Mountain Weather

Arenig Fach weather forecast.

689 m summit in Eryri (Snowdonia). 8 forecast days covering wind, cloud, rain and temperature, updated 22 September 2026 at 16:08 UTC.

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Confidence: Medium
Overall hill weather65/100Mixed
Possible inversionLow confidence · Morning
Wind5-15 mph southerly Gusts10-20 mph Feels like10 to 14°C PrecipitationLittle or none Cloud-free summit estimate50% Cloud base through day600-900 m Freezing levelAbove summit DaylightSunrise 07:00 · Sunset 19:14 · 12.2 hours daylight

The day on the hill

Frequent summit cloud on Arenig Fach: summit wind broadly 5-15 mph, with gusts 10-20 mph at times (light winds).

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

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.

Cloud-free timing: Around 60% early, falling to around 45% later.

Sunshine context Model-grid estimate, not summit sunshine

The surrounding model grid indicates 3.5 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
0 h
Midday
2.8 h
Later
0 h

Overnight forecast: 17:00–08:00 (UK local time), in Wild camping below.

Morning · 08:00–12:00 Mixed Summit winds around 0-10 mph. Gusts around 5-15 mph are possible on exposed ground.
64/100
Afternoon · 12:00–17:00 Mixed Summit winds around 0-15 mph. Gusts around 10-20 mph are possible on exposed ground.
66/100

Compare an early start with later conditions. The main forecast above covers the day in more detail.

Overnight · 17:00–08:00Wild campingBetaGusts near 30 mph make meaningful shelter important. 59/100Mixed · 600 m View detailsHide details
Night beginning Tuesday 22 September 2026

Full overnight outlook

Open-hillside camping looks mixed overall around 600 m (59/100). Open-ground gusts may reach about 30 mph. Seek meaningful shelter. Peak gusts range from about 25 mph at 300 m to 30 mph at 600 m. Around 4.9 mm is forecast, including rain around pack-up. Condensation risk is high near 300 and 600 m, so a wet pack-up is possible. Ventilation will matter.

Overnight rain4.9 mm Open ground · 600 m14 mph · gusts 31 mph Morning pack-upDampness possible Sleeping-bag warmthISO comfort rating about 8°C or lower

Moon overnight

Waxing gibbous moon

Illuminated disc
86%
Moonrise
17:55 BST
Moonset
02:48 next morning BST

Extensive cloud may limit moonlight. Illumination describes the sunlit part of the Moon, not brightness at your pitch.

Overnight window: 22 Sep, 17:00 BST to 23 Sep, 08:00 BST. Approximate open-horizon times; hills can hide the Moon. Still take a headtorch.

Elevation reference (open ground)

300 m64/100 · reasonable
Wind / gust
12 mph / 26 mph
Typical / low
12.8°C / 11.9°C
In cloud
0% of modelled night
Condensation
High
600 m59/100 · mixed
Wind / gust
14 mph / 31 mph
Typical / low
12.8°C / 11.9°C
In cloud
0% 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 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.

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

Approximate height is enough, please do not share an exact wild-camp location.

Daytime · exposed rockClimbing & scramblingBetaCloud may complicate route-finding and retreat. Mixed68/100 View detailsHide details
Generic exposed-rock guidance

Full climbing & scrambling outlook

Conditions for exposed scrambling look fair (68/100). Rock is likely to be mostly dry, though seepage and shaded holds are not resolved. The mapped summit rock is Felsic tuff (Aran Fawddwy Formation). Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery. Cloud may also make route-finding and retreat harder.

Rock surfaceProbably dryPeak gust14 mphRain0.0 mm
Main concernmuch of the route may be in cloud
Mapped summit rock Felsic tuff Aran Fawddwy Formation
Origin
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 bedrock mapping; the actual route may cross different rock, superficial deposits, polish, lichen or seepage.

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

A broad surface report is enough; you do not need to identify a particular route.

Overnight · Aurora, stars & meteorsAfter darkBetaNight-sky guidance is unavailable for this night. View forecastClose forecast

After dark: aurora and stargazing

Night-sky guidance is unavailable for this night. This does not mean clear skies or no aurora.

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.

Does the weather shape your plans?Optional hill-user research. One answer helps; further questions are up to you.Take part

Help the Mountain Decisions Project understand how forecasts influence hill days, including when plans stay the same. Findings will be shared publicly as summaries, not individual responses.

This is about Arenig Fach on Tuesday 22 September 2026. It asks about intentions, not whether you actually went out. No name or account is needed.

Open the questions to take part.

About the research and your privacy · Already been out? Share that experience instead

Confidence: Medium
Overall hill weather23/100Poor
Wind15-45 mph northwesterly Gusts50-60 mph Feels like2 to 6°C PrecipitationAround 10-20 mm Cloud-free summit estimate75% Cloud base through day600-1,800 m Freezing levelAbove summit DaylightSunrise 07:01 · Sunset 19:12 · 12.2 hours daylight

The day on the hill

Strong gusts on Arenig Fach: summit wind broadly 15-45 mph, with gusts 50-60 mph at times (gale-force mean winds at times).

Things to watch

Severe spate risk from the morning into the afternoon, with forecast rain and subsequent runoff. Timings are approximate, not a guarantee of safe crossings afterwards. Burns and unbridged crossings may become difficult or impassable. Turn back if a crossing looks unsafe.

Wind & exposure

Much calmer lower down - generally 5-15 mph in the valley, rising towards the tops. Gusts may knock you off balance on exposed ground, even between spells of lighter wind.

