This week the temperature will drop in many Japanese regions.
In Hokkaido and some parts of Tohoku region will snow and temperature will be negative.
For the others regions (Such as Nagoya, Osaka, Fukuoka, and others) the temperature will be less then 10 Degrees. Only Okinawa will be around 20 Degrees.
Take care with the cold weather.
Source: Yahoo! Japan, The Japan Times.