Bromley Mountain — 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
| Bromley Mountain | |
|---|---|
| Rain Susceptibility Score (0=low, 100=high) |
72 |
| Rain Resilience Score | 28 |
| Overall Confidence | GOOD |
| Percentile: future rain (+2°C) | 79.0 |
| Percentile: conversion exposure (+2°C) | 62.6 |
| Percentile: significant rain days (+2°C) | 76.3 |
| ERA5 grid location | 43.2, -72.9 — grid elevation 552 m |
| Ski-season precip climatology | 405 mm/season across 593 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.
| Bromley Mountain | |
|---|---|
| 1986-87 to 2005-06 (first half avg.) | 29.39% |
| 2006-07 to 2025-26 (second half avg.) | 31.30% |
| Observed change (half-vs-half average) | +1.91% 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 | 594 m | 43 m | GOOD | 36.5% | 45.1% | 54.4% | 62.9% |
| Mid | 798 m | 246 m | GOOD | 28.5% | 35.1% | 43.7% | 53.6% |
| Summit | 1001 m | 449 m | GOOD | 22.1% | 26.9% | 33.1% | 41.2% |
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.