Cloud & views

Cloud base around 600–900 m in the morning, lifting to 1000–1300 m around midday and 1500–1800 m by late afternoon. The top is likely to drift in and out of cloud, with the best chance of a view from around midday into the evening.

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. Sunny spells are possible away from summit cloud, but may not reach the top while it is in cloud.

Rain & temperature

Rain is likely to include a heavy spell, with around 10-20 mm expected over the assessed day. Forecast models differ on summit wind strength: around 34-43 mph at walker height, with gusts 48-60 mph.

Forecast confidence

Cloud height remains uncertain, especially where it is close to summit level. Exposed tops may feel chilly in the wind.

A windproof layer will help, with an extra warm layer for stops. If clothing gets wet, you can cool more quickly.

Keep a dry warm layer protected. Forecast models differ on whether meaningful rain reaches the hills during the main walking period.

Cloud-free timing: Around 40% early, improving to around 95% later.

Sunshine context Model-grid estimate, not summit sunshine

The surrounding model grid indicates 4.5 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
0 h
Midday
1.5 h
Later
2 h

Overnight forecast: 17:00–08:00 (UK local time), in Wild camping below.

Morning · 08:00–12:00 Poor Summit winds around 25-35 mph early in the morning, easing to 10-20 mph later. Gusts around 50-60 mph are possible on exposed ground. Gusts may knock you off balance on exposed ground, even between spells of lighter wind. Rain is forecast during this period. Some forecast models bring rain during the morning, while others keep it mostly dry.
17/100
Afternoon · 12:00–17:00 Poor Winds ease compared with the morning. Rain also eases. Summit winds around 10-20 mph. Gusts around 20-30 mph are possible on exposed ground. Summit cloud is more persistent early in this period, with better prospects later.
29/100

Compare an early start with later conditions. The main forecast above covers the day in more detail.

Overnight · 17:00–08:00Wild campingBetaA broadly very good night on a well-chosen pitch. 94/100Excellent · 600 m View detailsHide details
Night beginning Wednesday 23 September 2026

Full overnight outlook

Open-hillside camping looks very good overall around 600 m (94/100). It may be breezy on open ground, with gusts near 20 mph. Little overnight rain is forecast.

Overnight rain0.0 mm Open ground · 600 m10 mph · gusts 22 mph Morning pack-upNo wet signal Sleeping-bag warmthISO comfort rating about 6°C or lower

Moon overnight

Waxing gibbous moon

Illuminated disc
92%
Moonrise
18:09 BST
Moonset
04:07 next morning BST

Views of the Moon may come and go through cloud breaks. Illumination describes the sunlit part of the Moon, not brightness at your pitch.

Overnight window: 23 Sep, 17:00 BST to 24 Sep, 08:00 BST. Approximate open-horizon times; hills can hide the Moon. Still take a headtorch.

Elevation reference (open ground)

300 m96/100 · very good
Wind / gust
8 mph / 18 mph
Typical / low
8.7°C / 8.5°C · much of the night
In cloud
0% of modelled night
Condensation
Low
600 m94/100 · very good
Wind / gust
10 mph / 22 mph
Typical / low
8.7°C / 8.5°C · much of the night
In cloud
0% 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 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

Approximate height is enough, please do not share an exact wild-camp location.

Daytime · exposed rockClimbing & scramblingBetaWet rock is likely. Gusts near 55 mph may affect balance on exposed rock. Poor0/100 View detailsHide details
Generic exposed-rock guidance

Full climbing & scrambling outlook

Conditions for exposed scrambling look very poor (0/100). Rain during the climbing period is likely to leave rock wet and more slippery. The mapped summit rock is Felsic tuff (Aran Fawddwy Formation). Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery. Gusts may reach about 55 mph. Crosswinds can make exposed ridges substantially more serious.

Rock surfaceWet rock likelyPeak gust55 mphRain15.9 mm
Main factorsgusts around 55 mphwet rock likely
Mapped summit rock Felsic tuff Aran Fawddwy Formation
Origin
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 bedrock mapping; the actual route may cross different rock, superficial deposits, polish, lichen or seepage.

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

A broad surface report is enough; you do not need to identify a particular route.

Overnight · Aurora, stars & meteorsAfter darkBetaNight-sky guidance is unavailable for this night. View forecastClose forecast

After dark: aurora and stargazing

Night-sky guidance is unavailable for this night. This does not mean clear skies or no aurora.

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.

Does the weather shape your plans?Optional hill-user research. One answer helps; further questions are up to you.Take part

Help the Mountain Decisions Project understand how forecasts influence hill days, including when plans stay the same. Findings will be shared publicly as summaries, not individual responses.

This is about Arenig Fach on Wednesday 23 September 2026. It asks about intentions, not whether you actually went out. No name or account is needed.

Open the questions to take part.

About the research and your privacy · Already been out? Share that experience instead

Confidence: Medium
Overall hill weather66/100Mixed
Wind15-30 mph southwesterly Gusts30-40 mph Feels like4 to 8°C PrecipitationLittle or none Cloud-free summit estimate90% Cloud base through day1,000-1,700 m Freezing levelAbove summit DaylightSunrise 07:03 · Sunset 19:09 · 12.1 hours daylight

The day on the hill

On Arenig Fach: summit wind broadly 15-30 mph, with gusts 30-40 mph at times (strong winds).

Wind & exposure

Much calmer lower down - generally 5-15 mph in the valley, rising towards the tops. Cloud-height uncertainty could put the summit in or out of cloud.

Clear spells may be difficult to time.

Rain & temperature

The ground is likely to be wet after recent rain. Little or no rain is forecast.

