Carnedd Llewelyn Weather Forecast – 1,064m, Eryri (Snowdonia)

Thursday 3 September 2026Medium confidence

Overall hill weather22/100Poor

Wind34 mph W Gusts47 mph Feels5°C Rain0.9 mm Cloud-free summit35% Cloud base through day1,000–1,300 m Freezing levelAbove summit Daylight06:28–20:01 · 13.6 h

Forecast confidence: Rain timing may shift by several hours, which could change how much of the main walking period stays dry.

Severe spate risk

Burns and unbridged crossings may rise quickly. Assess them at the water and turn back if unsure.

A rough, clagged-in day on Carnedd Llewelyn: summit wind broadly 25-40 mph, with gusts 40-50 mph during the evening (gale-force winds). Severe spate risk based on forecast rainfall. Burns and unbridged crossings may become unsafe or impassable. Most likely from around 00:00 until around 06:00 the following day. Much calmer lower down - generally 15-25 mph in the valley, rising towards the tops. Cloud base mostly around 1000–1300 m through daylight. Expect the top to stay in cloud for most or all of daylight, with no dependable break. Cloud height is close to summit level at times, so small local changes could put the top in or out of cloud. Cloud is likely to hang lowest on western slopes; the eastern side should see somewhat higher bases and better breaks. Very little direct sunshine is indicated; cloud is likely to remain extensive. Little or no rain expected. Confidence moderate (forecast models agree on the walking impact of the wind) - walker-height summit wind could reasonably be 29-37 mph, with gusts 41-52 mph. Cloud base is the least certain part of this - it could sit a couple of hundred metres either way, especially where it is close to summit level.

At this mountain

Sunshine and sky

Extensive cloud. Cloud is likely to remain extensive for much of the day.

Modelled sunshine0 h0% of daylight

Early0 h sunshine

Midday0 h sunshine

Later0 h sunshine

These are direct modelled sunshine hours during daylight, not the probability of sunshine. Cloud cover and summit cloud are assessed separately in the forecast above. Local hill cloud can still make an individual summit brighter or duller than the surrounding model grid.

Morning · 07:00–13:00Poor

28/100

Afternoon & evening · 13:00–22:00Poor

15/100

Separate hill-weather grades help compare an early start with later conditions; the main daytime forecast above still covers the core walking day.

Overnight · 6 p.m.–9 a.m.Wild campingBetaGusts near 50 mph make meaningful shelter important. 39/100Poor · 600 m View detailsHide details

Night beginning Thursday 3 September 2026

Full overnight outlook

Open-hillside camping looks poor overall around 600 m (39/100). Open-ground gusts may reach about 50 mph, making exposed pitches a poor choice. Peak gusts increase from about 35 mph at 300 m to 50 mph at 900 m. A wet night is likely, with roughly 59.8 mm and rain liable to affect both pitching and packing up. Condensation risk is high across the modelled levels, so a wet pack-up is possible; ventilation will matter. The coldest temperature falls from about 10.4°C at 300 m to 8°C at 900 m.

Overnight rain60 mm Open ground · 600 m25 mph · gusts 44 mph Morning pack-upDampness possible Sleeping-bag warmthISO comfort rating about 6°C or lower

Elevation reference (open ground)

300 m39/100 · poor

Wind / gust: 21 / 37 mph
Typical / low: 13.4° / 10.4°C
In cloud: Unlikely
Condensation: High

600 m39/100 · poor

Wind / gust: 25 / 44 mph
Typical / low: 12.9° / 9.9°C · a brief spell
In cloud: Unlikely
Condensation: High

900 m39/100 · poor

Wind / gust: 29 / 52 mph
Typical / low: 11.0° / 8.0°C · several hours
In cloud: Unlikely
Condensation: High

Warmth planning: As a broad starting point, consider a 3-season bag with an ISO/EN comfort rating at or below about 6°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 40 mph increase the seriousness of exposed ground. 0/100Poor · Very poor View detailsHide details

Generic exposed-rock guidance

Full climbing & scrambling outlook

Conditions for exposed scrambling look very poor (0/100). Rain during the useful part of the day is likely to leave rock wet and more slippery. 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. Gusts may reach about 40 mph; crosswinds can make exposed ridges substantially more serious. Cloud may also make route-finding and retreat harder.

Rock surfaceWet rock likelyPeak gust42 mphRain0.7 mm

Main factorsgusts around 40 mphwet rock likelymuch of the route may be in cloud

Mapped rock across the summit and available routes Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks Foel Fras Volcanic Complex

Origin: Sedimentary and igneous
Rock family: Volcanic rock
Mapping: BGS Geology 50K · 1:50,000
Rock-response profile: Low confidence

View the summit BGS record

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.

Mapped variation

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.

Summit mapping Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks Foel Fras Volcanic Complex Around 1,048 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Basalt Foel Grach Basalt Formation 932–1,053 m samples Seen on Peak Carneddau Aber Falls

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Felsic tuff Capel Curig Volcanic Formation Around 680 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Mudstone and siltstone Cwm Eigiau Formation Around 767 m Seen on Peak Carneddau Ogwen

Often positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.

