The day on the hill
Strong gusts on The Cairnwell: summit wind broadly 25-45 mph, with gusts 55-65 mph at times (gale-force mean winds at times).
Wind & exposure
Much calmer lower down - generally 15-25 mph in the valley, rising towards the tops.
Cloud & views
Cloud base around 900–1200 m in the morning, lifting to 1500–1800 m around midday. The summit is likely to stay mostly clear.
Cloud-height uncertainty could put the summit in or out of cloud. Clear spells may be difficult to time.
Cloud may hang lower on northwestern slopes and lift somewhat on the southeastern side, but local terrain can differ.
Rain & temperature
Little or no rain is forecast. Cold on exposed tops: air temperature broadly 2 to 6°C, feeling around -6 to -2°C in the wind.
Forecast models differ on summit wind strength: around 39-46 mph at walker height, with gusts 55-64 mph.
Forecast confidence
Cloud height remains uncertain, especially where it is close to summit level. Keep windproof and warm layers readily available.
Walking into the wind is likely to be arduous, with buffeting that can knock you off balance. Cloud-height uncertainty could put the summit in or out of cloud, even where forecasts agree on the wider cloud cover.
Cloud-free timing: Around 55% early, improving to around 90% later.
Sunshine context Model-grid estimate, not summit sunshine
The surrounding model grid indicates 6.1 h of sunshine. This is not a forecast of time in sunshine on the summit. Use the cloud and views outlook above for the conditions on this mountain.
- Early
- 1.3 h
- Midday
- 2.7 h
- Later
- Less than 1 hour
Overnight forecast: 17:00–08:00 (UK local time), in Wild camping below.
Overnight · 17:00–08:00Wild campingBetaGusts near 40 mph make meaningful shelter important. 59/100Mixed · 600 m View detailsHide details
Full overnight outlook
Open-hillside camping looks mixed overall around 600 m (59/100). A lower pitch near 300 m looks more comfortable. Conditions are less suitable by 900 m. Open-ground gusts may reach about 40 mph. Seek meaningful shelter. Peak gusts range from about 25 mph at 300 m to 40 mph at 900 m. Little overnight rain is forecast. Pitches near 900 m may spend part of the night in cloud, bringing damp conditions and poor visibility while cloud is present.
Moon overnight
Waxing gibbous moon
- Illuminated disc
- 70%
- Moonrise
- 17:45 BST
- Moonset
- 23:41 BST
Extensive cloud may limit moonlight. Illumination describes the sunlit part of the Moon, not brightness at your pitch.
Overnight window: 20 Sep, 17:00 BST to 21 Sep, 08:00 BST. Approximate open-horizon times; hills can hide the Moon. Still take a headtorch.
Elevation reference (open ground)
- Wind / gust
- 14 mph / 27 mph
- Typical / low
- 7.8°C / 6.6°C · much of the night
- In cloud
- 0% of modelled night
- Condensation
- Low
- Wind / gust
- 16 mph / 33 mph
- Typical / low
- 7.8°C / 6.6°C · much of the night
- In cloud
- 0% of modelled night
- Condensation
- Low
- Wind / gust
- 19 mph / 39 mph
- Typical / low
- 6.0°C / 5.2°C · much of the night
- In cloud
- 27% of modelled night
- Condensation
- Low
Warmth planning: As a broad starting point, consider a 3-season bag with an ISO/EN comfort rating at or below about 4°C. Allow more margin if you sleep cold or expect fatigue, and use an adequate insulated mat. Dampness is possible, so keep the sleep system dry and ensure its insulation remains effective if damp.
Open-hillside reference. A sheltered pitch may be calmer; cols and ridges may be much windier. Tent design and the exact pitch still matter. Read about sleeping-bag comfort ratings, pitching in strong winds or using the wild-camping forecast.
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Daytime · exposed rockClimbing & scramblingBetaGusts near 55 mph may affect balance on exposed rock. Poor20/100 View detailsHide details
Full climbing & scrambling outlook
Conditions for exposed scrambling look poor (20/100). Rock is likely to be mostly dry, though seepage and shaded holds are not resolved. The mapped summit rock is Pebbly quartzite (An Socach Quartzite Formation). Usually hard and grippy when dry and often reasonably positive when damp, although wet lichen and smooth slabs can still be slippery. Representative samples along available mapped routes also include Granite, Graphitic pelite, marble and psammite and 1 other mapped type, so rock character and wet-weather behaviour may change across the mountain. Gusts may reach about 55 mph. Crosswinds can make exposed ridges substantially more serious.
Usually hard and grippy when dry and often reasonably positive when damp, although wet lichen and smooth slabs can still be slippery. Summit-point mapping plus representative BGS bedrock samples along available GPX routes. These are not continuous geological surveys; contacts, superficial deposits and the exposed rock on individual holds may differ.
Rock groups along the sampled routes
These are mapped rock groups, not separate weather forecasts or a ranking of route safety.
