PG1 Sitefinder

Flyability scores (1–10) ▼

9–10Excellent — Prime conditions; get to the hill

7–8Good — Solid flying day

5–6Moderate — Some flyable hours; check for hazards on arrival

3–4Marginal — Unlikely to be flyable for most pilots

1–2Not flyable — Do not fly

The headline score is the best two-hour average between 08:00–20:00 — a single good hour will not inflate it.

Hours are consecutive hours scoring 6/10 or above — often more useful than the peak score alone. The hourly dot strip in each site card shows the full picture hour by hour.

Verdict labels ▼

Good flying dayScore ≥ 7 with a reasonable window — head to the hill

Late window onlyScore ≥ 7 but good hours don't start until 16:00 or later

Brief windowScore ≥ 7 but only 1–2 consecutive good hours

Window HH:MM–HH:MM — [hazard]Score 5–6 with a flyable window, but gusts, rain, or a direction risk present — check carefully on the day

Moderate / MarginalScore 3–6, no major hazards but limited or borderline windows

Not recommendedDangerous conditions (ROTOR, too strong, severe gusts) or score ≤ 2

Warning flags ▼

ROTORWind direction creates rotor at the launch — score capped at 1. Do not fly.

DANGERWind from a sector producing rough or dangerous air — score capped at 1. Do not fly.

CAUTIONEdge of the usable wind window — score capped at 3–5. Experienced pilots only, assess carefully.

⚡ CuNimCAPE ≥ 500 J/kg — Cu-Nim storm risk. Do not fly.

⚠ TCuCAPE 300–499 J/kg — towering Cu likely, suction risk.

Blown-back riskOn-face wind ≥ 32 km/h — risk of being pushed back on launch.

Too strongMean wind ≥ 40 km/h — unsafe. Score capped at 1.

How the forecast is calculated ▼

Data comes from Open-Meteo, a free European weather model updated roughly every hour. The score is a weighted composite of five factors, then capped by hard safety rules.

Direction (45%) — Each site has defined wind windows based on the terrain. A direction only 20° off-axis can make a site unflyable due to rotor. Direction is scored as the worst of the 33ft and 262ft readings — if the ridge-height wind is cross, the score reflects that even if the surface feels on-face.

Speed (17%) — The on-face component at launch (33ft). Ideal: 12–22 km/h. Below 8 km/h at both heights = sled-ride cap (no ridge lift). Above 32 km/h = blown-back risk cap.

Gusts (11%) — Both absolute gust speed and the gust-to-mean ratio. A ratio ≥ 2.0 at high absolute speeds indicates turbulence. Sites with regular thermic cycles (Bratton, Milk Hill) suppress ratio caps in sunny on-face conditions — those gusts are thermal pulses, not rotor.

Rain (15%) — Uses actual mm/h when available; falls back to probability %. Heavy rain caps the score regardless of wind direction. Cloud cover alone does not cap the score — overcast sky has no effect on ridge lift.

Thermals (12%) — Included in the composite with a floor of 5 (neutral). Good thermals boost a ridge soaring score above what wind alone would give. Thermal quality is estimated from boundary layer height, atmospheric lapse rate, solar radiation, and CAPE.

RS wind (teal) vs TO wind (white) — Each hourly row shows two wind bar rows. RS = ridge soaring height (80m / 262ft above the launch point), what you fly in. TO = take-off height (10m / 33ft), what you feel on the ground. Both matter: the score uses whichever is worse for direction, and both are checked for speed caps.

Accuracy is good to ~3 days. The model cannot see local terrain effects — always assess conditions on arrival and trust your own judgement over any forecast.

Understanding the thermals section ▼

The Thermals accordion in a site's detail view covers XC potential — it is separate from the ridge-soaring flyability score.

↻ badges on hourly rows — appear when the per-hour thermal score is ≥ 3/10 (weak thermals detectable). The climb rate shown is an estimate based on the lapse rate, boundary layer height, and solar radiation for that hour.

Thermals from — the first hour where the model expects thermals to trigger at the surface. Requires solar radiation ≥ 100 W/m² and a thermal score ≥ 4. On overcast or rainy days, solar is too low to define a surface trigger time even if thermic mixing is happening aloft — this is why you may see thermal badges on individual hours but "No trigger today" in the accordion.

Cloud base — derived from the dew point temperature (Lifted Condensation Level). Shows as "Blue — no cumulus" only on genuinely clear low-CAPE days (CAPE < 200 J/kg and cloud cover < 60%). On overcast or rainy days the LCL is simply unavailable or irrelevant and the field shows "—".

XC potential — Low on days without a clear trigger or with high cloud cover; Good when thermals are strong, BL is deep, and cloud base is well above launch.

About ▼

About the app

PG1 Sitefinder answers one question: where should I fly today? Covers 26 sites across Wiltshire, Gloucestershire, Somerset, and South-East Wales (SEWPG + Brecon Beacons). Each site is scored hour by hour on wind direction, speed, gusts, and rain — so the best option for today's conditions is always at the top. Made for club members by a club member.

Community

Get forecasts, discuss conditions, share flying reports, and flag scoring issues with other pilots.

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Feedback & bug reports

Found a score that didn't match conditions on the day? Post in the Telegram group with the site, date, and what you observed on arrival — that's the most useful feedback.

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Release history

Version: —

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About Ninthstone

PG1 Sitefinder is made by Ninthstone Ltd, a small software company based in the UK.

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