BGS record

Route sample Rhyolite Unnamed Igneous Intrusion, Ordovician Around 488 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Sandstone Llewelyn Volcanic Group Around 955 m Seen on Peak Carneddau Ogwen

Often 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 record

Route sample Siltstone Capel Curig Volcanic Formation Around 580 m Seen on Peak Carneddau Ogwen

Often positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.

BGS record

See sampled routes

Peak Carneddau Aber Falls932–1,053 m samplesBasalt

Peak Carneddau Ogwen488–1,048 m samplesFelsic tuff · Mudstone and siltstone · Rhyolite · Sandstone · Siltstone · Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks

Generic 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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Friday 4 September 2026Medium confidence

Overall hill weather18/100Poor

Wind32 mph W Gusts44 mph Feels2°C Rain4.9 mm Cloud-free summit25% Cloud base through day700–1,300 m Freezing levelAbove summit Daylight06:30–19:58 · 13.5 h

Forecast confidence: Cloud height is close to summit level at times, so small local changes could put the top in or out of cloud.

Severe spate risk

Burns and unbridged crossings may rise quickly. Assess them at the water and turn back if unsure.

A grey, cloudy day on Carnedd Llewelyn: summit wind broadly 25-35 mph, with gusts 40-50 mph during the morning (gale-force winds). The ground is likely to be wet after recent rain. Severe spate risk based on forecast rainfall. Burns and unbridged crossings may become unsafe or impassable. Most likely from around 00:00 until around 16:00. Cloud base around 1000-1300 m in the morning, lowering to 700-1000 m around midday. Expect the top to stay in cloud for most or all of daylight, with no dependable break. Cloud height is close to summit level at times, so small local changes could put the top in or out of cloud. Cloud is likely to hang lowest on western slopes; the eastern side should see somewhat higher bases and better breaks. Very little direct sunshine is indicated; cloud is likely to remain extensive. Some rain is likely, with around 2-5 mm indicated; timing and local totals remain uncertain. Cold on top: air temperature broadly 6 to 10°C, feeling around 0 to 4°C in the wind - wrap up. Cloud base is the least certain part of this - it could sit a couple of hundred metres either way, especially where it is close to summit level.

At this mountain

Sunshine and sky

Extensive cloud. Cloud is likely to remain extensive for much of the day.

Modelled sunshineLess than 1 hour4% of daylight

Early0 h sunshine

Midday0 h sunshine

LaterLess than 1 hour sunshine

These are direct modelled sunshine hours during daylight, not the probability of sunshine. Cloud cover and summit cloud are assessed separately in the forecast above. Local hill cloud can still make an individual summit brighter or duller than the surrounding model grid.

Morning · 07:00–13:00Poor

13/100

Afternoon & evening · 13:00–22:00Poor

22/100

Separate hill-weather grades help compare an early start with later conditions; the main daytime forecast above still covers the core walking day.

Overnight · 6 p.m.–9 a.m.Wild campingBetaGusts near 45 mph make meaningful shelter important. 64/100Mixed · 600 m View detailsHide details

Night beginning Friday 4 September 2026

Full overnight outlook

Open-hillside camping looks reasonable overall around 600 m (64/100). A lower pitch near 300 m looks more comfortable; conditions are less suitable by 900 m. Open-ground gusts may reach about 45 mph, making exposed pitches a poor choice. Peak gusts increase from about 30 mph at 300 m to 45 mph at 900 m. Little overnight rain is expected. From around 600 m upward, pitches may spend part of the night in cloud, with high condensation risk, persistent damp and poor visibility; ventilation will matter. The coldest temperature falls from about 8.4°C at 300 m to 6.5°C at 900 m.

Overnight rain0.1 mm Open ground · 600 m23 mph · gusts 38 mph Morning pack-upDampness possible Sleeping-bag warmthISO comfort rating about 6°C or lower

Elevation reference (open ground)

300 m64/100 · reasonable

Wind / gust: 19 / 32 mph
Typical / low: 9.2° / 8.4°C · much of the night
In cloud: Unlikely
Condensation: High

600 m64/100 · reasonable

Wind / gust: 23 / 38 mph
Typical / low: 9.1° / 8.4°C · much of the night
In cloud: 25% of night
Condensation: High

900 m39/100 · poor

Wind / gust: 26 / 45 mph
Typical / low: 7.2° / 6.5°C · much of the night
In cloud: 38% of night
Condensation: High

Warmth planning: As a broad starting point, consider a 3-season bag with an ISO/EN comfort rating at or below about 6°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.

Did this match your night?Share a quick observation to help improve this beta forecast.Give feedback

Daytime · exposed rockClimbing & scramblingBetaGusts near 45 mph increase the seriousness of exposed ground. 0/100Poor · Very poor View detailsHide details

Generic exposed-rock guidance

Full climbing & scrambling outlook

Conditions for exposed scrambling look very poor (0/100). Rain during the useful part of the day is likely to leave rock wet and more slippery. 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. Gusts may reach about 45 mph; crosswinds can make exposed ridges substantially more serious. Cloud may also make route-finding and retreat harder.

Rock surfaceWet rock likelyPeak gust44 mphRain4.8 mm

Main factorsgusts around 45 mphwet rock likelymuch of the route may be in cloud

Mapped rock across the summit and available routes Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks Foel Fras Volcanic Complex

Origin: Sedimentary and igneous
Rock family: Volcanic rock
Mapping: BGS Geology 50K · 1:50,000
Rock-response profile: Low confidence

View the summit BGS record

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.

