Keystone Resort — 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
| Keystone Resort | |
|---|---|
| Rain Susceptibility Score (0=low, 100=high) |
4 |
| Rain Resilience Score | 96 |
| Overall Confidence | MODERATE |
| Percentile: future rain (+2°C) | 5.0 |
| Percentile: conversion exposure (+2°C) | 5.0 |
| Percentile: significant rain days (+2°C) | 2.7 |
| ERA5 grid location | 39.6, -105.9 — grid elevation 3405 m |
| Ski-season precip climatology | 190 mm/season across 584 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.
| Keystone Resort | |
|---|---|
| 1986-87 to 2005-06 (first half avg.) | 1.37% |
| 2006-07 to 2025-26 (second half avg.) | 1.09% |
| Observed change (half-vs-half average) | -0.27% 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 | 2829 m | -576 m | MODERATE | 2.5% | 4.6% | 7.9% | 12.5% |
| Mid | 3243 m | -162 m | GOOD | 0.5% | 1.3% | 2.6% | 4.9% |
| Summit | 3657 m | 252 m | GOOD | 0.1% | 0.2% | 0.6% | 1.4% |
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.