Writing about how ski tracking actually works — measurement, honest estimates, open data, and what a no-server app can and can’t do. Every number here traces to the app or a named source.
How fast were you really going? Ski app top speed, honestly — Every ski app shows a top speed. Almost none show the measurement error. Why GPS speed has error bars and why Alpy prints them.
Personal records for skiing: every named run is a segment — How Alpy builds a PR board from your ski days — verdicts on every descent, a race chart against your best, and why partial runs never count.
Epic, Ikon, Mountain Collective, Magic Pass: who covers what — Pass coverage across 51 verified resorts for 2026/27, checked against the official pass sites — and why apps shouldn’t guess about passes.
The 2026/27 season-opening checklist: body, gear, data, mountain — A practical pre-season checklist for skiers: leg prep that actually transfers, binding checks and what to tell the shop, pass math for 2026/27, avalanche kit practice, and setting up your phone before first chair.
How to read an avalanche bulletin (and why your ski app should show the real one) — The five-step danger scale, critical aspects and elevations — and why Alpy shows official SLF and avalanche.org bulletins verbatim instead of summarizing them.
Powder alerts: how to hear about fresh snow before the lifts open — What a powder alert is, where the snow data comes from, and how Alpy’s background alerts work without a server or an account.
The phone in your pocket is a ski lab: GPS, barometer, accelerometer — A long look at the three instruments inside an iPhone, what each one can and cannot measure on a mountain, and how fusing them produces honest ski telemetry — vertical, airtime, turn load, and error bars.
The 3,652 ski areas OpenStreetMap knows about — We indexed every named winter-sports area in OpenStreetMap — 3,652 of them worldwide. What that data makes possible for a free ski app.
On-device AI for skiers: a morning report that never phones home — How Alpy uses Apple’s on-device foundation model to write morning reports and day summaries — and the never-invent rule that keeps the AI honest.
A ski app with no server: what that actually means — Alpy has no backend at all — no accounts, no sync, no analytics. What a no-server architecture changes about privacy, and what it honestly costs.
How ski apps measure vertical — and why GPS lies about it — GPS altitude wobbles 10–20 m on a mountain. How barometer fusion gives a ski tracker honest vertical, and what Alpy does differently.
Counting ski turns from GPS: an honest estimate — How a phone estimates turns from heading swings, why the number has a tilde in front of it, and what turn cadence says about fatigue.
Ghost racing: racing yourself down a ski run — How Alpy turns every named piste into a segment and lets you race your own fastest descent — live on the mountain and in a 3D replay.
The freeze curve: the one chart that explains your ski day — What the freezing level is, how it moves through a day and a storm, how to time soft snow and avoid boilerplate ice — and how Alpy draws the curve from forecast data.
Free ski tracking on iPhone in 2026: what you actually get — What the free tiers of ski tracking apps include, what sits behind subscriptions, and what a genuinely free app looks like.
Fatigue, turn cadence, and the myth-proof case for skipping the last run — What your turn rhythm reveals about tiring legs, how Alpy’s Day Rhythm chart detects the fade, what heart-rate data adds — and an honest look at ‘most injuries happen on the last run.’
Why our trail maps are drawn, not painted — The strange world of ski resort panorama art, why apps can’t just bundle it, what OpenStreetMap geometry offers instead — and how Alpy renders a mountain twice: schematic chart and 3D terrain.
How we built ghost racing for skiing: a technical deep-dive — The full engineering story: turning OpenStreetMap pistes into segments, the partial-descent problem, inverting the descent profile for F1-style deltas, and racing a ghost live on the mountain.
Alpy is a free, privacy-first ski app for iPhone. What it does · Alpy vs Slopes · Resort data