Mapped variation

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.

Summit mapping Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks Foel Fras Volcanic Complex Around 1,048 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Basalt Foel Grach Basalt Formation 932–1,053 m samples Seen on Peak Carneddau Aber Falls

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Felsic tuff Capel Curig Volcanic Formation Around 680 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Mudstone and siltstone Cwm Eigiau Formation Around 767 m Seen on Peak Carneddau Ogwen

Often positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.

BGS record

Route sample Rhyolite Unnamed Igneous Intrusion, Ordovician Around 488 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Sandstone Llewelyn Volcanic Group Around 955 m Seen on Peak Carneddau Ogwen

Often 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 record

Route sample Siltstone Capel Curig Volcanic Formation Around 580 m Seen on Peak Carneddau Ogwen

Often positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.

BGS record

See sampled routes

Peak Carneddau Aber Falls932–1,053 m samplesBasalt

Peak Carneddau Ogwen488–1,048 m samplesFelsic tuff · Mudstone and siltstone · Rhyolite · Sandstone · Siltstone · Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks

Generic 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.

Did this match your experience?Tell us about the rock surface and wind to help improve this beta forecast.Give feedback

Saturday 5 September 2026Medium confidence

Overall hill weather72/100Good

Wind21 mph W Gusts29 mph Feels0°C Rain0.0 mm Cloud-free summit40% Cloud base through day600–1,300 m Freezing levelAbove summit Daylight06:31–19:56 · 13.4 h

Forecast confidence: Cloud height is close to summit level at times, so small local changes could put the top in or out of cloud.

Cloud-free timing: Best around midday at about 70%; around 30% early and 30% later.

A grey, cloudy day on Carnedd Llewelyn: summit wind broadly 15-25 mph, with gusts 25-35 mph early in the morning (fresh and blowy). The ground is likely to be saturated after recent rain. Expect boggy paths and rapid runoff if more rain arrives. Cloud base around 600–900 m in the morning, then around 1000–1300 m around midday and 800–1100 m by late afternoon. The top is likely to drift in and out of cloud, with the best chance of a view from the morning into the afternoon. Cloud height is close to summit level at times, so small local changes could put the top in or out of cloud. about 6 hours of sunshine is indicated, with variable cloud giving brighter and duller spells. Little or no rain expected. Cold on top: air temperature broadly 4 to 8°C, feeling around -2 to 2°C in the wind - wrap up. Cloud base is the least certain part of this - it could sit a couple of hundred metres either way, especially where it is close to summit level.

At this mountain

Sunshine and sky

Brighter and duller spells. Expect alternating brighter and duller spells.

Modelled sunshine5.5 h42% of daylight

EarlyLess than 1 hour sunshine

Midday3.5 h sunshine

LaterLess than 1 hour sunshine

These are direct modelled sunshine hours during daylight, not the probability of sunshine. Cloud cover and summit cloud are assessed separately in the forecast above. Local hill cloud can still make an individual summit brighter or duller than the surrounding model grid.

Morning · 07:00–13:00Good

73/100

Afternoon & evening · 13:00–22:00Good

71/100

Separate hill-weather grades help compare an early start with later conditions; the main daytime forecast above still covers the core walking day.

Overnight · 6 p.m.–9 a.m.Wild campingBetaGusts near 50 mph make meaningful shelter important. 77/100Good · 600 m View detailsHide details

Night beginning Saturday 5 September 2026

Full overnight outlook

Open-hillside camping looks promising overall around 600 m (77/100). A lower pitch near 300 m looks more comfortable; conditions are less suitable by 900 m. Open-ground gusts may reach about 50 mph, making exposed pitches a poor choice. Peak gusts increase from about 35 mph at 300 m to 50 mph at 900 m. Wind may shift from westerly to southerly; shelter that works at dusk may be less effective later. Little overnight rain is expected. From around 900 m upward, pitches may spend part of the night in cloud, bringing persistent damp and poor visibility. The coldest temperature falls from about 10.5°C at 300 m to 8.8°C at 900 m.

Overnight rain0.0 mm Open ground · 600 m18 mph · gusts 44 mph Morning pack-upNo wet signal Sleeping-bag warmthISO comfort rating about 8°C or lower

Elevation reference (open ground)

300 m81/100 · promising

Wind / gust: 15 / 36 mph
Typical / low: 13.4° / 10.5°C
In cloud: Unlikely
Condensation: Low

600 m77/100 · promising

Wind / gust: 18 / 44 mph
Typical / low: 13.4° / 10.5°C
In cloud: Unlikely
Condensation: Low

900 m39/100 · poor

Wind / gust: 21 / 51 mph
Typical / low: 14.2° / 8.8°C · a brief spell
In cloud: 38% of night
Condensation: Low

Warmth planning: As a broad starting point, consider a 2-season bag with an ISO/EN comfort rating at or below about 8°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.

The ground is likely to be very wet after recent rain; expect boggy approaches and choose a durable pitch carefully.

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.

