How it works
We look at what actually fell on your exact dates in every past winter on record, and count how often there was at least one powder day. No forecasts, no guesswork: just what happened, year after year.
What counts as a powder day
15 cm (about 6 in) or more of new snow in a single day. The rule is the same for every resort, so you can compare the percentages fairly: a resort scores higher because it really gets more big snow days, not because we judged it differently.
How we work out your odds
- You pick a resort and your trip dates.
- We take those same calendar dates in every past winter, back to the start of the station's record.
- For each winter, we check whether any day in that window had a powder day.
- Your odds are the share of winters where at least one day of your trip was a powder day.
Niseko United, 18–27 January: in 59 of the last 74 winters (since 1952/53), at least one of those days was a powder day, so the odds are 80%.
That's the chance your whole trip gets one or more powder days, not the chance for any particular day. Longer trips get higher odds: more days, more chances.
The results page also shows:
- How many powder days: how often past trips got none, one, two or more, and your chance of at least 1, 2 or 3.
- Expected snowfall: the median total for your dates (half of winters got more, half got less), and the range the middle half of winters fell in.
- Every winter, same dates: a bar for each winter, so you can see good and lean seasons for yourself.
Which winters count
Each "winter" is one past year's version of your trip. For 18–27 January, that's 18–27 January 1953, 1954, and so on up to last season. It's labelled by season, so January 1953 shows as 1952/53.
A winter only counts if every day of your trip was measured that year. If even one day is missing from the record, we leave that winter out rather than guess. A missing day is never treated as a day with no snow.
When fewer than 10 winters have a complete record for your dates, we mark the result with a ~ and a low-confidence warning: one unusual season can swing it a lot.
Where the data comes from
Snowfall is measured daily at official weather stations, not estimated by a computer model. Models tend to badly undercount snow in the mountains, so we only use one, clearly labelled, where there's no station with a long record nearby.
The stations are usually in town, below the ski area, so the slopes typically get more snow than the numbers show. Use them to compare resorts and dates, not as an exact depth on the mountain.
| Resort | Station | Distance | Station height | Records since |
|---|---|---|---|---|
| Myoko Kogen | Sekiyama (関山) | 7.9 km | 350 m | 1980 |
| Niseko United | Kutchan (倶知安) | 12.9 km | 176 m | 1953 |
- Sekiyama: JMA AMeDAS automatic station, Myoko. Before 2009 snow was only observed in the main season (roughly Dec-Mar); other months are NULL in those years.
- Kutchan: JMA staffed station. Snowfall before the 2005/06 season was recorded by a different method; snowfall_cm for those years is quantile-mapped onto the modern method month by month (snowfall_raw_cm keeps the published value).
What it can't tell you
- It's not a forecast. It tells you how often your dates delivered in the past. Any single winter can be better or worse.
- It doesn't judge snow quality: how light the snow was, wind, or whether lifts were running.
- It doesn't yet factor in El Niño or La Niña. We tested it on our data and found no clear effect at Niseko and only a weak one at Myoko, so for now every winter counts equally.
Data credits
Japan Meteorological Agency (出典：気象庁ホームページ). Processed by givemepow.
We clean and process the published data before using it (for example, marking unrecorded days and adjusting for changes in how a station measures snow), so the numbers here aren't a direct copy of the original records.