Thacka Beck Reservoir · NW

1 · The sailing score (0–10)

Every forecast hour starts from the steady wind measured against the chosen profile’s comfort band. On the default “Cruising dinghy” profile, 6–16 knots scores the full 10. Below 3 knots there isn’t enough wind to sail (score 1); from 3 to 6 the score climbs. Above 16 knots it declines gently at first (to 22), then steeply towards 30 — the limit for small craft. Beginner · Kayak, Cruising dinghy and Performance · Wing run the same maths with shifted bands; the profile picker in the dashboard above applies site-wide.

2 · Subtracted from the wind score

• Gusts: gusts beyond 1.5× the steady wind cost up to 2.5 points; gusts past 25 knots a flat 1.5 on top.
• Rain: from 70% probability or 1.5 mm/h, 4 points come off; from 45% or 0.3 mm/h, 1.5 — storm risk outweighs a bit of wet.
• Cold: below 13 °C costs 1.5 points, below 4 °C costs 2.5 — capsize risk follows the water temperature, estimated from air temperature because this lake has no sensor.

Final value = wind score minus penalties, clamped to 0–10 at one decimal. It drives the traffic-light colours and the go / caution / no-go verdict.

3 · Day cards & best windows

A day’s score is the average across daylight hours 7–19 — night hours don’t count. “Best windows” are runs of at least two consecutive daylight hours scoring 6 or better, sorted by average score, four at most. A window ending at 14:00 means the score drops below 6 from 14:00 onwards.

4 · Water level & temperature

Water level reports every 15 minutes, the raw station reading in metres above the station datum — not a percentage-full figure like a reservoir. Compare it with the 7-day curve on the water page and you can see at a glance whether the lake is running high or low.

Wind, gusts, rain and air temperature come from the Open-Meteo forecast for the lake’s coordinates — real shorelines (offshore gusts, valley funnels) can diverge from the model.