Did this match your night?Share a quick observation to help improve this beta forecast.Give feedback

Daytime · exposed rockClimbing & scramblingBetaRock may be damp or still drying after recent rain. 62/100Mixed · Fair View detailsHide details

Generic exposed-rock guidance

Full climbing & scrambling outlook

Conditions for exposed scrambling look fair (62/100). Some rock may still be damp or drying; polished slabs and vegetated sections could be notably worse. 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.

Rock surfaceDamp or dryingPeak gust28 mphRain0.0 mm

Main factorsdamp or incompletely dried rock possiblemuch of the route may be in cloud

Mapped rock across the summit and available routes Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks Foel Fras Volcanic Complex

Origin: Sedimentary and igneous
Rock family: Volcanic rock
Mapping: BGS Geology 50K · 1:50,000
Rock-response profile: Low confidence

View the summit BGS record

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.

Mapped variation

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.

Summit mapping Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks Foel Fras Volcanic Complex Around 1,048 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Basalt Foel Grach Basalt Formation 932–1,053 m samples Seen on Peak Carneddau Aber Falls

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Felsic tuff Capel Curig Volcanic Formation Around 680 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Mudstone and siltstone Cwm Eigiau Formation Around 767 m Seen on Peak Carneddau Ogwen

Often positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.

BGS record

Route sample Rhyolite Unnamed Igneous Intrusion, Ordovician Around 488 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Sandstone Llewelyn Volcanic Group Around 955 m Seen on Peak Carneddau Ogwen

Often 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 record

Route sample Siltstone Capel Curig Volcanic Formation Around 580 m Seen on Peak Carneddau Ogwen

Often positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.

BGS record

See sampled routes

Peak Carneddau Aber Falls932–1,053 m samplesBasalt

Peak Carneddau Ogwen488–1,048 m samplesFelsic tuff · Mudstone and siltstone · Rhyolite · Sandstone · Siltstone · Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks

Generic 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.

Did this match your experience?Tell us about the rock surface and wind to help improve this beta forecast.Give feedback

Sunday 6 September 2026Medium confidence

Overall hill weather56/100Mixed

Wind41 mph SW Gusts58 mph Feels4°C Rain0.9 mm Cloud-free summit60% Cloud base through day500–2,300 m Freezing levelAbove summit Daylight06:33–19:54 · 13.3 h

Forecast confidence: Summit wind could be roughly 35-50 mph, which changes how difficult exposed walking may feel.

Cloud-free timing: Around 70% early, falling to around 40% later.

A wild day on Carnedd Llewelyn: summit wind broadly 30-45 mph, with gusts 55-65 mph around midday (storm-force winds). The ground is likely to be saturated after recent rain. Expect boggy paths and rapid runoff if more rain arrives. Much calmer lower down - generally 15-25 mph in the valley, rising towards the tops. A generally bright day is indicated, with about 12 hours of sunshine. Little or no rain expected. Confidence moderate (Summit wind could be roughly 35-50 mph, which changes how difficult exposed walking may feel) - walker-height summit wind could reasonably be 35-50 mph, with gusts 49-70 mph. Cloud base is the least certain part of this - it could sit a couple of hundred metres either way, especially where it is close to summit level.

At this mountain

Sunshine and sky

Generally bright. A generally bright day is indicated.

Modelled sunshine12 h92% of daylight

Early2 h sunshine

Midday4 h sunshine

Later4 h sunshine

These are direct modelled sunshine hours during daylight, not the probability of sunshine. Cloud cover and summit cloud are assessed separately in the forecast above. Local hill cloud can still make an individual summit brighter or duller than the surrounding model grid.

Morning · 07:00–13:00Mixed

62/100

Afternoon & evening · 13:00–22:00Mixed

51/100

Separate hill-weather grades help compare an early start with later conditions; the main daytime forecast above still covers the core walking day.

Overnight · 6 p.m.–9 a.m.Wild campingBetaGusts near 50 mph make meaningful shelter important. 69/100Mixed · 600 m View detailsHide details

Night beginning Sunday 6 September 2026

Full overnight outlook

Open-hillside camping looks reasonable overall around 600 m (69/100). A lower pitch near 300 m looks more comfortable; conditions are less suitable by 900 m. Open-ground gusts may reach about 50 mph, making exposed pitches a poor choice. Peak gusts increase from about 35 mph at 300 m to 50 mph at 900 m. Around 2.7 mm is forecast, with a damp or wet pitch most likely. From around 600 m upward, pitches may spend part of the night in cloud, bringing persistent damp and poor visibility. The coldest temperature falls from about 10.1°C at 300 m to 7.8°C at 900 m.

Overnight rain2.7 mm Open ground · 600 m22 mph · gusts 41 mph Morning pack-upDampness possible Sleeping-bag warmthISO comfort rating about 6°C or lower

Elevation reference (open ground)

300 m70/100 · reasonable

Wind / gust: 18 / 34 mph
Typical / low: 11.2° / 10.1°C
In cloud: Unlikely
Condensation: Moderate

600 m69/100 · reasonable

Wind / gust: 22 / 41 mph
Typical / low: 10.8° / 9.9°C · a brief spell
In cloud: 31% of night
Condensation: Moderate

900 m39/100 · poor

Wind / gust: 26 / 48 mph
Typical / low: 8.6° / 7.8°C · much of the night
In cloud: 38% of night
Condensation: Moderate

Warmth planning: As a broad starting point, consider a 3-season bag with an ISO/EN comfort rating at or below about 6°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.

