How it works
One question, answered honestly every morning: is it a powder day in Niseko? Here is exactly how we answer it.
Where the numbers come from
Measured: the Japan Meteorological Agency (JMA) AMeDAS station in Kutchan town — 倶知安 (Kutchan) (#16217), 176 m above sea level. Snow depth and new snow are measured every hour; temperature, wind and precipitation every 10 minutes.
Kutchan is a town, not the mountain: it is usually warmer and gets less snow than the slopes, and it can rain in town while it snows up top. We always label these numbers “town”.
Forecast: Open-Meteo, using JMA’s own high-resolution models (MSM 5 km, then GSM) for snow, temperature and wind, and Open-Meteo’s best-match models for gusts and freezing level. We ask for three points on the mountain:
- Summit: 42.8755, 140.658 at 1300 m
- Mid-mountain: 42.8672, 140.6795 at 820 m
- Base (Hirafu): 42.859, 140.701 at 280 m
Season tracker: daily snowfall and snow depth from JMA’s past weather data for the same Kutchan station (block 47433), back to the 2016-17 winter. The current season is read again every morning. /season
A Cloudflare Worker fetches both sources once an hour and stores the result. Your visit never calls JMA or Open-Meteo directly. If a source is down we keep showing the last good data and say how old it is.
The powder score
A transparent rule of thumb from 0 to 100 — not an official forecast. It starts from fresh snow and is adjusted for quality and conditions:
- Fresh snow in the last 24 h: the larger of what Kutchan measured and what the model says fell at mid-mountain. 3 cm ≈ 10 points, 10 cm ≈ 40, 20 cm ≈ 65, 30 cm ≈ 80, 50 cm+ ≈ 95.
- More snow forecast in the next 24 h: +1 point per cm, up to +15.
- Cold and light (mid-mountain ≤ -8°C): +5. Warm and heavy (≥ 0.5°C): −15.
- Wind over the next 6 h: breezy (≥ 10 m/s mid-mountain) −8; lift holds likely (≥ 15 m/s, or summit gusts ≥ 22 m/s) −20.
- Rain at the base in the last 24 h (≥ 2 mm): −10.
- No fresh snow means no powder: without at least 1 cm the score can’t reach “Kinda.”
Verdicts: 75+ “YES!”, 50+ “Yes.”, 25+ “Kinda.”, below that “Nope.”
These thresholds will be tuned against real winter mornings. Disagree? That’s half the fun.
Honest limits
- Forecasts are model estimates. Mountains make their own weather, and Niseko’s famous snow often comes in bands models miss.
- Out of season, JMA doesn’t measure snow depth in Kutchan, so those numbers show as “not measured”.
- Nothing here is about safety. For lifts, gates and avalanche conditions, always check the official sources.
Privacy & credits
Free and non-commercial: no ads, no cookies, no tracking. Observations: Japan Meteorological Agency. Forecast data: Open-Meteo.com (CC BY 4.0). Raw data for your own projects: /api/conditions.json.