Forecast models differ on summit wind strength: around 23-28 mph at walker height, with gusts 32-40 mph.

Forecast confidence

Cloud height remains uncertain, especially where it is close to summit level. Buffeting may affect balance on exposed ground, particularly near ridges and edges.

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 95% early, falling to around 65% later.

Sunshine context Model-grid estimate, not summit sunshine

The surrounding model grid indicates 8.4 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 h
Midday
3 h
Later
2.4 h

Overnight forecast: 17:00–08:00 (UK local time), in Wild camping below.

Morning · 08:00–12:00 Mixed Summit winds around 5-15 mph early in the morning, strengthening to 15-25 mph later. Gusts around 25-35 mph are possible on exposed ground.
68/100
Afternoon · 12:00–17:00 Mixed Summit winds around 15-25 mph. Gusts around 30-40 mph are possible on exposed ground.
63/100

Compare an early start with later conditions. The main forecast above covers the day in more detail.

Overnight · 17:00–08:00Wild campingBetaGusts near 35 mph make meaningful shelter important. 54/100Mixed · 600 m View detailsHide details
Night beginning Thursday 24 September 2026

Full overnight outlook

Open-hillside camping looks mixed overall around 600 m (54/100). Open-ground gusts may reach about 35 mph. Seek meaningful shelter. Peak gusts range from about 25 mph at 300 m to 35 mph at 600 m. Wind direction may change substantially during the night. Shelter that works at dusk may be less effective later. Roughly 6.7 mm is forecast overnight, including rain around pack-up. Pitches near 600 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 and 600 m. Ventilation will matter.

Overnight rain6.7 mm Open ground · 600 m18 mph · gusts 33 mph Morning pack-upDampness possible Sleeping-bag warmthISO comfort rating about 6°C or lower

Moon overnight

Waxing gibbous moon

Illuminated disc
97%
Moonrise
18:20 BST
Moonset
05:26 next morning BST

Cloud at the reference camping height may hide the Moon. Illumination describes the sunlit part of the Moon, not brightness at your pitch.

Overnight window: 24 Sep, 17:00 BST to 25 Sep, 08:00 BST. Approximate open-horizon times; hills can hide the Moon. Still take a headtorch.

Elevation reference (open ground)

300 m59/100 · mixed
Wind / gust
15 mph / 27 mph
Typical / low
12.2°C / 9.4°C · a brief spell
In cloud
0% of modelled night
Condensation
High
600 m54/100 · mixed
Wind / gust
18 mph / 33 mph
Typical / low
12.1°C / 9.3°C · a brief spell
In cloud
80% of modelled 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

Approximate height is enough, please do not share an exact wild-camp location.

Daytime · exposed rockClimbing & scramblingBetaRock may be damp or still drying. Gusts near 35 mph may affect balance on exposed rock. Mixed56/100 View detailsHide details
Generic exposed-rock guidance

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 Felsic tuff (Aran Fawddwy Formation). Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery. Gusts may reach about 35 mph. Crosswinds can make exposed ridges substantially more serious.

Rock surfaceDry overhead; seepage uncertainPeak gust37 mphRain0.0 mm
Main factorsgusts around 35 mphdamp or incompletely dried rock possible
Mapped summit rock Felsic tuff Aran Fawddwy Formation
Origin
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 bedrock mapping; the actual route may cross different rock, superficial deposits, polish, lichen or seepage.

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

A broad surface report is enough; you do not need to identify a particular route.

Overnight · Aurora, stars & meteorsAfter darkBetaNight-sky guidance is unavailable for this night. View forecastClose forecast

After dark: aurora and stargazing

Night-sky guidance is unavailable for this night. This does not mean clear skies or no aurora.

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.

Does the weather shape your plans?Optional hill-user research. One answer helps; further questions are up to you.Take part

Help the Mountain Decisions Project understand how forecasts influence hill days, including when plans stay the same. Findings will be shared publicly as summaries, not individual responses.

This is about Arenig Fach on Thursday 24 September 2026. It asks about intentions, not whether you actually went out. No name or account is needed.

Open the questions to take part.

About the research and your privacy · Already been out? Share that experience instead

Confidence: Medium
Overall hill weather67/100Mixed
Wind5-20 mph westerly Gusts15-25 mph Feels like2 to 6°C PrecipitationAround 2-5 mm Cloud-free summit estimate55% Cloud base through day500-1,100 m Freezing levelAbove summit DaylightSunrise 07:05 · Sunset 19:07 · 12.0 hours daylight

The day on the hill

On Arenig Fach: summit wind broadly 5-20 mph, with gusts 15-25 mph at times (a moderate breeze).

Cloud & views

Cloud base around 500–800 m through the morning, lifting to 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 late afternoon into the evening.

Cloud-height uncertainty could put the summit in or out of cloud. Clear spells may be difficult to time.

Very little direct sunshine is likely, with extensive cloud. Drizzle is forecast for much of the day.

The forecast total is around 2-5 mm, but local amounts will vary.

Forecast confidence

Cloud height remains uncertain, especially where it is close to summit level. Exposed tops may feel chilly in the wind.

A windproof layer will help, with an extra warm layer for stops. If clothing gets wet, you can cool more quickly.

Keep a dry warm layer protected. Rain could reach the main walking period or hold off until later. Forecast models disagree on the timing.

Cloud-free timing: Around 35% early, improving to around 65% later.

Sunshine context Model-grid estimate, not summit sunshine

The surrounding model grid indicates 0 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
0 h
Midday
0 h
Later
0 h

Overnight forecast: 17:00–08:00 (UK local time), in Wild camping below.

