Updated: Jan 23, 2019
January 20th (Yesterday) was called "Daikan", or the coldest season, which is one of the 24 seasons of the lunar calendar. This system is originated in ancient China, and it is still used in China, Korea, Vietnam and Japan. Japan has adopted solar calendar about 150 years ago and our everyday life is bound by the calendar, people often refer to the 24 seasons. Honestly, as this system was invented in China and in accordance with Chinese climate, it is slightly unmatched with Japanese climate. But Japanese value the changes of the seasons and adopted the 24 seasons system in daily life.
Though Daikan means the coldest season in a whole year, this year the situation is a bit different. According to the weather report, it reached 16 degrees centigrade in the suburb of Tokyo yesterday. It is almost a temperature in April, isn't it! In general, it is not very cold this winter. Is it an effect of global warming? I am not so sure, but one thing I am sure is that winter in Tokyo is much colder than now in my childhood (40 years ago). I was living in a wooden house then, while I am living in a concrete studio now...
I definitely say that the coldest season in Tokyo is beg/mid January. We may have some snows in February, but it is not very cold when it snows. Plum trees will start to bloom soon in February and lots of people come out of their rooms to see, smell, and appreciate it. In Tokyo, Koishikawa-Korakuen, a Japanese landscape garden, is very famous for plum trees transplanted from Kairakuen, one of the 3 major parks in Japan. It is worth visiting in the peak season.