When it starts
Alta, Dec 4–6, 2025: the model's run on the day said 5.0" skiable over 3 days, best Saturday at 4.3" (Nice day); the Atwater SNOTEL pillow gained 14" of depth. Model shy.
Model shy by 9.0". The usual direction: the 2025–26 backtest ran low on storm days.
Pack going in: 9" on Dec 3, 9" on Dec 4. The storm total counts from the first reading, so snow after 5pm the night before is in it.
| Day | Call | First chair | On hill | Skiable | Starts | Pillow before | Pillow after | Gain |
|---|---|---|---|---|---|---|---|---|
| Thu Dec 4 | Stay home | 0.0" | 0.0" | 0.0" | — | 9" | 19" | +10" |
| Fri Dec 5 | Stay home | 0.3" | 0.4" | 0.7" | ~8am | 19" | 24" | +5" |
| Sat Dec 6 | Nice day | 2.7" | 1.6" | 4.3" | ~10pm Friday | 24" | 23" | -1" |
Model: the run on the day (Open-Meteo Previous Runs, best_match). PowHound does not keep superseded live forecasts, so this is not the number you saw the night before. It is usually closer.
Clocks, local time: first chair 5pm–8am, on hill 8am–5pm, skiable is both. Stay home under 2", Nice day 2–8", Full Send 8" or more.
Pillow: snow depth at the Atwater SNOTEL station, read once a day around midnight. A day's gain is the next midnight reading minus that day's, so it runs midnight to midnight, not 5pm to 5pm. Depth is not snowfall: new snow settles and blows around, so the pillow usually reads under what fell. Not the resort report.
Verdict: close is within 3" or 30%. Season numbers and method: llms.txt.