The sailing score is Lakebrief's attempt to compress a multi-source pre-launch check into one number a sailor can read in under a second. The score is tuned for small-craft sailing — boats under roughly 25 feet, including dinghies (Sunfish, Laser, FJ, 420), small keelboats (J/22, J/24, Catalina 22), and day-sailors. Larger keelboats and powerboats will see scores that read low at conditions they'd consider perfectly fine.
Three factors are weighted into the base number, with two further modifiers applied on top. When hourly forecast data is available, the wind and gust inputs are drawn from daytime averages and peak gusts across the full sunrise-to-sunset window — not just the current-moment reading — so the score reflects the whole sailing day rather than a snapshot.
- Wind speed (40%)
- The curve plateaus at 12–15 kt sustained — the small-craft sweet spot. Dinghies are still comfortably planing through 18 kt. Below 4 kt the score drops sharply (sails won't fill meaningfully). The descent from 20 kt toward the park-rule wind limit is a smooth sigmoid rather than a cliff, so the score reflects rising risk rather than a step function. Above the park-rule limit (e.g. 21.7 kt at Spruce Run, Round Valley, and Hopatcong) the score hard-zeros, because launching is no longer legal.
- Gust risk (30%)
- The lower of two independent checks: absolute gust intensity and gust factor (peak ÷ mean). Absolute thresholds: gusts reaching 22 kt score 25/100; 25 kt or above score 0. The gust-factor branch — the meteorologically correct turbulence proxy from NOAA's Mariners' Weather Log — only engages when the mean wind is at or above 3 kt and the peak gust is at or above 17 kt. Below 17 kt, even a high ratio is normal light-air puffiness. Above those thresholds, a ratio of 1.4 scores 75, 1.6 scores 50, and 1.8+ scores 25 (convective-squall territory).
- Rain (30%)
- Driven by peak hourly precipitation intensity in the day's forecast. No rain scores 100. Light rain (under 0.1 in/hr) scores 80 — manageable but worth noting. Moderate rain (0.1–0.3 in/hr) scores 45, reflecting meaningful visibility and comfort loss. Heavy rain (0.3 in/hr or above) scores 15 — miserable conditions that significantly degrade the sailing experience. Note: rainfall intensity doesn't capture lightning risk — that's handled separately by the CAPE modifier below.
Water level is not part of the score. It operates as a separate go/no-go alert: when a lake's surface drops below its documented low-water threshold, the dashboard shows a ramp-access advisory independent of the sailing score.
Modifiers applied after the weighted sum:
- Visibility: −10 if below 5 mi, −25 if below 2 mi.
- Convective risk (CAPE): CAPE — Convective Available Potential Energy, measured in J/kg — flags thunderstorm potential that rainfall alone misses (a brief 0.05" thunderstorm carries lethal lightning; a 0.4" steady soaker doesn't). Above 1,000 J/kg the score drops by 20; above 2,500 J/kg the score is capped at 30 and the rationale flips to a stay-ashore message. PredictWind, Windy, and SailFlow all surface CAPE for the same reason.
The rationale string under the score names the dominating factor in plain English ("squally: 8 kt sustained, 20 kt gusts (factor 2.5) — hard to depower in time on a dinghy") so the number isn't a black box. The optimal-window strip identifies the longest continuous stretch of the day where wind sits in the 6–18 kt dinghy-friendly band during daylight hours.
The score is not a substitute for skipper judgment. Conditions on inland lakes can change in minutes — a thermal that ramped to 12 kt at noon can hit 22 kt by 2 PM. The optimal-window calculation tries to spot stable bands but it's a forecast, not a guarantee. Always look at the actual water before you launch.