Interpreter Takezawa here!
Today, we’re back to learning about Mount Fuji.
Many readers of this blog are likely thinking about climbing Mount Fuji. However, Fuji has low temperatures, strong winds, and changeable weather, so checking the forecast before you go—whether climbing or just visiting—is essential.
Let’s dive into Mount Fuji’s climate.
Mount Fuji’s Temperature
The average temperature at the summit of Mount Fuji, based on 30 years of data from 1981 to 2010, is -6.2°C (20.8°F). From October to May, the average monthly temperature is consistently below 0°C (32°F).
The lowest temperature ever recorded was -38°C (-36.4°F) on February 27, 1981. The highest was 17.8°C (64°F) on August 13, 1942.
Mount Fuji’s Wind Conditions
The average annual wind speed on Mount Fuji is approximately 12 m/s (27 mph). It’s around 8 m/s (18 mph) in the summer and around 20 m/s (45 mph) in the winter. The summit experiences over 345 days per year with wind speeds exceeding 10 m/s (22 mph) and over 305 days with speeds exceeding 15 m/s (34 mph).
The highest instantaneous wind speed ever recorded was 91 m/s (204 mph) on September 22, 1966. On April 5, 1945, the maximum sustained wind speed (average over 10 minutes) reached 72.5 m/s (162 mph).
At 10 m/s, it’s impossible to walk with an umbrella. Above 15 m/s, it becomes difficult to stand. It can feel like a typhoon is hitting the summit of Mount Fuji every day!
Mount Fuji is 3,776 m (12,382 ft) high. The temperature drops roughly 0.6°C (1.1°F) for every 100 m (328 ft) of elevation gain. This is compounded by the wind. As an isolated peak, the wind sweeps up the mountainside, pushing the air upwards towards the summit.
This rising air expands due to the change in air pressure, which further cools the temperature. Winter temperatures can drop below -10°C (14°F) due to strong seasonal winds.
The average atmospheric pressure at the summit is 637.8 hectopascals, about two-thirds of sea-level pressure. The boiling point of water is 87.8°C (190°F), making it difficult to cook rice properly.
Also, sealed snack bags will inflate as you ascend due to lower air pressure.
Altitude sickness is also caused by lower air pressure, as the thinner air contains less oxygen.
Rainfall and Snowfall on Mount Fuji
The area around Mount Fuji receives an estimated 3,000 mm (118 inches) of precipitation annually (compared to the average of 1,700 mm or 67 inches in Japan). Snowfall is heaviest in spring (March-April) rather than in mid-winter. This is because winter pressure systems bring less precipitation.
This spring snow leads to “snowmelt landslides”, known as yukishiro in Japanese and 雪代 in Kanji, which are one of the weather-related hazards of Mount Fuji.
The yukishiro involves not just collapsing snow, but also rocks and debris, which can quickly overwhelm fields and homes in the foothills.
The town of Kamiyoshida, at the northern base of Mount Fuji, was originally located south of its current location (in an area called Old Yoshida) near the Sengen Shrine. It was relocated due to repeated yukishiro disasters. (Today, levees and retaining walls protect the town.)
In addition to yukishiro, Mount Fuji also experiences large-scale landslides at a place called Osawa Crag (大沢崩れ, Osawa Kuzure).
Osawa Crag is a massive gully extending from just below the summit down to an elevation of around 2,200 m (7,200 ft). It is constantly eroding Mount Fuji, with a maximum width of 500 m (1,640 ft) and a maximum depth of 150 m (490 ft).
The crumbling can be seen and heard from the distant Asagiri Highlands. About 160,000 cubic meters of earth and rock erode each year, equivalent to 32,000 dump trucks. Some theories suggest that if erosion continues, the gully will reach the summit in 1,000 years, splitting it in two. (The Ministry of Land, Infrastructure, Transport and Tourism’s Fuji Sabo Office is working to mitigate sediment disasters and other issues.)
Clouds over Mount Fuji
“Cap clouds” (笠雲, kasagumo) frequently form over the summit of Mount Fuji.
It’s often said that Mount Fuji wearing a cap cloud means rain is coming. While not always the case, it does increase the likelihood. Lenticular clouds are also commonly seen. Understanding cloud formations is essential when visiting Mount Fuji.
In Conclusion
Mount Fuji has well-maintained mountain huts and trails, but weather-related disasters can be life-threatening.
Understanding weather patterns and characteristics is crucial whether you’re climbing to the summit or simply exploring the base of Mount Fuji. Take care!
