How HuttWatch works

The methodology, the honesty rules, and what the numbers mean.

What this is

HuttWatch answers one question for 9 New Zealand ski fields: what's the chance this mountain is fully closed tomorrow? It's built for the evening decision — whether to commit to the drive — and for the 7am check before you leave.

Where the numbers come from

Every evening we make one official call per mountain for the next day, and it never changes afterwards — the exact time it locked is stamped on the call itself. The inputs: a multi-member weather forecast ensemble (wind gusts, snowfall, precipitation, freezing level) for each field's own coordinates, the NZ Avalanche Advisory for its region, and that mountain's own closure history. Through the day, a live re-read recomputes the same model on the freshest forecast every 30 minutes — clearly labelled, never mixed into the official record.

Not every mountain has earned a full model, and we say so on every card. TUNED TO THIS MOUNTAIN means we have learned how that mountain behaves from its own past forecasts and what it actually did on each of those days. BASED ON ITS HISTORY means how often it has actually been shut on days like tomorrow, counted from its own record — real, but rougher than a full model. FLAG ONLY means we can name the mechanism that closes it but haven't earned enough of its data to price it. NO RATE YET means we have not measured a closure rate for that mountain: the number shown is our starting default rate, the same one we would use for any unmeasured mountain, and it is not that mountain's own. LAST NIGHT'S CALL means we could not re-run the numbers for that day, so what you are seeing is the locked call, not updated with today's forecast.

The honesty rules

Calls freeze once they are locked. Each call is locked in the evening, before the mountain has posted anything, and carries the exact time it locked; it is never revised afterwards. A prediction revised after the mountain posts its morning report isn't a prediction. The scored record contains only night-before calls.
No hindsight in training. Models only ever see what a forecast said the night before — never same-day observed weather.
Every call stays on the record, right or wrong, from the moment it's made. The track record shows each one against what actually happened.
No guessed outcomes. A day shows as open or closed only when a mountain's own report said so; missing days stay visibly missing.
Stale data announces itself. If our pipeline breaks, the site says so rather than presenting old numbers as fresh.

The record so far

Night-before calls made this season	502
Scored against real outcomes	499
On the right side	402

The honest caveat we repeat on the record page: the record is short, and it has already got some hard days in it — see Tūroa and Whakapapa, where we have been calling the risk higher than it has turned out. Every call lands on the record, whichever way it goes.

Independence

HuttWatch is an independent Canterbury-based project. We are not affiliated with any ski field or operator, we link to every mountain's official report on its page, and the standing advice is printed on every card: always check the mountain's own site before you drive. Live status shown on HuttWatch is quoted from the operators' own published reports, with their timestamps.

Questions or corrections

Use the feedback button on the main page — every note gets read.