The temperature on New Year's Day in Japan.

Check the weather forecast in all parts of Japan before you go. Yahoo Japan has. One year (2006), there was still heavy snow in Kansai from mid-June to February in 5438. I remember when we passed through He Zi County, there was snow about 10 cm thick everywhere. Ask before you go. It's fine to catch up with the weather. It is enough to have a down jacket in these cities. Just wear one under the down jacket.