The ground is likely to be very wet after recent rain; expect boggy approaches and choose a durable pitch carefully.

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.

Did this match your night?Share a quick observation to help improve this beta forecast.Give feedback

Daytime · exposed rockClimbing & scramblingBetaGusts near 60 mph increase the seriousness of exposed ground. 0/100Poor · Very poor View detailsHide details

Generic exposed-rock guidance

Full climbing & scrambling outlook

Conditions for exposed scrambling look very poor (0/100). Rain during the useful part of the day is likely to leave rock wet and more slippery. 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. Gusts may reach about 60 mph; crosswinds can make exposed ridges substantially more serious.

Rock surfaceWet rock likelyPeak gust58 mphRain0.6 mm

Main factorsgusts around 60 mphwet rock likely

Mapped rock across the summit and available routes Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks Foel Fras Volcanic Complex

Origin: Sedimentary and igneous
Rock family: Volcanic rock
Mapping: BGS Geology 50K · 1:50,000
Rock-response profile: Low confidence

View the summit BGS record

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.

Mapped variation

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.

Summit mapping Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks Foel Fras Volcanic Complex Around 1,048 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Basalt Foel Grach Basalt Formation 932–1,053 m samples Seen on Peak Carneddau Aber Falls

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Felsic tuff Capel Curig Volcanic Formation Around 680 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Mudstone and siltstone Cwm Eigiau Formation Around 767 m Seen on Peak Carneddau Ogwen

Often positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.

BGS record

Route sample Rhyolite Unnamed Igneous Intrusion, Ordovician Around 488 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Sandstone Llewelyn Volcanic Group Around 955 m Seen on Peak Carneddau Ogwen

Often 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 record

Route sample Siltstone Capel Curig Volcanic Formation Around 580 m Seen on Peak Carneddau Ogwen

Often positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.

BGS record

See sampled routes

Peak Carneddau Aber Falls932–1,053 m samplesBasalt

Peak Carneddau Ogwen488–1,048 m samplesFelsic tuff · Mudstone and siltstone · Rhyolite · Sandstone · Siltstone · Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks

Generic 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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Monday 7 September 2026Medium confidence

Overall hill weather42/100Poor

Wind39 mph SW Gusts54 mph Feels-1°C Rain0.0 mm Cloud-free summit60% Cloud base through day1,000–2,200 m Freezing levelAbove summit Daylight06:35–19:51 · 13.3 h

Forecast confidence: Rain could reach the main walking period or hold off until later; forecast models disagree on the timing.

Spate watch

Burns and unbridged crossings may rise quickly. Assess them at the water and turn back if unsure.

Cloud-free timing: Around 75% early, falling to around 35% later.

A wild day on Carnedd Llewelyn: summit wind broadly 25-45 mph, with gusts 50-60 mph during the evening (gale-force winds). The ground is likely to be wet after recent rain. There could be a spate risk based on forecast rainfall. Burns and unbridged crossings may rise quickly. Most likely from around 00:00 until around 03:00 the following day. Much calmer lower down - generally 10-20 mph in the valley, rising towards the tops. Cloud base around 1200–1500 m in the morning, then around 1900–2200 m around midday and 1000–1300 m by late afternoon. The top is likely to drift in and out of cloud, with the best chance of a view from early morning into the afternoon. Cloud height is close to summit level at times, so small local changes could put the top in or out of cloud. about 11 hours of sunshine is indicated, with variable cloud giving brighter and duller spells. Little or no rain expected. Cold on top: air temperature broadly 2 to 6°C, feeling around -2 to 2°C in the wind - wrap up. Confidence moderate (Summit wind could be roughly 30-50 mph, which changes how difficult exposed walking may feel) - walker-height summit wind could reasonably be 30-50 mph, with gusts 42-70 mph. Cloud base is the least certain part of this - it could sit a couple of hundred metres either way, especially where it is close to summit level.

At this mountain

Sunshine and sky

Brighter and duller spells. Expect alternating brighter and duller spells.

Modelled sunshine11 h85% of daylight

Early1.7 h sunshine

Midday3.4 h sunshine

Later3.9 h sunshine

These are direct modelled sunshine hours during daylight, not the probability of sunshine. Cloud cover and summit cloud are assessed separately in the forecast above. Local hill cloud can still make an individual summit brighter or duller than the surrounding model grid.

Morning · 07:00–13:00Good

71/100

Afternoon & evening · 13:00–22:00Poor

14/100

Separate hill-weather grades help compare an early start with later conditions; the main daytime forecast above still covers the core walking day.

Overnight · 6 p.m.–9 a.m.Wild campingBetaGusts near 55 mph make meaningful shelter important. 39/100Poor · 600 m View detailsHide details

Night beginning Monday 7 September 2026

Full overnight outlook

Open-hillside camping looks poor overall around 600 m (39/100). A lower pitch near 300 m looks more comfortable; conditions are less suitable by 900 m. Open-ground gusts may reach about 55 mph, making exposed pitches a poor choice. Peak gusts increase from about 40 mph at 300 m to 55 mph at 900 m. A wet night is likely, with roughly 11.7 mm and rain liable to affect both pitching and packing up. From around 600 m upward, pitches may spend part of the night in cloud, bringing persistent damp and poor visibility. The coldest temperature falls from about 8°C at 300 m to 5°C at 900 m.

