Alta Ski Area — Rain Susceptibility
Based on 1986-87 through 2025-26 (40 ski seasons) of historical ERA5-Land weather data.
Score version: RSS_V5_PERCENTILE_COMPOSITE_DEC1_APR15_1986_2026 · calculated Sep 27, 2026 · dataset: reanalysis-era5-land-timeseries
| Alta Ski Area | |
|---|---|
| Rain Susceptibility Score (0=low, 100=high) |
5 |
| Rain Resilience Score | 95 |
| Overall Confidence | MODERATE |
| Percentile: future rain (+2°C) | 4.6 |
| Percentile: conversion exposure (+2°C) | 4.6 |
| Percentile: significant rain days (+2°C) | 9.1 |
| ERA5 grid location | 40.6, -111.6 — grid elevation 2633 m |
| Ski-season precip climatology | 340 mm/season across 724 precip hours/season |
Observed history: 1986-87 to 2025-26
Not a stress test — this is the actual real weather record, at the same elevations, with no synthetic warming applied. Compare its size to the hypothetical +1/+2/+3°C scenarios below to see how much warming has already happened vs. how much more the stress tests represent.
Each point is one real ski season's precip-weighted rain fraction — not smoothed or averaged, so year-to-year variability (a wet La Niña year, a dry cycle, etc.) is visible directly rather than hidden inside a multi-year average.
| Alta Ski Area | |
|---|---|
| 1986-87 to 2005-06 (first half avg.) | 0.90% |
| 2006-07 to 2025-26 (second half avg.) | 0.72% |
| Observed change (half-vs-half average) | -0.18% points |
Rain fraction by elevation band and warming scenario
Precipitation-weighted share of ski-season precipitation estimated to fall as rain, not snow.
| Band | Elevation | vs. grid elev. | Confidence | Current | +1°C | +2°C | +3°C |
|---|---|---|---|---|---|---|---|
| Base | 2600 m | -33 m | GOOD | 1.5% | 3.1% | 6.4% | 12.1% |
| Mid | 2908 m | 275 m | GOOD | 0.5% | 1.1% | 2.2% | 4.6% |
| Summit | 3216 m | 582 m | MODERATE | 0.1% | 0.3% | 0.7% | 1.5% |
Rain fraction vs. warming, by elevation band
Underlying conditions during precipitation (geeky detail)
Precip-weighted distribution of wet-bulb temperature, dry-bulb temperature, and relative humidity during ski-season precipitation hours -- the actual data behind the rain fraction above, plus the phase curve applied to it. Not used in scoring; here purely for transparency.