Chasing Clear Skies: Weather and Hiking in Japan

Reading Japan’s Mountain Weather Before You Hike

After twelve years of hiking and writing this blog, I’ve probably spent more hours than is healthy poring over weather forecasts, scrolling through apps, and second-guessing predictions. I’ve been wrong about as often as I’ve been right, but over time I’ve realised that precision isn’t the point. It’s about improving your odds—stacking the deck just enough in your favour before arriving at the trailhead.

Take last week. I set my alarm for five, half-expecting I’d head straight back to bed. The three-day hike I had in mind, up to Mt. Oku-Hotaka, was hanging in the balance. The forecast had been shifting like a restless sleeper—first promising sunshine, then hinting at rain, then flipping back again. What I needed most was one clear day, just enough of a window to make my bid for the summit worthwhile. Sitting there with coffee, staring at the latest update, weighing “green” against “blue” on a popular weather site, I decided to chance it. By evening, camped beneath the Hotaka massif under clear skies, it felt like I’d pulled the right card.

I don’t claim to have any secret formula—I don’t think anyone does—but I’ve learned where to look. Over the years, Tenkura Tenki to Kurasu and Tenki have become my go-to sources, with Weathernews and Yamaten filling in the gaps. Tenkura, in particular, with its A–B–C rating, is especially handy. But the real winner comes at 6:50 pm, when NHK delivers its nightly forecast. No algorithm has matched the straightforward accuracy of that broadcast.

Just as important as knowing what to trust is knowing what to ignore. Mountain-Forecast may look promising—especially with its English interface—but in practice, it leans so far toward caution and pessimism that it’s practically unusable. The slightest chance of inclement weather, and the whole day gets painted with rain and cloud. If I had relied on it all these years, I’d hardly have left home.

Still, even the best forecasts are only hints of what might unfold. The real trick is watching the trend, not the snapshot—seeing whether things are nudging toward improvement or decline. More often than not, that subtle drift makes the difference. And then there’s intuition, the hiker’s sixth sense, honed over countless mornings like last Sunday, when I sat over a bowl of Weetabix and decided, despite all the ambiguity, to just go.

From there, the consequences of making such a late decision quickly followed: snagging one of the last bus tickets to Kamikochi, sitting through half the Azusa ride on the floor like a teenager at a summer festival, and finally watching the weather break—thankfully, at least this time—in my favour. This is one of the clear advantages of camping over staying in huts: the flexibility to shift plans on a dime. I don’t mind the odd wet afternoon on a multi-day hike; that comes with the territory. But like anyone, I’d rather have clear views, whether from a ridgeline or a summit. And, as a blogger, it’s a lot harder to muster the motivation to write up a trip when half the photos are nothing but slabs of cloud.

The flip side, of course, is knowing that forecasts ebb and flow, and sometimes it’s worth throwing caution to the wind. Those gloomy-looking mornings often turn out far better than expected. In the end, that’s part of the adventure: learning to read the sky, trusting your judgment, and at times just heading out anyway.