Condition Analysis
AI-powered assessment using site data and 14-day weather history
The Cromlech Boulders are currently wet and conditions are unsuitable for climbing. A prolonged spell of heavy rain over the past two weeks (125.8mm in 28 days), rain today with more heavy rain forecast through the week, and near-saturated humidity levels mean the rhyolite surfaces will be slippery and dangerous.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit roadside in the Llanberis Pass where funnelled SW winds can accelerate drying, but current humidity above 90% negates this advantage.
- Jerry's Roof and other overhanging problems may appear dry underneath but surrounding landing zones and top-outs will be saturated and slippery.
- Seepage from the hillside above (below Dinas Cromlech) can keep certain problems damp long after rain stops, particularly on the uphill faces of the boulders.
- The SW/W aspect normally aids drying, but persistent cloud cover and near-100% humidity today and this week eliminate any solar drying benefit.
Warnings
2
- Rhyolite becomes extremely slippery when wet — friction-dependent problems (slabs, mantels) are especially dangerous in current conditions.
- Landing zones around the boulders will be waterlogged and muddy, increasing the risk of ankle injuries from poor landings on crash pads.
Reasoning
The rock is currently wet — 5.4mm falling today on top of 22.3mm just five days ago, with only brief dry interludes that were insufficient to fully dry the boulders given humidity consistently above 85%.
Despite the exposed position and SW aspect, drying has been negligible this week because humidity has remained in the 85–95% range with persistent cloud cover, meaning evaporation rates are extremely low.
Rhyolite is non-porous so there is no structural damage risk from climbing when wet, but the friction loss on wet volcanic rock makes falls highly likely, especially on slabs and friction-dependent problems.
Early June should offer improving conditions, but this has been an exceptionally wet spell; daylight hours are long which would normally aid drying, but persistent frontal systems from the SW are keeping the pass saturated.
Contributing Factors
5
Over 125mm in the last 28 days with 31.8mm in the last 7 days alone, and rain falling again today (5.4mm), keeping all surfaces thoroughly wet.
Humidity has averaged 85% over the past week and is at 95–100% today, preventing any meaningful evaporation from rock surfaces.
There have been no consecutive fully dry days recently, so the boulders have had no sustained drying window.
Winds of 26+ km/h would normally aid drying on this exposed site, but with humidity near saturation the wind is carrying moisture rather than removing it.
88mm of rain is forecast over the next 6 days, with 21–28mm days on June 18–20, ensuring conditions will remain poor well into next week.
Recommendations
3
- Do not visit today or this week — conditions are wet and the forecast shows no meaningful drying window until at least June 22.
- If you are in the area, consider indoor climbing walls in Llanberis or Caernarfon as alternatives during this prolonged wet spell.
- Monitor conditions closely from June 22 onwards when the forecast shows a potential dry day; even then, assess the rock carefully on arrival before committing to climb.
Previous Analyses
Marginal — Assess Conditions
55%
2 days ago
After heavy rain on June 11 (22.3mm) followed by three mostly dry days with good wind, the rhyolite surfaces at the Cromlech Boulders are likely dry today during the afternoon window, but high background humidity and only a trace of rain this morning mean conditions should be visually confirmed on arrival. A prolonged wet spell begins tomorrow and persists through at least June 20.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The Cromlech Boulders sit roadside in Llanberis Pass which can funnel and accelerate wind from the SW/W, aiding surface drying but also channelling moisture-laden air during frontal weather.
- Jerry's Roof and other overhanging problems can retain seepage and drips from above even when vertical faces appear dry — check holds carefully on roof problems.
- The SW/W aspect means the boulders receive afternoon sun when it breaks through, which is the best window today given clearing around 10:00–17:00.
- The pass is notorious for lingering low cloud and mist that can keep surfaces damp even without measurable rain — today's 100% cloud cover limits solar drying.
Warnings
2
- A major wet spell (70+ mm) is forecast from June 16–20; do not plan climbing sessions at this venue during that period.
- Evening humidity rises sharply after 18:00 today (82–98%), so surfaces may become greasy — pack up before dusk.
Reasoning
The last significant rain was 22.3mm on June 11, followed by two fully dry days (June 12–14) with strong westerly/northerly winds (28–36 km/h), so surface moisture from that event should have cleared, though a 0.1mm trace at 08:00 today and persistent high humidity may leave a light film.