Morning · 08:00–12:00 Mixed Summit winds around 5-15 mph. Gusts around 10-20 mph are possible on exposed ground. Rain is forecast during this period. Some forecast models bring rain during the morning, while others keep it mostly dry.
56/100
Afternoon · 12:00–17:00 Good Rain eases compared with the morning. Summit winds around 5-15 mph. Gusts around 10-20 mph are possible on exposed ground. Summit cloud is more persistent early in this period, with better prospects later. Rain is forecast during this period. Rain is possible during the afternoon, but forecast models disagree on whether it will fall.
78/100

Compare an early start with later conditions. The main forecast above covers the day in more detail.

Overnight · 17:00–08:00Wild campingBetaGusts near 30 mph make meaningful shelter important. 54/100Mixed · 600 m View detailsHide details
Night beginning Friday 25 September 2026

Full overnight outlook

Open-hillside camping looks mixed overall around 600 m (54/100). A lower pitch near 300 m looks more comfortable. Conditions are less suitable by 600 m. Open-ground gusts may reach about 30 mph. Seek meaningful shelter. Peak gusts range from about 25 mph at 300 m to 30 mph at 600 m. Little overnight rain is forecast. Pitches near 600 m may spend part of the night in cloud, bringing damp conditions and poor visibility while cloud is present. Condensation risk is high near 600 m. Ventilation will matter.

Overnight rain0.2 mm Open ground · 600 m17 mph · gusts 30 mph Morning pack-upDampness possible Sleeping-bag warmthISO comfort rating about 6°C or lower

Moon overnight

Near-full moon

Illuminated disc
99%
Moonrise
18:30 BST
Moonset
06:47 next morning BST

Cloud at the reference camping height may hide the Moon. Illumination describes the sunlit part of the Moon, not brightness at your pitch.

Overnight window: 25 Sep, 17:00 BST to 26 Sep, 08:00 BST. Approximate open-horizon times; hills can hide the Moon. Still take a headtorch.

Elevation reference (open ground)

300 m83/100 · promising
Wind / gust
14 mph / 25 mph
Typical / low
9.7°C / 8.6°C · much of the night
In cloud
0% of modelled night
Condensation
Moderate
600 m54/100 · mixed
Wind / gust
17 mph / 30 mph
Typical / low
9.6°C / 8.5°C · much of the night
In cloud
87% of modelled 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

Approximate height is enough, please do not share an exact wild-camp location.

Daytime · exposed rockClimbing & scramblingBetaWet rock is likely. Poor31/100 View detailsHide details
Generic exposed-rock guidance

Full climbing & scrambling outlook

Conditions for exposed scrambling look poor (31/100). Rain during the climbing period is likely to leave rock wet and more slippery. The mapped summit rock is Felsic tuff (Aran Fawddwy Formation). Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery. Cloud may also make route-finding and retreat harder.

Rock surfaceWet rock likelyPeak gust18 mphRain4.7 mm
Main factorswet rock likelymuch of the route may be in cloud
Mapped summit rock Felsic tuff Aran Fawddwy Formation
Origin
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 bedrock mapping; the actual route may cross different rock, superficial deposits, polish, lichen or seepage.

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

A broad surface report is enough; you do not need to identify a particular route.

Overnight · Aurora, stars & meteorsAfter darkBetaNight-sky guidance is unavailable for this night. View forecastClose forecast

After dark: aurora and stargazing

Night-sky guidance is unavailable for this night. This does not mean clear skies or no aurora.

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.

Does the weather shape your plans?Optional hill-user research. One answer helps; further questions are up to you.Take part

Help the Mountain Decisions Project understand how forecasts influence hill days, including when plans stay the same. Findings will be shared publicly as summaries, not individual responses.

This is about Arenig Fach on Friday 25 September 2026. It asks about intentions, not whether you actually went out. No name or account is needed.

Open the questions to take part.

About the research and your privacy · Already been out? Share that experience instead

Confidence: Medium
Overall hill weather39/100Poor
Wind20-35 mph southwesterly Gusts35-45 mph Feels like4 to 8°C PrecipitationAround 2-5 mm Cloud-free summit estimate45% Cloud base through day500-1,100 m Freezing levelAbove summit DaylightSunrise 07:06 · Sunset 19:04 · 12.0 hours daylight

The day on the hill

A wet day with extensive summit cloud on Arenig Fach: summit wind broadly 20-35 mph, with gusts 35-45 mph at times (strong winds).

Wind & exposure

Much calmer lower down - generally 10-20 mph in the valley, rising towards the tops.

Cloud & views

Cloud base around 500–800 m in the morning, then around 800–1100 m around midday and 500–800 m by late afternoon. The top is likely to drift in and out of cloud, with the best chance of a view from midday into the afternoon.

Cloud-height uncertainty could put the summit in or out of cloud. Clear spells may be difficult to time.

Cloud may hang lower on southwestern slopes and lift somewhat on the northeastern side, but local terrain can differ. Sunny spells are possible away from summit cloud, but may not reach the top while it is in cloud.

Drizzle is forecast for much of the day, with some passing showers too. The forecast total is around 2-5 mm, but local amounts will vary.

Forecast models differ on summit wind strength: around 17-43 mph at walker height, with gusts 24-60 mph.

Rain & temperature

The ground is likely to be wet after recent rain.

Forecast confidence

Cloud height remains uncertain, especially where it is close to summit level. Buffeting may affect balance on exposed ground, particularly near ridges and edges.

Forecast models disagree on cloud cover.

Cloud-free timing: Best around midday at about 50%, compared with around 35% early and 35% later.

