Pay attention to weather forecasts
Look out for a rapidly developing low-pressure system, which tends to cause stormy weather. In large metropolitan areas such as the Kanto region, this can result in major traffic disruptions. And stay alert for a JPCZ, or Japan Sea Polar Air Mass Convergence Zone. This phenomenon causes heavy snow and blizzards. Do not go out at all if the Japan Meteorological Agency or transport ministry issue an emergency warning.
Know what to bring
If you must drive on a snowy day, it's important to prepare for the possibility of being trapped in your car for a long period. A portable toilet will prove essential, and so will warm clothing, blankets, a shovel, water and snacks.
Leave early, because driving in snow can take more time. Staying on major roads can be a lot safer, and if your car has a satellite navigation system, use it to avoid smaller sideroads, which can easily freeze over or be left uncleared. The transport ministry website features an easy-to-use "Snow Navi" service, including frequent updates and live cameras across Japan.
"Snow Navi" service (Japanese): https://www.hrr.mlit.go.jp/hokugi/yukinavi/