Strong winds (22–36 km/h) from the W/N over the past three days on an exposed SW/W-facing site would dry non-porous rhyolite surfaces efficiently, and afternoon temperatures reaching 20°C today further aid evaporation of any residual dampness.
Rhyolite is non-porous and does not suffer structural weakening when wet; the only risk is reduced friction on damp surfaces.
Early June in Snowdonia frequently brings prolonged Atlantic frontal systems; the current wet pattern with ~120mm over 28 days is typical, but the incoming 5-day forecast of 72mm of rain will keep the venue wet for the rest of the week.
Contributing Factors
6
June 12–14 were essentially dry (only 0.1mm on June 12) with strong winds, giving ample time for non-porous rhyolite to shed surface moisture from the June 11 deluge.
A 0.1mm trace at 08:00 today may leave light dampness on holds, though this should evaporate by mid-morning in the wind.
Humidity averaging 84% over the past week and 75% today limits evaporative drying and may leave a residual moisture film on rock surfaces.
The exposed position in Llanberis Pass with winds of 20–24 km/h today accelerates surface drying on the non-porous rhyolite.
15.8mm forecast for June 16 marks the start of a prolonged wet spell totalling over 70mm across five days, closing the climbing window after today.
Hourly data shows dry conditions from 09:00 onwards with humidity dropping to 61–65% and temperatures near 20°C through the afternoon, offering a viable climbing window.
Recommendations
3
- If visiting today, aim for the afternoon window (11:00–17:00) when humidity is lowest and any morning trace moisture will have evaporated — touch-test holds before committing to harder problems.
- Avoid the Cromlech Boulders from Tuesday through at least Friday as heavy, sustained rainfall will keep surfaces wet and slippery.
- Bring a towel to dry holds if needed, and prioritise lower-grade problems to test friction before attempting anything committing.
Marginal — Assess Conditions
62%
3 days ago
After a very wet spell (over 50mm in the last week alone), the Cromlech Boulders have had two dry days with moderate wind, and the SW/W aspect should have aided drying. Surface conditions are likely improving but residual dampness in sheltered spots and seepage from the saturated ground above cannot be ruled out — a visual check on arrival is essential.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit directly below the steep hillside of Dinas Cromlech, so prolonged wet spells can cause seepage and runoff to affect the tops and backs of boulders even after rain has stopped.
- Jerry's Roof and the overhanging problems can retain drip-fed moisture on holds for longer than vertical faces due to water tracking along the underside of the roof.
- The roadside position in the Llanberis Pass means the boulders are exposed to the prevailing SW wind, which significantly aids surface drying on the SW/W-facing aspects.
- After sustained wet periods the grassy landings can become sodden, affecting pad placement and increasing the risk of slipping on approach and descent.
Warnings
2
- Rain is forecast to return from June 16, with heavy falls June 17–19 — conditions will deteriorate significantly and climbing will likely be unsafe from midweek.
- Wet rhyolite is extremely slippery; if any hold feels damp, do not attempt the problem.
Reasoning
Two consecutive dry days following 22.3mm on June 11 and a prolonged wet fortnight; surface moisture on exposed faces is likely gone, but sheltered and north-facing facets or seepage-prone areas may still hold dampness.
The SW/W aspect receives good afternoon sun, and moderate-to-strong winds (19–36 km/h) over the last two days have aided evaporation, but the sheer volume of recent rain (51.6mm in 7 days) means deeper seepage lines may still be active.
Rhyolite is non-porous and does not suffer structural weakening when wet, so hold breakage is not a concern.
Early June in Snowdonia brings long daylight hours and reasonable solar angle, but the recent spell of cool, humid weather (average 11.8°C, 85% humidity) has limited drying efficiency.
Contributing Factors
6
Over 50mm fell in the last 7 days across multiple events, saturating the ground and keeping boulders intermittently wet for nearly two weeks.
No precipitation since June 12 (0.1mm trace), giving roughly 48 hours of drying with moderate wind.
The favourable aspect and exposed position with 19–36 km/h winds accelerate surface drying on the main climbing faces.
Average humidity of 85% over the past week slows evaporation and may leave a film of moisture on cooler, shaded surfaces.
Saturated ground above the boulders can feed seepage lines that persist well beyond the end of rain, particularly on the rear and tops of boulders.
Rain returns from June 16 with heavy falls forecast on June 17–19, limiting the drying window to tomorrow at best.
Recommendations
3
- Tomorrow (June 15) offers the best window — arrive after midday to maximise solar drying and visually inspect holds for moisture before committing to any problem.
