Run-by-run snow forecast

1. Four global models (ECMWF, GFS, ICON, GEM) are pulled hourly from Open-Meteo and blended. Their disagreement on summit snowfall sets the confidence level.
2. Every run is mapped from OpenStreetMap, and its top, bottom, aspect and steepness come from a digital elevation model.
3. Elevation: temperature follows a lapse rate fitted to the freezing level, so the rain/snow line lands on the right runs. Precipitation grows ~4% per 100 m, and colder snow is fluffier (Kuchera snow-to-liquid ratio).
4. Wind: new snow is loaded onto lee slopes and scoured off windward ones, mostly above treeline.
5. Sun: the real sun angle on each slope drives melt, crusts and spring corn cycles.
6. Segments: every run is simulated at its top, middle and bottom, so a long run can show powder up high and crust or slush lower down.
7. High-resolution models (HRRR, HRDPS, AROME, ICON-D2, JMA MSM) join the blend at double weight where they cover the resort.
8. Verified daily: forecasts are saved every day and scored against SNOTEL snow stations near US resorts.
9. People: groomed runs reset at 4 am; skier traffic tracks out powder and builds bumps through the day, faster on busy days.
10. Crowds: day of week, school and public holidays in each resort's markets, pass access, and powder days or bad weather.
11. Freshness: 100 is deep, dry, untracked snow. It drops with skier traffic, age, sun, warmth and rain; ✦ marks untracked runs.
12. Avalanche estimate: from 72 hours of new snow, wind loading, rain and warming. It is not a snowpack assessment; the official avalanche forecast always wins.
13. Grades: every factor runs A+ (best) to F, like Beach. A day inside the 10-day forecast is graded on the run simulation, weather and crowds; a later date on what it usually brings: typical snowfall, powder odds, the season's snow base, temperature and crowds.
14. Season outlook: snowfall so far this season, plus the 7-day forecast, plus the 10-season normal (ERA5 reanalysis at the summit) for the rest of the way to the date, nudged by ECMWF's seasonal forecast (SEAS5). Far out it is mostly the normal.
15. Past the 10-day forecast: the ten-day views start at the date you pick. Dates beyond the forecast show what they usually bring (the last 10 seasons plus the seasonal outlook), and the Runs and Safety tabs turn into predictions: the chance each run is open, from the snow predicted to have fallen by then and how deep it packs at the run's elevation, and the avalanche danger the date usually carries. They are estimates, labelled as such, and give way to the real forecast once the date is inside 10 days.
16. Places to stay: graded on distance to the lifts, restaurants and bars within a five-minute walk, guest ratings and the resort's grade that day.

Early-stage model with approximate resort data. Resort and patrol reports always win: check them before committing to steep terrain, and read the local avalanche forecast before going off-piste.