Japan: Adverse weather forecast across much of the country through at least Dec. 20

Adverse weather conditions are forecast across much of Japan through at least Dec. 20. The Japan Meteorological Agency has issued a severe weather bulletin advising a cold front will bring lightning, strong wind gusts, hail, and possible tornadoes across eastern and western Japan through Dec. 19. Heavy snowfall is also forecast over areas along parts of the Sea of Japan coast through at least Dec. 20, as well as over some inland mountainous areas. As of Dec. 18, the Japan Meteorological Agency has red blizzard warnings (the middle level on a three-tier scale) for parts of Fukuoka and Yamaguchi prefectures. Yellow weather warnings for heavy rainfall, heavy snowfall, strong winds, thunderstorms, rough seas, low temperatures, and avalanches are in place across various other parts of the country. Authorities will likely issue new alerts or update/rescind existing advisories as weather conditions change over the coming days.

The storms could produce rounds of heavy precipitation (including rain and snow), strong winds, and isolated thunderstorm activity in affected areas. Where precipitation falls as rain, flash and areal flooding is possible. Such flooding is possible in low-lying communities near watercourses and other large bodies of water, as well as in urban areas with easily overwhelmed stormwater drainage systems. Sites located downstream of large reservoirs may be subject to flash flooding after relatively short periods of intense rainfall.

Precipitation could fall as snow in parts of the country over the coming days. Wind gusts could cause blowing and drifting snow; decreased visibility is likely in affected areas. Rain-induced landslides cannot be discounted in areas of elevated terrain; there is also the possibility of avalanches in mountainous areas where the snowpack has become unstable due to heavy snowfall. Power outages could occur throughout the affected area.

Floodwaters and related debris may render some bridges, rail networks, or roadways impassable, impacting overland travel in and around the affected area. Flooding in urban areas could also result in significant traffic congestion. Heavy snow will likely make driving hazardous in some areas; authorities could implement temporary road closures or detours in such locations. Mountain passes and tunnels could be closed as a precautionary measure during periods of intense snowfall.

The disruptive weather will likely cause some delays and cancellations at airports in parts of Japan. Authorities may temporarily suspend port operations in coastal areas if strong winds trigger hazardous sea conditions, impacting freight and passenger maritime traffic. Flooding or snow could block regional rail lines; freight and passenger train delays and cancellations are possible in areas that see heavy rainfall and potential track blockages.