- Avoid north-facing or sheltered facets of boulders and any problems fed by seepage from the hillside above; focus on the open, sun-exposed SW/W faces.
- Bring a towel to dry holds if isolated dampness is found, and check landing zones — pads may sink into saturated grass.
Do Not Climb
45%
4 days ago
Despite today being nominally dry, the Cromlech Boulders have been subjected to an extremely wet period — over 60mm in the past week alone with rain on almost every day — and only one consecutive dry day so far. With humidity at 83% and temperatures well below seasonal norms, surface moisture is likely still present in sheltered areas, and a prolonged wet spell is forecast from June 16th onward.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit roadside at the base of Dinas Cromlech and can collect runoff and seepage from the hillside above after prolonged rain, meaning they stay damp longer than their exposed position might suggest.
- The SW/W aspect helps with afternoon sun but the Llanberis Pass acts as a wind funnel, and in the current cool, humid conditions this can keep surfaces clammy rather than drying them effectively.
- Jerry's Roof and other overhanging problems may stay drier underneath but surrounding landings and slab problems will be the last to dry.
- The extremely popular nature of this venue means climbing on marginal conditions risks polishing the rhyolite — even though structural damage isn't a concern, friction degradation from wet traffic is real.
Warnings
2
- Damp rhyolite can be extremely slippery with little visual indication of moisture — test friction thoroughly before committing to any moves above your comfort level.
- A major wet spell (60mm+) is forecast from June 16–18; do not plan climbing for that period.
Reasoning
After 60.6mm of rain in the past 7 days with only one dry day, and humidity averaging 87%, surface moisture is very likely still present on many boulder faces despite the non-porous nature of the rock.
One dry day with moderate westerly winds (26.6 km/h) and the SW/W aspect will have helped evaporate standing water, but cooler-than-average temperatures (13.7°C max) and high humidity (83%) significantly slow complete surface drying, particularly in sheltered nooks and north-facing facets.
Rhyolite is non-porous and not at risk of structural weakening, but climbing on damp surfaces risks polishing the crystalline texture that gives this rock its legendary friction.
Early June in Snowdonia should offer reasonable drying conditions, but this period has been unusually wet and cool, with temperatures 3–5°C below seasonal norms, limiting the expected summer drying advantage.
Contributing Factors
7
Over 60mm fell in the past 7 days across 6 of 7 days, saturating the ground and keeping surfaces persistently damp.
A single dry day is insufficient to fully dry boulder surfaces after such a prolonged wet spell, especially with high ambient humidity.
Humidity averaging 87% over the past week and 83% today inhibits evaporation and can cause condensation on cool rock surfaces.
The exposed position with 26.6 km/h westerly winds today aids surface drying on wind-facing aspects.
The south-westerly aspect receives afternoon sun which will help dry exposed faces, though cloud cover may limit this benefit.
Rhyolite does not absorb water so only surface moisture needs to evaporate, enabling faster drying than porous alternatives.
Over 70mm is forecast from June 16–18, meaning any drying window is very narrow before conditions deteriorate again.
Recommendations
3
- Wait for a second full dry day with lower humidity before committing — if tomorrow (June 14th) stays dry as forecast, June 15th could offer a viable window but check conditions on arrival.
- If you do visit, test friction carefully on lower-grade slabs before attempting anything committing — damp rhyolite can feel deceptively grippy until it isn't.
- Plan to climb before June 16th if possible, as heavy rain is forecast from midweek onward and conditions will reset to poor.
Do Not Climb
35%
5 days ago
The Cromlech Boulders have been subjected to an extremely wet period with 66mm in the last 7 days and 22mm just yesterday, and today has seen further light precipitation with very high humidity (86%). Although rhyolite is non-porous and dries relatively quickly, the persistent saturation of the environment — including moss, lichen, and ground seepage — means surfaces are very likely still damp and slippery.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit below the steep hillside of Dinas Cromlech, and after prolonged heavy rain, surface runoff and seepage from above can keep certain faces wet long after the rain stops.
- The SW/W aspect is favourable for afternoon drying, but the Llanberis Pass funnels cloud and mist which can maintain surface dampness even during nominally dry spells.
- Jerry's Roof and other overhanging problems may stay drier underneath but surrounding landings and slab problems will be affected by the saturated ground conditions.
- At 250m in the Pass, orographic cloud and hill fog are common during unsettled spells and can deposit moisture even when no rain is officially recorded.
