Data and scoring

Winter snowfall for 3,108 ski areas worldwide. 395 of them are in Japan, and for every Japanese one we also measure not just how much falls but what falls — the temperature when it snows, how often it snows, how often it rains instead, and the wind.

The 79 onsen towns designated by Japan's Ministry of the Environment are measured exactly the same way. Lists of onsen are easy to find; a list measured on the same ruler as the ski areas is not.

The point is not that any one place has been studied carefully. It is that everywhere has been measured identically. Comparability matters more here than the precision of any single value.

Snowfall is the sum of daily snowfall from December to March, averaged across the three most recent completed seasons. Southern-hemisphere resorts are calculated over June to September.

The source is Open-Meteo historical data on the ERA5 reanalysis — one calculation covering the whole world, which is what makes cross-border comparison possible at all.

Snow quality is built from four things: the temperature when it snows, how often more than 5 cm falls, how often it rains, and the wind on snowing days. How much snow falls is deliberately excluded — including it would make the quality ranking a restatement of the snowfall ranking.

The weights and thresholds are our judgement, not a measurement. Someone else would choose differently and the order would shift. What the ranking can carry is that every place went through one identical calculation.

The snowfall figures come from a reanalysis — an estimate, not a record of what fell. We checked how far off they are against 63 Japan Meteorological Agency weather stations.

They come to about six tenths of what was actually observed (mean ×0.60). They run low, and they run low by different amounts in different places: some read barely a third of the real figure, others match almost exactly.

We tried scaling everything by a fixed factor to correct for it. It barely helped, because the error differs from place to place. Having established that it cannot be fixed, we do not correct the figures — we say so instead.

The stations used for the check were chosen mechanically: within 15 km of a ski area, at most four per prefecture, nearest first. That rule exists so it can be verified that we did not pick convenient stations.

We do not forecast. What is published here is past observation and calculation, plus same-day information supplied by our weather data provider. We do not produce forecasts of our own.

Resort-published snow depths are a different thing entirely. Each measures in its own place in its own way, so those figures are not comparable to each other. Ours are comparable only because every location went through one identical process.

Questions about how these figures are produced, enquiries about using the data, and corrections to anything published here are all welcome through the contact page.