雨と風が体温を奪う 森林限界上は低体温警戒

Persistent rain will dominate Mount Yotei today, with summit temperatures hovering around 1 degree Celsius. The wind chill will make it feel below freezing, exacerbated by continuous strong drizzle and poor visibility of approximately 5 kilometers.

As an isolated peak, Mount Yotei is highly susceptible to strong winds and rapid weather changes, especially above the treeline at 1400 meters. Gusts up to 16.5 meters per second are expected during the day, which, combined with the rain, will drive the apparent temperature below -3 degrees Celsius. This presents an extremely high risk of hypothermia. Trails, particularly the long, direct ascent routes such as Hirafu and Makari, will be muddy, and exposed rocky sections will be slippery. Extreme caution is also necessary to prevent slipping near the crater rim.

For layering, a quick-drying synthetic or merino wool base layer, a fleece mid-layer, and a complete set of waterproof and breathable hardshell outerwear are essential. Waterproof gloves and a warm knit hat should also be carried. During any activity, prioritize staying dry, and if you feel your body temperature dropping, making the immediate decision to turn back is critical for safety.

Daytime activity under these conditions is strongly discouraged. Traversing the crater rim around the summit is particularly hazardous due to poor visibility, strong winds, and slippery surfaces, significantly increasing the risk of falls. While the weather is expected to improve in the early hours of June 9th, utmost caution is advised until then.