Warnings
2
- Rock surfaces are very likely slippery after 10+ days of near-continuous rain — falling on damp rhyolite is a serious injury risk, especially on highball problems.
- Ground conditions around the boulders will be waterlogged; expect muddy and slippery landings which reduce crashpad effectiveness.
Reasoning
With 22mm yesterday, 5mm the day before, and only 0.2mm today combined with 86% humidity, rock surfaces are almost certainly still carrying residual moisture from the prolonged wet spell.
Strong westerly winds (35 km/h today) and the exposed SW/W aspect will aid surface evaporation, but with persistent high humidity (86–95% over recent days) and no meaningful dry window yet established, effective drying has been minimal.
Rhyolite is non-porous so there is no structural risk from moisture; the concern is purely friction loss on wet or damp surfaces.
Early June should offer reasonable drying potential, but this has been an unusually wet and cool spell for the season with temperatures well below average, limiting evaporative drying.
Contributing Factors
6
66mm in the last 7 days including 22mm yesterday means the boulders and surrounding environment are thoroughly saturated.
Zero consecutive dry days to date — today still recorded 0.2mm and there has been no sustained break from precipitation since early June.
Humidity has averaged 88% over the past week, severely limiting evaporative drying even during rain-free hours.
The exposed position and 35 km/h westerly winds today will help strip surface moisture once rain ceases.
The south-west and west-facing aspect receives afternoon sun which aids drying when skies clear.
Rhyolite does not absorb water, so once surface moisture evaporates the rock can offer good friction relatively quickly.
Recommendations
3
- Wait for at least one full dry day with lower humidity before visiting — tomorrow (June 13) looks promising but conditions should be assessed on arrival.
- If you do visit, test friction carefully on lower, less consequential problems before committing to anything technical or high.
- Avoid slab and friction-dependent problems until surfaces have had extended sun and wind exposure; overhanging problems may be climbable sooner.
Do Not Climb
95%
6 days ago
The Cromlech Boulders are currently soaked from heavy, persistent rain — 26mm today alone on top of over 70mm in the past week. With 96–100% humidity and continuous rainfall through the afternoon, the rock will be wet and dangerously slippery all day and into tomorrow.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit roadside in the Llanberis Pass and catch direct weather from the prevailing SW/W systems, meaning they've been fully exposed to the prolonged wet spell.
- Despite the SW/W aspect normally aiding drying via solar gain, 100% cloud cover and near-saturation humidity have completely negated any drying potential for over a week.
- Seepage and pooling on horizontal features like Jerry's Roof and other overhanging lip problems can persist well after surface rock appears dry, requiring extra vigilance.
- At 250m altitude in the pass, orographic enhancement means rainfall totals here are likely higher than lowland stations suggest, compounding the moisture load.
Warnings
2
- Active heavy rain and 100% humidity make the rhyolite dangerously slippery — serious fall risk on all problems.
- The prolonged wet spell means ground around the boulders will be boggy and landing zones may be waterlogged, increasing injury risk from falls.
Reasoning
The rock is thoroughly wet: 26mm of rain today, 71.6mm in the past 7 days, and humidity has been 86–97% all week with no meaningful dry window.
Despite rhyolite's non-porous nature and the exposed aspect, zero drying has occurred — continuous rainfall, 100% cloud cover, and near-saturation humidity have kept surfaces perpetually wet.
Rhyolite is non-porous and does not suffer structural weakening when wet, so hold breakage risk is negligible.
Early June should offer reasonable drying conditions, but this unusually prolonged wet spell has produced autumn-like conditions with persistently saturated air and frequent frontal rain.
Contributing Factors
5
26.1mm of rain forecast today with the heaviest falls mid-morning to early afternoon, leaving rock thoroughly soaked.
Over 70mm in the past 7 days with no consecutive dry days means the surrounding environment is saturated and contributing to ambient moisture.
Humidity has been 86–97% for the past week and is forecast at 96–100% today, preventing any evaporative drying.
Winds of 25–34 km/h from the SW would normally aid drying, but with active rain and saturated air they provide no benefit today.
Rhyolite does not absorb water so will dry relatively quickly once rain stops and humidity drops — but those conditions are not present today.
Recommendations
3
- Do not climb today — the rock is actively wet and extremely slippery.
- Monitor conditions from Saturday 14 June onwards when a dry window with lower humidity and warmer temperatures is forecast.
- If visiting later this week, test friction carefully on easy ground first, as residual dampness in sheltered recesses can persist even when exposed surfaces feel dry.