Overnight rain12 mm Open ground · 600 m30 mph · gusts 48 mph Morning pack-upDampness possible Sleeping-bag warmthISO comfort rating about 4°C or lower

Elevation reference (open ground)

300 m49/100 · mixed

Wind / gust: 25 / 40 mph
Typical / low: 8.7° / 8.0°C · much of the night
In cloud: Unlikely
Condensation: Moderate

600 m39/100 · poor

Wind / gust: 30 / 48 mph
Typical / low: 8.5° / 7.2°C · much of the night
In cloud: 25% of night
Condensation: Moderate

900 m24/100 · poor

Wind / gust: 35 / 56 mph
Typical / low: 7.2° / 5.0°C · a brief spell
In cloud: 38% of night
Condensation: Moderate

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 increase the seriousness of exposed ground. 0/100Poor · Very poor View detailsHide details

Generic exposed-rock guidance

Full climbing & scrambling outlook

Conditions for exposed scrambling look very poor (0/100). Some rock may still be damp or drying; polished slabs and vegetated sections could be notably worse. 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. Gusts may reach about 55 mph; crosswinds can make exposed ridges substantially more serious.

Rock surfaceDamp or dryingPeak gust53 mphRainPossible · 78%

Main factorsgusts around 55 mphdamp or incompletely dried rock possible

Mapped rock across the summit and available routes Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks Foel Fras Volcanic Complex

Origin: Sedimentary and igneous
Rock family: Volcanic rock
Mapping: BGS Geology 50K · 1:50,000
Rock-response profile: Low confidence

View the summit BGS record

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.

Mapped variation

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.

Summit mapping Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks Foel Fras Volcanic Complex Around 1,048 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Basalt Foel Grach Basalt Formation 932–1,053 m samples Seen on Peak Carneddau Aber Falls

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Felsic tuff Capel Curig Volcanic Formation Around 680 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Mudstone and siltstone Cwm Eigiau Formation Around 767 m Seen on Peak Carneddau Ogwen

Often positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.

BGS record

Route sample Rhyolite Unnamed Igneous Intrusion, Ordovician Around 488 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Sandstone Llewelyn Volcanic Group Around 955 m Seen on Peak Carneddau Ogwen

Often 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 record

Route sample Siltstone Capel Curig Volcanic Formation Around 580 m Seen on Peak Carneddau Ogwen

Often positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.

BGS record

See sampled routes

Peak Carneddau Aber Falls932–1,053 m samplesBasalt

Peak Carneddau Ogwen488–1,048 m samplesFelsic tuff · Mudstone and siltstone · Rhyolite · Sandstone · Siltstone · Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks

Generic 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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Tuesday 8 September 2026Medium confidence

Overall hill weather42/100Poor

Wind32 mph W Gusts45 mph Feels-2°C Rain2.5 mm Cloud-free summit45% Cloud base through day1,500–1,800 m Freezing levelAbove summit Daylight06:36–19:49 · 13.2 h

Forecast confidence: Rain timing may shift by several hours, which could change how much of the main walking period stays dry.

Cloud-free timing: Around 60% early, falling to around 50% later.

A mixed day on Carnedd Llewelyn: summit wind broadly 25-35 mph, with gusts 40-50 mph early in the morning (gale-force winds). Much calmer lower down - generally 15-25 mph in the valley, rising towards the tops. Cloud base mostly around 1500–1800 m through daylight. The top is likely to drift in and out of cloud, with the best chance of a view during the morning. Cloud height is close to summit level at times, so small local changes could put the top in or out of cloud. Cloud is likely to hang lowest on western slopes; the eastern side should see somewhat higher bases and better breaks. about 2 hours of sunshine is indicated, with variable cloud giving brighter and duller spells. Some rain is likely, with around 2-5 mm indicated; timing and local totals remain uncertain. Cold on top: air temperature broadly 2 to 6°C, feeling around -4 to 0°C in the wind - wrap up. Confidence moderate (forecast models agree on the walking impact of the wind) - walker-height summit wind could reasonably be 27-37 mph, with gusts 38-52 mph. Cloud base is the least certain part of this - it could sit a couple of hundred metres either way, especially where it is close to summit level.

At this mountain

Sunshine and sky

Brighter and duller spells. Expect alternating brighter and duller spells.

Modelled sunshine1.9 h15% of daylight

Early0 h sunshine

Midday1.9 h sunshine

Later0 h sunshine

These are direct modelled sunshine hours during daylight, not the probability of sunshine. Cloud cover and summit cloud are assessed separately in the forecast above. Local hill cloud can still make an individual summit brighter or duller than the surrounding model grid.

Morning · 07:00–13:00Poor

49/100

Afternoon & evening · 13:00–22:00Poor

35/100

Separate hill-weather grades help compare an early start with later conditions; the main daytime forecast above still covers the core walking day.