Sunshine context Model-grid estimate, not summit sunshine

The surrounding model grid indicates 9.6 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
Less than 1 hour
Midday
4 h
Later
3 h

Overnight forecast: 17:00–08:00 (UK local time), in Wild camping below.

Morning · 08:00–12:00 Poor Summit winds around 20-30 mph. Gusts around 30-40 mph are possible on exposed ground. Buffeting may affect balance on exposed ground, particularly near ridges and edges. Rain is forecast during this period.
33/100
Afternoon · 12:00–17:00 Poor Summit winds around 15-35 mph. Gusts around 35-45 mph are possible on exposed ground. Buffeting may affect balance on exposed ground, particularly near ridges and edges. Rain is forecast during this period.
45/100

Compare an early start with later conditions. The main forecast above covers the day in more detail.

Overnight · 17:00–08:00Wild campingBetaExposed camping is not recommended near 600 m: gusts may reach about 40 mph. Sustained winds may reach about 30 mph at times. Choose an alternative off the exposed hill. Do not rely on finding shelter after setting out. 19/100Poor · 600 m View detailsHide details
Night beginning Saturday 26 September 2026

Full overnight outlook

Exposed camping is not recommended near 600 m: gusts may reach about 40 mph. Sustained winds may reach about 30 mph at times. Choose an alternative off the exposed hill. Do not rely on finding shelter after setting out. Open-hillside camping looks very poor overall around 600 m (19/100). Peak gusts range from about 35 mph at 300 m to 40 mph at 600 m. Around 2.2 mm is forecast, including rain around pitching time. Pitches near 600 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 and 600 m. Ventilation will matter.

Overnight rain2.2 mm Open ground · 600 m28 mph · gusts 42 mph Morning pack-upDampness possible Sleeping-bag warmthISO comfort rating about 6°C or lower

Moon overnight

Near-full moon

Illuminated disc
100%
Moonrise
18:41 BST
Moonset
Outside this window

Cloud at the reference camping height may hide the Moon. Illumination describes the sunlit part of the Moon, not brightness at your pitch.

Overnight window: 26 Sep, 17:00 BST to 27 Sep, 08:00 BST. Approximate open-horizon times; hills can hide the Moon. Still take a headtorch.

Elevation reference (open ground)

300 m39/100 · poor
Wind / gust
24 mph / 35 mph
Typical / low
10.8°C / 10.2°C
In cloud
0% of modelled night
Condensation
High
600 m19/100 · very poor
Wind / gust
28 mph / 42 mph
Typical / low
10.6°C / 9.8°C · a brief spell
In cloud
100% of modelled 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

Approximate height is enough, please do not share an exact wild-camp location.

Daytime · exposed rockClimbing & scramblingBetaWet rock is likely. Gusts near 40 mph may affect balance on exposed rock. Poor3/100 View detailsHide details
Generic exposed-rock guidance

Full climbing & scrambling outlook

Conditions for exposed scrambling look very poor (3/100). Rain during the climbing period is likely to leave rock wet and more slippery. The mapped summit rock is Felsic tuff (Aran Fawddwy Formation). Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery. 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 mphRain2.5 mm
Main factorsgusts around 40 mphwet rock likelymuch of the route may be in cloud
Mapped summit rock Felsic tuff Aran Fawddwy Formation
Origin
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 bedrock mapping; the actual route may cross different rock, superficial deposits, polish, lichen or seepage.

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

A broad surface report is enough; you do not need to identify a particular route.

Overnight · Aurora, stars & meteorsAfter darkBetaNight-sky guidance is unavailable for this night. View forecastClose forecast

After dark: aurora and stargazing

Night-sky guidance is unavailable for this night. This does not mean clear skies or no aurora.

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.

Does the weather shape your plans?Optional hill-user research. One answer helps; further questions are up to you.Take part

Help the Mountain Decisions Project understand how forecasts influence hill days, including when plans stay the same. Findings will be shared publicly as summaries, not individual responses.

This is about Arenig Fach on Saturday 26 September 2026. It asks about intentions, not whether you actually went out. No name or account is needed.

Open the questions to take part.

About the research and your privacy · Already been out? Share that experience instead

Confidence: Medium
Overall hill weather0/100Severe hill conditions
Wind25-40 mph southwesterly Gusts45-55 mph Feels like2 to 6°C PrecipitationAround 5-10 mm Cloud-free summit estimate30% Cloud base through day500-800 m Freezing levelAbove summit DaylightSunrise 07:08 · Sunset 19:02 · 11.9 hours daylight

The day on the hill

Strong gusts and frequent summit cloud on Arenig Fach: summit wind broadly 25-40 mph, with gusts 45-55 mph at times (strong winds).

Things to watch

Thunderstorms are possible from the morning into the evening. Avoid committing to exposed ridges if storms begin to build.

If a thunderstorm develops, sudden gusts and heavy rain can change conditions quickly.

Wind & exposure

Much calmer lower down - generally 10-20 mph in the valley, rising towards the tops. Gusts may knock you off balance on exposed ground, even between spells of lighter wind.

Cloud & views

Cloud base mostly around 500–800 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.

Cloud may hang lower on southwestern slopes and lift somewhat on the northeastern side, but local terrain can differ. Any sunshine may be confined to lower ground or breaks away from the summit.

Drizzle is forecast for much of the day. The forecast total is around 5-10 mm, but local amounts will vary.

Forecast models differ on summit wind strength: around 25-42 mph at walker height, with gusts 35-58 mph.

Forecast confidence

Cloud height remains uncertain, especially where it is close to summit level. Exposed tops may feel chilly in the wind.