Do Not Climb
92%
8 days ago
The Cromlech Boulders are currently saturated after a prolonged wet spell delivering nearly 70mm over the past week, with rain earlier today and more forecast through the afternoon and evening. Even though rhyolite dries relatively quickly, the persistent high humidity (86–97%) and ongoing showers mean surfaces will remain wet and dangerously slippery.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit roadside in the Llanberis Pass which can funnel moisture-laden SW/W winds, and drainage from the hillside above (below Dinas Cromlech) can cause prolonged seepage on some boulder faces even after rain stops.
- The SW/W aspect normally aids drying, but with 100% cloud cover for most of today and sustained high humidity above 80%, solar drying is negligible.
- Jerry's Roof and other overhung problems may appear dry underneath but surrounding landings and approach holds will be wet and greasy, creating a false sense of security.
- Roadside accessibility means it's tempting to 'just check' conditions, but the boulders' polished holds on popular problems like Jerry's Roof become exceptionally slippery with even trace moisture.
Warnings
2
- Rhyolite becomes extremely slippery when wet — do not attempt problems even if some faces appear surface-dry, as residual moisture and high humidity will severely reduce friction.
- Landings around the boulders will be waterlogged and soft after sustained heavy rain; pad placement may be compromised.
Reasoning
With 69.5mm in the past 7 days, rain earlier today, and humidity consistently above 85%, the rock surfaces are currently wet and will remain so throughout the day.
Despite the exposed position and moderate westerly winds (~29 km/h), the near-continuous cloud cover, high humidity, and intermittent showers today prevent any meaningful drying from occurring.
Rhyolite is non-porous and not at risk of structural damage from moisture, so the concern is purely friction loss and climber safety on slippery surfaces.
Early June should offer improving conditions, but this prolonged Atlantic weather pattern with repeated frontal systems is keeping the Pass thoroughly wet — unusual but not unheard of for early summer in Snowdonia.
Contributing Factors
5
Nearly 70mm of rain in the past 7 days with no consecutive dry days means the boulders and surrounding ground are thoroughly soaked.
Today has already seen rain with further showers forecast at 16:00 and through the evening, and humidity remains 67–96% all day.
Sustained westerly winds of 25–29 km/h would normally aid surface drying, but this benefit is overwhelmed by ongoing precipitation and saturated air.
The favourable south-west aspect is rendered ineffective today by near-total cloud cover (66–100%) preventing solar warming of the rock.
The next three days bring a further 33mm of rain with humidity at 87–95%, offering no drying window until at least June 13th.
Recommendations
3
- Do not climb today — the boulders are wet and conditions are unsafe due to friction loss on the rhyolite.
- The earliest realistic window for dry conditions is June 14th; plan to visit then if the dry forecast holds.
- If visiting mid-week, consider nearby indoor walls (such as Beacon Climbing Centre in Caernarfon) as an alternative until the weather breaks.
Do Not Climb
90%
9 days ago
The Cromlech Boulders are currently soaked after 24mm of rain today on top of 66mm in the past week, with humidity averaging 90%. Although rhyolite won't suffer structural damage, the rock will be extremely slippery and dangerous for bouldering — a discipline where friction is everything and falls onto pads from greasy holds carry real injury risk.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit roadside in the Llanberis Pass which can funnel moisture-laden SW winds, and today's heavy rain combined with near-saturated humidity means surface water will persist on overhangs and undercuts well into the afternoon.
- Jerry's Roof and other steep problems rely heavily on skin friction on rhyolite — even a thin moisture film dramatically reduces grip on these holds, making highball or committing moves genuinely dangerous.
- The Pass frequently experiences low cloud and mist at 250m which can keep surfaces damp even between rain showers, especially with humidity above 80%.
- The SW/W aspect is favourable for afternoon drying in summer, but with 100% cloud cover forecast for most of today and further rain expected this evening, meaningful drying is unlikely.
Warnings
2
- Rhyolite becomes extremely slippery when wet — bouldering falls from even moderate height onto pads can cause serious injury if holds are greasy.
- The forecast shows no reliable dry period in the next four days; do not assume a brief gap between showers means the rock is climbable.
Reasoning
The rock is currently saturated from 24mm of heavy overnight/early-morning rain, following a week that delivered over 66mm total, with ambient humidity at 90%+ through the morning hours.
