The day on the hill
Frequent summit cloud on Carnedd Llewelyn: summit wind broadly 5-20 mph, with gusts 15-25 mph at times (a moderate breeze).
Cloud & views
Cloud base mostly around 600–900 m through daylight. Summit cloud is likely, but brief clear spells remain possible if the cloud sits higher than expected.
Cloud-height uncertainty could put the summit in or out of cloud. Clear spells may be difficult to time.
Any sunshine may be confined to lower ground or breaks away from the summit.
Rain & temperature
The ground is likely to be wet after recent rain. Little or no rain is forecast.
Forecast confidence
Cloud height remains uncertain, especially where it is close to summit level. Cloud-height uncertainty could put the summit in or out of cloud, even where forecasts agree on the wider cloud cover.
Sunshine context Model-grid estimate, not summit sunshine
The surrounding model grid indicates 5.9 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.
Cloud may obscure this summit even while the surrounding model grid indicates sunshine. The low cloud-free summit estimate is a reason to be cautious about expecting views.
- Early
- 0 h
- Midday
- 2 h
- Later
- 2.9 h
Overnight forecast: 17:00–08:00 (UK local time), in Wild camping below.
Overnight · 17:00–08:00Wild campingBetaCondensation risk is high near 300, 600 and 900 m. 64/100Mixed · 600 m View detailsHide details
Full overnight outlook
Open-hillside camping looks reasonable overall around 600 m (64/100). Light winds are expected on open ground, though local shelter and exposure still matter. 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. Condensation risk is high near 300, 600 and 900 m. Ventilation will matter.
Moon overnight
Waxing gibbous moon
- Illuminated disc
- 78%
- Moonrise
- 17:40 BST
- Moonset
- 01:30 next morning BST
Clear spells may allow a view of the Moon. Illumination describes the sunlit part of the Moon, not brightness at your pitch.
Overnight window: 21 Sep, 17:00 BST to 22 Sep, 08:00 BST. Approximate open-horizon times; hills can hide the Moon. Still take a headtorch.
Elevation reference (open ground)
- Wind / gust
- 4 mph / 11 mph
- Typical / low
- 14.3°C / 12.7°C
- In cloud
- 0% of modelled night
- Condensation
- High
- Wind / gust
- 4 mph / 13 mph
- Typical / low
- 14.3°C / 12.7°C
- In cloud
- 0% of modelled night
- Condensation
- High
- Wind / gust
- 5 mph / 15 mph
- Typical / low
- 13.1°C / 11.6°C
- In cloud
- 100% of modelled night
- Condensation
- High
Warmth planning: As a broad starting point, consider a 2-season bag with an ISO/EN comfort rating at or below about 10°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 & scramblingBetaRock may be damp or still drying. Mixed56/100 View detailsHide details
Full climbing & scrambling outlook
Conditions for exposed scrambling look mixed (56/100). Recent rain may leave seepage and damp rock, especially on shaded sections. The mapped summit rock is Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks (Foel Fras Volcanic Complex). Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery. Representative samples along available mapped routes also include Basalt, Felsic tuff and 4 other mapped types, so rock character and wet-weather behaviour may change across the mountain. Cloud may also make route-finding and retreat harder.
Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them 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.
Carneddau Aber Falls
volcanic rock
Carneddau Ogwen
volcanic rock, slate or mudstone, sandstone or gritstone
Geological detail and BGS records
7 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.
Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.
BGS recordOften grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.
BGS recordOften grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.
BGS recordOften positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.
BGS recordOften grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.
BGS recordOften grippy when dry, but wet sandstone can lose strength and may be damaged by climbing. Avoid it while saturated and allow shaded walls, pockets and seepage lines time to dry.
BGS recordOften positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.
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 darkBetaClearer spells are possible, but other forecasts keep much of the sky obscured by cloud. View forecastClose forecast
After dark: aurora and stargazing
Night beginning 2026-09-21. All times are UK local time.
Stargazing
Mixed sky conditions during the best available spell: 22 Sep, 01:00 BST to 02:00 BST.
Clearer spells are possible, but other forecasts keep much of the sky obscured by cloud.
Moon-free dark sky: 22 Sep, 01:20 BST to 05:05 BST.
Sky conditions through the night
| Time | Viewing conditions |
|---|---|
| 21 Sep, 21:15 BST to 22:00 BST | Mixed sky conditions Forecasts disagree on rain or visibility, so viewing conditions could be poorer than the clearer outlook suggests. Forecast models disagree. |
| 21 Sep, 22:00 BST to 23:00 BST | Mixed sky conditions Clearer spells are possible, but other forecasts keep much of the sky obscured by cloud. Forecast models disagree. |
| 21 Sep, 23:00 BST to 22 Sep, 00:00 BST | Mixed sky conditions Clearer spells are possible, but other forecasts keep much of the sky obscured by cloud. Forecast models disagree. |
| 22 Sep, 00:00 BST to 01:00 BST | Mixed sky conditions Clearer spells are possible, but other forecasts keep much of the sky obscured by cloud. Forecast models disagree. |
| 22 Sep, 01:00 BST to 02:00 BST | Mixed sky conditions Clearer spells are possible, but other forecasts keep much of the sky obscured by cloud. Forecast models disagree. |
| 22 Sep, 02:00 BST to 03:00 BST | Mixed sky conditions Clearer spells are possible, but other forecasts keep much of the sky obscured by cloud. Forecast models disagree. |
| 22 Sep, 03:00 BST to 04:00 BST | Mixed sky conditions Clearer spells are possible, but other forecasts keep much of the sky obscured by cloud. Forecast models disagree. |
| 22 Sep, 04:00 BST to 05:00 BST | Mixed sky conditions Clearer spells are possible, but other forecasts keep much of the sky obscured by cloud. Forecast models disagree. |
| 22 Sep, 05:00 BST to 05:05 BST | Mixed sky conditions Clearer spells are possible, but other forecasts keep much of the sky obscured by cloud. Forecast models disagree. |
Moon, darkness and meteor showers
Gibbous moon, about 78% illuminated.
Moonrise around 21 Sep, 17:45 BST.
Moonset around 22 Sep, 01:20 BST.
Full darkness: 21 Sep, 21:15 BST to 22 Sep, 05:05 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 879 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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