Overnight · 6 p.m.–9 a.m.Wild campingBetaGusts near 45 mph make meaningful shelter important. 71/100Good · 600 m View detailsHide details

Night beginning Tuesday 8 September 2026

Full overnight outlook

Open-hillside camping looks reasonable overall around 600 m (71/100). A lower pitch near 300 m looks more comfortable; conditions are less suitable by 900 m. Open-ground gusts may reach about 45 mph, making exposed pitches a poor choice. Peak gusts increase from about 30 mph at 300 m to 45 mph at 900 m. Around 1.9 mm is forecast, with rain liable to affect both pitching and packing up. A wet pack-up remains possible from dew or brief dampness toward dawn. The coldest temperature falls from about 7.7°C at 300 m to 5.2°C at 900 m.

Overnight rain1.9 mm Open ground · 600 m25 mph · gusts 39 mph Morning pack-upDampness possible Sleeping-bag warmthISO comfort rating about 4°C or lower

Elevation reference (open ground)

300 m78/100 · promising

Wind / gust: 21 / 32 mph
Typical / low: 8.5° / 7.7°C · much of the night
In cloud: Unlikely
Condensation: Low

600 m71/100 · reasonable

Wind / gust: 25 / 39 mph
Typical / low: 8.0° / 7.3°C · much of the night
In cloud: Unlikely
Condensation: Low

900 m39/100 · poor

Wind / gust: 30 / 46 mph
Typical / low: 5.5° / 5.2°C · much of the night
In cloud: Unlikely
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.

Did this match your night?Share a quick observation to help improve this beta forecast.Give feedback

Daytime · exposed rockClimbing & scramblingBetaGusts near 45 mph increase the seriousness of exposed ground. 0/100Poor · Very poor View detailsHide details

Generic exposed-rock guidance

Full climbing & scrambling outlook

Conditions for exposed scrambling look very poor (0/100). Rain during the useful part of the day is likely to leave rock wet and more slippery. 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. Gusts may reach about 45 mph; crosswinds can make exposed ridges substantially more serious.

Rock surfaceWet rock likelyPeak gust44 mphRain2.3 mm

Main factorsgusts around 45 mphwet rock likely

Mapped rock across the summit and available routes Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks Foel Fras Volcanic Complex

Origin: Sedimentary and igneous
Rock family: Volcanic rock
Mapping: BGS Geology 50K · 1:50,000
Rock-response profile: Low confidence

View the summit BGS record

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.

Mapped variation

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.

Summit mapping Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks Foel Fras Volcanic Complex Around 1,048 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Basalt Foel Grach Basalt Formation 932–1,053 m samples Seen on Peak Carneddau Aber Falls

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Felsic tuff Capel Curig Volcanic Formation Around 680 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Mudstone and siltstone Cwm Eigiau Formation Around 767 m Seen on Peak Carneddau Ogwen

Often positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.

BGS record

Route sample Rhyolite Unnamed Igneous Intrusion, Ordovician Around 488 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Sandstone Llewelyn Volcanic Group Around 955 m Seen on Peak Carneddau Ogwen

Often 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 record

Route sample Siltstone Capel Curig Volcanic Formation Around 580 m Seen on Peak Carneddau Ogwen

Often positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.

BGS record

See sampled routes

Peak Carneddau Aber Falls932–1,053 m samplesBasalt

Peak Carneddau Ogwen488–1,048 m samplesFelsic tuff · Mudstone and siltstone · Rhyolite · Sandstone · Siltstone · Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks

Generic 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.

Did this match your experience?Tell us about the rock surface and wind to help improve this beta forecast.Give feedback

Wednesday 9 September 2026Medium confidence

Overall hill weather47/100Poor

Wind27 mph W Gusts37 mph Feels-2°C Rain0.7 mm Cloud-free summit30% Cloud base through day700–1,700 m Freezing levelAbove summit Daylight06:38–19:46 · 13.1 h

Forecast confidence: Forecast models differ on whether meaningful rain reaches the hills during the main walking period.

Cloud-free timing: Cloudier around midday at about 15%; around 40% early and 45% later.

A grey, cloudy day on Carnedd Llewelyn: summit wind broadly 15-30 mph, with gusts 30-40 mph early in the morning (strong winds). Much calmer lower down - generally 5-15 mph in the valley, rising towards the tops. Cloud base around 1200–1500 m in the morning, then around 700–1000 m around midday and 1400–1700 m by late afternoon. The top is likely to drift in and out of cloud, with the best chance of a view from late afternoon into the evening. Cloud is likely to hang lowest on western slopes; the eastern side should see somewhat higher bases and better breaks. A generally bright day is indicated, with about 12 hours of sunshine. Little or no rain expected. Cold on top: air temperature broadly 2 to 6°C, feeling around -4 to 0°C in the wind - wrap up. Confidence moderate (Summit wind could be roughly 20-35 mph, which changes how difficult exposed walking may feel) - walker-height summit wind could reasonably be 20-35 mph, with gusts 28-48 mph.

At this mountain

Sunshine and sky

Generally bright. A generally bright day is indicated.

Modelled sunshine12 h92% of daylight

Early2 h sunshine

Midday4 h sunshine

Later4 h sunshine

These are direct modelled sunshine hours during daylight, not the probability of sunshine. Cloud cover and summit cloud are assessed separately in the forecast above. Local hill cloud can still make an individual summit brighter or duller than the surrounding model grid.