Càrn Aosda, Càrn a' Ghèoidh and The Cairnwell
quartzite, granite, gneiss or gabbro, psammite, pelite or semipelite
Geological detail and BGS records
4 rock types appear across the available route samples
The summit type remains the forecast's cautious rock-response reference. Other mapped types show where conditions may behave differently elsewhere on the mountain.
Usually hard and grippy when dry and often reasonably positive when damp, although wet lichen and smooth slabs can still be slippery.
BGS recordGenerally grippy when dry and often still positive when damp, but wet slabs, lichen, polish and drainage lines can remain slippery.
BGS recordDry quartz-rich bands can be grippy, while mica-rich or foliated sections, lichen and vegetation may become slippery when wet.
BGS recordGenerally grippy when dry and often still positive when damp, but wet slabs, lichen, polish and drainage lines can remain slippery.
BGS recordGeneric exposed scrambling terrain; mapped summit-point bedrock is included where available, but route grade, exact rock, polish, drainage and escape options remain unresolved. Contains British Geological Survey materials © UKRI 2026. How to use the climbing and scrambling forecast.
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Overnight · Aurora, stars & meteorsAfter darkBetaCloud is likely to obscure much of the sky. Rain may interrupt viewing. View forecastClose forecast
After dark: aurora and stargazing
Night beginning 2026-09-20. All times are UK local time.
Stargazing
Poor sky conditions during the best available spell: 21 Sep, 04:00 BST to 04:45 BST.
Cloud is likely to obscure much of the sky. Rain may interrupt viewing.
Moon-free dark sky: 20 Sep, 23:30 BST to 21 Sep, 04:45 BST.
Sky conditions through the night
| Time | Viewing conditions |
|---|---|
| 20 Sep, 21:30 BST to 22:00 BST | Poor sky conditions Cloud is likely to obscure much of the sky. |
| 20 Sep, 22:00 BST to 23:00 BST | Poor sky conditions Cloud is likely to obscure much of the sky. |
| 20 Sep, 23:00 BST to 21 Sep, 00:00 BST | Poor sky conditions Cloud is likely to obscure much of the sky. |
| 21 Sep, 00:00 BST to 01:00 BST | Poor sky conditions Cloud is likely to obscure much of the sky. |
| 21 Sep, 01:00 BST to 02:00 BST | Poor sky conditions Cloud is likely to obscure much of the sky. |
| 21 Sep, 02:00 BST to 03:00 BST | Poor sky conditions Cloud is likely to obscure much of the sky. |
| 21 Sep, 03:00 BST to 04:00 BST | Poor sky conditions Cloud is likely to obscure much of the sky. |
| 21 Sep, 04:00 BST to 04:45 BST | Poor sky conditions Cloud is likely to obscure much of the sky. Rain may interrupt viewing. |
Moon, darkness and meteor showers
Gibbous moon, about 69% illuminated.
Moonrise around 20 Sep, 17:50 BST.
Moonset around 20 Sep, 23:30 BST.
Full darkness: 20 Sep, 21:30 BST to 21 Sep, 04:45 BST.
Moon times assume an open horizon. Hills can hide the Moon sooner. Moon-free does not mean cloud-free.
Southern Taurids are active on this night. Activity may be much lower away from the peak.
- Draconids: peak around 9 October 2026.
- Southern Taurids: peak around 10 October 2026.
- Orionids: peak around 21 October 2026.
- Northern Taurids: peak around 12 November 2026.
- Leonids: peak around 18 November 2026.
- Geminids: peak around 14 December 2026.
- Ursids: peak around 22 December 2026.
Dates from the Royal Observatory Greenwich. Activity dates do not guarantee visible meteors. Look across a broad, dark sky, not only north.
Darkness of the surroundings
Estimated darkness rank 370 of 980 assessed peaks (1 is darkest), based on surrounding artificial light in 2021. This is not a measurement of tonight’s sky.
2021 artificial-light baseline, not measured sky brightness or a Bortle class. Changes to lighting, blue-rich LEDs, terrain screening, atmospheric scattering and cloud-reflected light are not resolved. Similar ranks are not meaningfully distinct. Darkness is not a recommendation to climb a summit at night.
VIIRS nighttime lights: Earth Observation Group, Payne Institute for Public Policy, Colorado School of Mines. Reprocessed by OpenGeoHub/OpenLandMap. Cropped and ranked by Mountain Weather.
Sky-weather grades exclude light pollution, terrain and thin haze. They are not mountain safety ratings. Check the mountain and camping forecast separately. Accessible lower viewpoints may be a better choice than summits.
Recommended kit for this dayWeather-aware packing prompts, plus your core hillwalking kitView kit
For a day hillwalk, not a complete route-specific checklist. Carry navigation and backup you can use, warm and waterproof layers, suitable footwear, food and water, a headtorch, emergency shelter, first aid and a way to call for help. Snow, ice, technical terrain and overnight trips need additional equipment and skills.
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