer of the previous year and become dormant as the low ambient temperatures set in for the fall and winter. After staying dormant during the fall and winter, the buds will develop and will come into bloom as the ambient temperatures rise in the spring. The timing of flowering of cherry blossoms is forecasted based on their characteristics that development of cherry blossom buds depends on ambient temperatures. Forecast used to be made by the respective observatories whereby they weighed buds collected from the sample trees at various locations for every forecast preparation. Since 1996, the Japan Meteorological Agency has been processing data collected nationwide using the computers located in Tokyo. The methodology used by the agency takes account on integrated values of average ambient temperatures between the fall of the previous year and the current month based on data on flowering dates and average ambient temperatures in the past, the actual and forecasted ambient temperatures during the current year.
Topics of 2007
Due to some problems in the software to perform calculation, the Japan Meteorological Agency published the wrong forecasted dates for four locations including Tokyo and Shizuoka in the first report of 2007. The agency consequently made corrections and issued an apology during the second report of March 14.
Cherry Blossom Front used to move northward from Kyushu toward northeast approximately in ascending order of latitude values of locations. In recent years, however, Cherry Blossom Front has sometimes moved in a complex curving line. It is, in particular, characterized by the reversal of the normal geographical order whereby flowering starts in the northern Kyushu and the Honshu earlier than that in the southern Kyushu.
It is considered to be caused by a phenomenon referred to as 'dormancy breaking.'
It is the condition that, due to the recent climatic tendency for unusual warm winters, dormancy, which is essential to bring cherry blossoms into bloom, becomes disrupted as ambient temperatures do not stay sufficiently low for a certain period of time in the winter, resulting in their late blooming. For example, according to the 'forecast of cherry blossom blooming dates' issued on March 14, 2007 by the Japan Meteorological Agency, cherry blossoms in Tokyo were expected to bloom earlier than those in Kagoshima City. Cherry blossoms in the center city of Tokyo (with sample trees being located on the grounds of the Yasukuni-jinja Shrine) actually came into bloom on March 20 being the earliest in the country for the year. Additionally, a few hours prior to announcing the flowering in Tokyo, the Japan Meteorological Agency reported during their third forecast of cherry blossoms flowering dates that it was forecasted for March 22. That forecast did not reflect the real situation where a few blossoms had been open for the past couple of days. This error was caused by the current methodology of forecasting flowering dates which does not take in consideration the actual flowering process of cherry blossoms which can be detected by observing how buds are developing.
Other
Weathernews Inc. develops the 'Cherry Blossom Flowering Forecast Map' based on its own research aside from that of the Japan Meteorological Agency. That company provides detailed forecasts corresponding to the locations renowned for cherry blossoms.
The Japan Weather Association develops the flowering forecast mainly for urban areas based on its own research as well. There are more observation sites than those of the Japan Meteorological Agency (as of 2008).