Morning · 07:00–13:00Poor

41/100

Afternoon & evening · 13:00–22:00Mixed

53/100

Separate hill-weather grades help compare an early start with later conditions; the main daytime forecast above still covers the core walking day.

Overnight · 6 p.m.–9 a.m.Wild campingBetaAbout 1.4 mm is forecast, with rain liable to affect both pitching and packing up. 78/100Good · 600 m View detailsHide details

Night beginning Wednesday 9 September 2026

Full overnight outlook

Open-hillside camping looks promising overall around 600 m (78/100). A lower pitch near 300 m looks more comfortable; conditions are less suitable by 900 m. It may be breezy on open ground, with gusts near 25 mph. Peak gusts increase from about 20 mph at 300 m to 25 mph at 900 m. Around 1.4 mm is forecast, with rain liable to affect both pitching and packing up. From around 900 m upward, pitches may spend part of the night in cloud, with high condensation risk, persistent damp and poor visibility; ventilation will matter. The coldest temperature falls from about 7.4°C at 300 m to 5.6°C at 900 m.

Overnight rain1.4 mm Open ground · 600 m13 mph · gusts 22 mph Morning pack-upDampness possible Sleeping-bag warmthISO comfort rating about 4°C or lower

Elevation reference (open ground)

300 m80/100 · promising

Wind / gust: 11 / 18 mph
Typical / low: 9.0° / 7.4°C · much of the night
In cloud: Unlikely
Condensation: Moderate

600 m78/100 · promising

Wind / gust: 13 / 22 mph
Typical / low: 8.4° / 7.4°C · much of the night
In cloud: Unlikely
Condensation: Moderate

900 m64/100 · reasonable

Wind / gust: 15 / 26 mph
Typical / low: 6.3° / 5.6°C · much of the night
In cloud: 25% of night
Condensation: High

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.

Did this match your night?Share a quick observation to help improve this beta forecast.Give feedback

Daytime · exposed rockClimbing & scramblingBetaGusts near 35 mph increase the seriousness of exposed ground. 14/100Poor · Very poor View detailsHide details

Generic exposed-rock guidance

Full climbing & scrambling outlook

Conditions for exposed scrambling look very poor (14/100). Rain during the useful part of the day is likely to leave rock wet and more slippery. 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. Gusts may reach about 35 mph; crosswinds can make exposed ridges substantially more serious. Cloud may also make route-finding and retreat harder.

Rock surfaceWet rock likelyPeak gust35 mphRain0.6 mm

Main factorsgusts around 35 mphwet rock likelymuch of the route may be in cloud

Mapped rock across the summit and available routes Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks Foel Fras Volcanic Complex

Origin: Sedimentary and igneous
Rock family: Volcanic rock
Mapping: BGS Geology 50K · 1:50,000
Rock-response profile: Low confidence

View the summit BGS record

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.

Mapped variation

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.

Summit mapping Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks Foel Fras Volcanic Complex Around 1,048 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Basalt Foel Grach Basalt Formation 932–1,053 m samples Seen on Peak Carneddau Aber Falls

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Felsic tuff Capel Curig Volcanic Formation Around 680 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Mudstone and siltstone Cwm Eigiau Formation Around 767 m Seen on Peak Carneddau Ogwen

Often positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.

BGS record

Route sample Rhyolite Unnamed Igneous Intrusion, Ordovician Around 488 m Seen on Peak Carneddau Ogwen

Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

BGS record

Route sample Sandstone Llewelyn Volcanic Group Around 955 m Seen on Peak Carneddau Ogwen

Often 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 record

Route sample Siltstone Capel Curig Volcanic Formation Around 580 m Seen on Peak Carneddau Ogwen

Often positive when dry, but smooth, polished or slabby sections can become markedly more slippery when damp.

BGS record

See sampled routes

Peak Carneddau Aber Falls932–1,053 m samplesBasalt

Peak Carneddau Ogwen488–1,048 m samplesFelsic tuff · Mudstone and siltstone · Rhyolite · Sandstone · Siltstone · Volcaniclastic rocks (both pyroclastic and reworked volcanic rocks

Generic 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.

Did this match your experience?Tell us about the rock surface and wind to help improve this beta forecast.Give feedback

Carnedd Llewelyn weather forecast.

Today on Carnedd Llewelyn.

Seven-day Carnedd Llewelyn forecast.

Full overnight outlook

Elevation reference (open ground)

Full climbing & scrambling outlook

7 rock types appear across the available route samples

Full overnight outlook

Elevation reference (open ground)

Full climbing & scrambling outlook

7 rock types appear across the available route samples

Full overnight outlook

Elevation reference (open ground)

Full climbing & scrambling outlook

7 rock types appear across the available route samples

Full overnight outlook

Elevation reference (open ground)

Full climbing & scrambling outlook

7 rock types appear across the available route samples

Full overnight outlook

Elevation reference (open ground)

Full climbing & scrambling outlook

7 rock types appear across the available route samples

Full overnight outlook

Elevation reference (open ground)

Full climbing & scrambling outlook

7 rock types appear across the available route samples

Full overnight outlook

Elevation reference (open ground)

Full climbing & scrambling outlook

7 rock types appear across the available route samples

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