A windproof layer will help, with an extra warm layer for stops. If clothing gets wet, you can cool more quickly.

Keep a dry warm layer protected. Thunderstorm timing is inherently uncertain and may shift by several hours.

0 is the bottom of the scale. Use the hazard details to judge how severe conditions could be.

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.

Morning · 08:00–12:00 Severe hill conditions Summit winds around 30-40 mph. Gusts around 45-55 mph are possible on exposed ground. Gusts may knock you off balance on exposed ground, even between spells of lighter wind. Rain is forecast during this period. Some forecast models bring rain during the morning, while others keep it mostly dry.
0/100
Afternoon · 12:00–17:00 Severe hill conditions More rain is expected. Summit winds around 30-40 mph in the early afternoon, easing to 25-35 mph later. Gusts around 45-55 mph are possible on exposed ground. Gusts may knock you off balance on exposed ground, even between spells of lighter wind. Rain is forecast during this period. Rain is possible during the afternoon, but forecast models disagree on whether it will fall.
0/100

Compare an early start with later conditions. The main forecast above covers the day in more detail.

Overnight · 17:00–08:00Wild campingBetaCondensation risk is high near 600 m. 54/100Mixed · 600 m View detailsHide details
Night beginning Sunday 27 September 2026

Full overnight outlook

Open-hillside camping looks mixed overall around 600 m (54/100). A lower pitch near 300 m looks more comfortable. Conditions are less suitable by 600 m. It may be breezy on open ground, with gusts near 30 mph. Peak gusts range from about 25 mph at 300 m to 30 mph at 600 m. A little rain may coincide with pitching or packing up. Pitches near 600 m may spend part of the night in cloud, bringing damp conditions and poor visibility while cloud is present. Condensation risk is high near 600 m. Ventilation will matter.

Overnight rain0.4 mm Open ground · 600 m11 mph · gusts 28 mph Morning pack-upDampness possible Sleeping-bag warmthISO comfort rating about 6°C or lower

Moon overnight

Waning gibbous moon

Illuminated disc
98%
Moonrise
18:52 BST
Moonset
Outside this window

Cloud at the reference camping height may hide the Moon. Illumination describes the sunlit part of the Moon, not brightness at your pitch.

Overnight window: 27 Sep, 17:00 BST to 28 Sep, 08:00 BST. Approximate open-horizon times; hills can hide the Moon. Still take a headtorch.

Elevation reference (open ground)

300 m82/100 · promising
Wind / gust
9 mph / 23 mph
Typical / low
10.0°C / 9.4°C · several hours
In cloud
0% of modelled night
Condensation
Moderate
600 m54/100 · mixed
Wind / gust
11 mph / 28 mph
Typical / low
9.5°C / 9.1°C · much of the night
In cloud
93% of modelled 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

Approximate height is enough, please do not share an exact wild-camp location.

Daytime · exposed rockClimbing & scramblingBetaModerate thunderstorm risk. Avoid exposed rock if storms develop. Wet rock is likely. Gusts near 50 mph may affect balance on exposed rock. Poor0/100 View detailsHide details
Generic exposed-rock guidance

Full climbing & scrambling outlook

Conditions for exposed scrambling look very poor (0/100). Rain during the climbing period is likely to leave rock wet and more slippery. The mapped summit rock is Felsic tuff (Aran Fawddwy Formation). Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery. Gusts may reach about 50 mph. Crosswinds can make exposed ridges substantially more serious. Cloud may also make route-finding and retreat harder. Moderate thunderstorm risk, broadly from the morning into the evening. Avoid committing to exposed ground if storms develop.

Rock surfaceWet rock likelyPeak gust50 mphRain8.1 mm
Main factorsmoderate thunderstorm risk on exposed groundgusts around 50 mphwet rock likely
Mapped summit rock Felsic tuff Aran Fawddwy Formation
Origin
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 bedrock mapping; the actual route may cross different rock, superficial deposits, polish, lichen or seepage.

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

A broad surface report is enough; you do not need to identify a particular route.

Overnight · Aurora, stars & meteorsAfter darkBetaNight-sky guidance is unavailable for this night. View forecastClose forecast

After dark: aurora and stargazing

Night-sky guidance is unavailable for this night. This does not mean clear skies or no aurora.

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.

Does the weather shape your plans?Optional hill-user research. One answer helps; further questions are up to you.Take part

Help the Mountain Decisions Project understand how forecasts influence hill days, including when plans stay the same. Findings will be shared publicly as summaries, not individual responses.

This is about Arenig Fach on Sunday 27 September 2026. It asks about intentions, not whether you actually went out. No name or account is needed.

Open the questions to take part.

About the research and your privacy · Already been out? Share that experience instead

Confidence: Unavailable
Overall hill weather93/100Excellent
Wind5-15 mph southerly Gusts5-15 mph Feels like6 to 10°C PrecipitationLittle or none Cloud-free summit estimate80% Freezing levelAbove summit DaylightSunrise 07:10 · Sunset 19:00 · 11.8 hours daylight

The day on the hill

Little rain and limited summit cloud on Arenig Fach: summit wind broadly 5-15 mph, with gusts 5-15 mph at times (light winds).

Cloud & views

Cloud base around 900–1200 m in the morning, then around 1300–1600 m around midday and 700–1000 m by late afternoon. 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.

Rain & temperature

Little or no rain is forecast. Forecast models disagree markedly on summit wind strength.

Check again nearer the time.

Forecast confidence

Overall confidence is unavailable: insufficient comparable wind, rain guidance.

Cloud-free timing: Around 80% early, falling to around 60% later.

Sunshine context Model-grid estimate, not summit sunshine

The surrounding model grid indicates 10.9 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.

Early
2 h
Midday
4 h
Later
2.9 h

Overnight forecast: 17:00–08:00 (UK local time), in Wild camping below.

Morning · 08:00–12:00 Excellent Summit winds around 0-10 mph. Gusts around 5-15 mph are possible on exposed ground.
92/100
Afternoon · 12:00–17:00 Excellent Summit winds around 5-15 mph. Gusts around 5-15 mph are possible on exposed ground.
94/100

Compare an early start with later conditions. The main forecast above covers the day in more detail.

Overnight · 17:00–08:00Wild campingBetaExposed camping is not recommended near 300 and 600 m: gusts may reach about 55 mph. Sustained winds may reach about 40 mph at times. Choose an alternative off the exposed hill. Do not rely on finding shelter after setting out. 9/100Poor · 600 m View detailsHide details
Night beginning Monday 28 September 2026

Full overnight outlook

Exposed camping is not recommended near 300 and 600 m: gusts may reach about 55 mph. Sustained winds may reach about 40 mph at times. Choose an alternative off the exposed hill. Do not rely on finding shelter after setting out. Open-hillside camping looks very poor overall around 600 m (9/100). Peak gusts range from about 50 mph at 300 m to 55 mph at 600 m. Around 2.3 mm is forecast, including rain around pack-up. Pitches near 600 m may spend part of the night in cloud, bringing damp conditions and poor visibility while cloud is present.

Overnight rain2.3 mm Open ground · 600 m21 mph · gusts 57 mph Morning pack-upDampness possible Sleeping-bag warmthISO comfort rating about 6°C or lower

Moon overnight

Waning gibbous moon

Illuminated disc
94%
Moonrise
19:06 BST
Moonset
Outside this window

Cloud at the reference camping height may hide the Moon. Illumination describes the sunlit part of the Moon, not brightness at your pitch.

Overnight window: 28 Sep, 17:00 BST to 29 Sep, 08:00 BST. Approximate open-horizon times; hills can hide the Moon. Still take a headtorch.

Elevation reference (open ground)

300 m19/100 · very poor
Wind / gust
18 mph / 48 mph
Typical / low
10.5°C / 9.1°C · several hours
In cloud
0% of modelled night
Condensation
Moderate
600 m9/100 · very poor
Wind / gust
21 mph / 57 mph
Typical / low
10.2°C / 9.1°C · several hours
In cloud
47% of modelled 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.

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

Approximate height is enough, please do not share an exact wild-camp location.

Daytime · exposed rockClimbing & scramblingBetaRock may be damp or still drying. Good82/100 View detailsHide details
Generic exposed-rock guidance

Full climbing & scrambling outlook

Conditions for exposed scrambling look good (82/100). Recent rain may leave seepage and damp rock, especially on shaded sections. The mapped summit rock is Felsic tuff (Aran Fawddwy Formation). Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery.

Rock surfaceDry overhead; seepage uncertainPeak gust12 mphRain0.0 mm
Main concerndamp or incompletely dried rock possible
Mapped summit rock Felsic tuff Aran Fawddwy Formation
Origin
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 bedrock mapping; the actual route may cross different rock, superficial deposits, polish, lichen or seepage.

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

A broad surface report is enough; you do not need to identify a particular route.

Overnight · Aurora, stars & meteorsAfter darkBetaNight-sky guidance is unavailable for this night. View forecastClose forecast

After dark: aurora and stargazing

Night-sky guidance is unavailable for this night. This does not mean clear skies or no aurora.

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.

Does the weather shape your plans?Optional hill-user research. One answer helps; further questions are up to you.Take part

Help the Mountain Decisions Project understand how forecasts influence hill days, including when plans stay the same. Findings will be shared publicly as summaries, not individual responses.

This is about Arenig Fach on Monday 28 September 2026. It asks about intentions, not whether you actually went out. No name or account is needed.

Open the questions to take part.

About the research and your privacy · Already been out? Share that experience instead

Confidence: Unavailable
Overall hill weather2/100Poor
Wind35-50 mph southwesterly Gusts55-65 mph Feels like2 to 6°C PrecipitationAround 10-20 mm Cloud-free summit estimate70% Cloud base through day600-1,600 m Freezing levelAbove summit DaylightSunrise 07:12 · Sunset 18:57 · 11.8 hours daylight

The day on the hill

Strong gusts and frequent summit cloud on Arenig Fach: summit wind broadly 35-50 mph, with gusts 55-65 mph at times (gale-force mean winds at times). Heavier showers may bring brief, stronger gusts and rapidly reduced visibility.

Things to watch

Possible spate risk from the morning into the afternoon, with forecast rain and subsequent runoff. Timings are approximate, not a guarantee of safe crossings afterwards. Burns and unbridged crossings may rise quickly. Turn back if a crossing looks unsafe.

Wind & exposure

Much calmer lower down - generally 10-20 mph in the valley, rising towards the tops.

Cloud & views

Cloud base around 600–900 m through the morning, lifting to 1300–1600 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-height uncertainty could put the summit in or out of cloud. Clear spells may be difficult to time.

Sunny spells are possible away from summit cloud, but may not reach the top while it is in cloud.

Rain & temperature

Rain and drizzle are forecast for much of the day, with some passing showers too. The forecast total is around 10-20 mm, but local amounts will vary.

Forecast models disagree markedly on summit wind strength. Check again nearer the time.

Exposed tops may feel chilly in the wind. A windproof layer will help, with an extra warm layer for stops.

If clothing gets wet, you can cool more quickly. Keep a dry warm layer protected.

The strongest gusts could knock you over on exposed ground. Avoid exposed ridges and edges.

Forecast confidence

Overall confidence is unavailable: insufficient comparable wind, rain guidance.

Cloud-free timing: Around 55% early, improving to around 95% later.

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.

Early
0 h
Midday
2.1 h
Later
2.9 h

Overnight forecast: 17:00–08:00 (UK local time), in Wild camping below.

Morning · 08:00–12:00 Severe hill conditions Summit winds around 35-45 mph. Gusts around 55-65 mph are possible on exposed ground. The strongest gusts could knock you over on exposed ground. Avoid exposed ridges and edges. Rain is forecast during this period.
0/100
Afternoon · 12:00–17:00 Poor Summit winds around 30-40 mph. Gusts around 50-60 mph are possible on exposed ground. Gusts may knock you off balance on exposed ground, even between spells of lighter wind. Summit cloud is more persistent early in this period, with better prospects later. Rain is forecast during this period.
15/100

Compare an early start with later conditions. The main forecast above covers the day in more detail.

Overnight · 17:00–08:00Wild campingBetaExposed camping is not recommended near 300 and 600 m: gusts may reach about 65 mph. Sustained winds may reach about 45 mph at times. Choose an alternative off the exposed hill. Do not rely on finding shelter after setting out. 0/100Poor · 600 m View detailsHide details
Night beginning Tuesday 29 September 2026

Full overnight outlook

Exposed camping is not recommended near 300 and 600 m: gusts may reach about 65 mph. Sustained winds may reach about 45 mph at times. Choose an alternative off the exposed hill. Do not rely on finding shelter after setting out. Open-hillside camping looks very poor overall around 600 m (0/100). Peak gusts range from about 55 mph at 300 m to 65 mph at 600 m. Roughly 12 mm is forecast overnight, with rain liable to affect both pitching and packing up. Condensation risk is high near 300 and 600 m, so a wet pack-up is possible. Ventilation will matter.

Overnight rain12.0 mm Open ground · 600 m42 mph · gusts 65 mph Morning pack-upDampness possible Sleeping-bag warmthISO comfort rating about 6°C or lower

Moon overnight

Waning gibbous moon

Illuminated disc
87%
Moonrise
19:25 BST
Moonset
Outside this window

Extensive cloud may limit moonlight. Illumination describes the sunlit part of the Moon, not brightness at your pitch.

Overnight window: 29 Sep, 17:00 BST to 30 Sep, 08:00 BST. Approximate open-horizon times; hills can hide the Moon. Still take a headtorch.

Elevation reference (open ground)

300 m9/100 · very poor
Wind / gust
35 mph / 54 mph
Typical / low
10.2°C / 9.7°C · several hours
In cloud
0% of modelled night
Condensation
High
600 m0/100 · very poor
Wind / gust
42 mph / 65 mph
Typical / low
10.2°C / 9.7°C · several hours
In cloud
0% of modelled 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

Approximate height is enough, please do not share an exact wild-camp location.

Daytime · exposed rockClimbing & scramblingBetaWet rock is likely. Gusts near 60 mph may affect balance on exposed rock. Poor0/100 View detailsHide details
Generic exposed-rock guidance

Full climbing & scrambling outlook

Conditions for exposed scrambling look very poor (0/100). Rain during the climbing period is likely to leave rock wet and more slippery. The mapped summit rock is Felsic tuff (Aran Fawddwy Formation). Often grippy when dry, but volcanic rocks vary widely; wet lichen, smooth holds and local seepage can still make them slippery. Gusts may reach about 60 mph. Crosswinds can make exposed ridges substantially more serious. Cloud may also make route-finding and retreat harder.

Rock surfaceWet rock likelyPeak gust61 mphRain12.1 mm
Main factorsgusts around 60 mphwet rock likelymuch of the route may be in cloud
Mapped summit rock Felsic tuff Aran Fawddwy Formation
Origin
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 bedrock mapping; the actual route may cross different rock, superficial deposits, polish, lichen or seepage.

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

A broad surface report is enough; you do not need to identify a particular route.

Overnight · Aurora, stars & meteorsAfter darkBetaNight-sky guidance is unavailable for this night. View forecastClose forecast

After dark: aurora and stargazing

Night-sky guidance is unavailable for this night. This does not mean clear skies or no aurora.

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.

Does the weather shape your plans?Optional hill-user research. One answer helps; further questions are up to you.Take part

Help the Mountain Decisions Project understand how forecasts influence hill days, including when plans stay the same. Findings will be shared publicly as summaries, not individual responses.

This is about Arenig Fach on Tuesday 29 September 2026. It asks about intentions, not whether you actually went out. No name or account is needed.

Open the questions to take part.

About the research and your privacy · Already been out? Share that experience instead

Weather data: Open-Meteo (CC BY 4.0). Adapted by Mountain Weather.

Forecast run: 2026-09-22

Keep exploring

Weather around Arenig Fach.

Compare the summit forecast with the wider regional picture and nearby peaks before choosing a route.

Regional mountain forecastEryri (Snowdonia)View area →
Arenig Fawr854 m · 4.7 km awayForecast →Carnedd y Filiast669 m · 5.9 km awayForecast →Moel Llyfnant751 m · 6.5 km awayForecast →Gallt y Daren619 m · 8.3 km awayForecast →

A forecast is part of the decision.

Mountain weather can differ sharply from conditions in the valley. Check official warnings, carry appropriate navigation and clothing, and be ready to change the plan. Read how Mountain Weather forecasts are produced and where their limits lie.

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