Despite the exposed position and moderate SW winds (~20–27 km/h), near-complete cloud cover and high humidity (dropping only briefly to ~57% mid-afternoon) will severely limit evaporation, and further light rain is forecast from 18:00 onwards.
Rhyolite is non-porous so there is no structural damage risk; the concern is purely surface friction loss making holds dangerously slippery for bouldering.
Early June should offer reasonable drying conditions, but this is an unusually wet and cool spell with temperatures 5–10°C below seasonal norms, hampering the drying that would normally occur at this time of year.
Contributing Factors
7
24.4mm of rain fell predominantly overnight and early morning, leaving the boulders thoroughly wet with standing water likely in cracks and on ledges.
66mm in the past 7 days with zero consecutive dry days means the surrounding ground is saturated, contributing to ambient moisture and potential seepage.
Humidity has averaged 90% over the past week and remains above 80% for most of today, severely slowing surface evaporation.
A dry spell from roughly 07:00–18:00 with humidity dropping to ~57% at 13:00 and decent wind could begin surface drying on exposed faces.
Consistent 20+ km/h SW/W winds through the Pass aid surface evaporation on exposed boulder faces.
Max temperature of only 12.4°C is well below seasonal norms, reducing evaporative drying potential.
Light rain returns this evening and the next five days show continued unsettled weather with 26mm forecast, preventing any sustained drying period.
Recommendations
3
- Do not climb today — the rock will be wet and dangerously slippery even during the afternoon dry window, and bouldering on greasy rhyolite carries high injury risk.
- Monitor conditions closely from June 13–14 onwards when the forecast shows the first potential break in the rain; the exposed aspect and wind should allow relatively quick drying once rain stops.
- If visiting the Pass today regardless, consider walking or route-scouting rather than climbing, and check UKC or local social media for real-time condition reports before committing.
Do Not Climb
95%
10 days ago
The Cromlech Boulders are currently soaked after 73mm of rain in the last 7 days, with 16mm falling today and heavy rain forecast to continue through the coming week. The rock will be wet and dangerously slippery, with no meaningful drying window in sight.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit roadside in the Llanberis Pass which can funnel moisture-laden SW winds directly onto the rock, and the pass is notorious for low cloud and persistent drizzle even when surrounding areas are drier.
- Jerry's Roof and other overhanging problems may appear dry underneath but surrounding landings will be saturated and slippery, making spotting and pad placement hazardous.
- The SW/W aspect normally aids drying, but with prevailing SW rain-bearing winds this week the boulders are directly exposed to incoming precipitation rather than benefiting from shelter.
- At 250m altitude with temperatures around 12–13°C and near-saturated humidity, evaporative drying will be extremely slow even on this non-porous rhyolite.
Warnings
2
- Rhyolite becomes extremely slippery when wet — the renowned friction of the Cromlech Boulders is entirely absent in these conditions, creating serious fall risk.
- Landings around the boulders will be waterlogged and muddy, compromising pad placement and increasing the risk of ankle and knee injuries on descent.
Reasoning
The rock is thoroughly wet after 73mm in 7 days including 16mm today, with humidity at 95% preventing any meaningful surface drying.
Despite the exposed position and strong winds (~33 km/h SW), ongoing rain and near-saturated air mean no effective drying is occurring and none is expected for several days.
Rhyolite is non-porous so there is no structural damage risk, but the surface will be extremely slippery with severely reduced friction.
Early June should offer good conditions, but this is an unusually prolonged wet spell with temperatures well below seasonal norms, resulting in poor drying conditions.
Contributing Factors
5
73mm in the last 7 days with 16mm today means the rock surfaces are thoroughly saturated with standing water.
Average humidity of 92% over the past week with 95% today prevents any evaporative drying between showers.
Over 100mm of rain is forecast in the next 5 days, including a potential 52mm deluge on June 11th, ruling out any drying window.
Winds of 30+ km/h would normally aid drying, but they are carrying rain-laden air from the SW directly onto the boulders.
Temperatures around 12–13°C are well below late-spring norms, further slowing any potential evaporation.
Recommendations
3
- Do not visit the Cromlech Boulders this week — conditions are clearly unsuitable and the forecast shows no improvement until at least June 13th.
- Monitor conditions after June 13th, which currently shows no rain; even then, allow at least a full day of dry windy weather before attempting problems.
- If in the Llanberis Pass area, consider indoor climbing at Beacon or The Indy Wall as alternatives during this extended wet spell.
Do Not Climb
92%
11 days ago
The Cromlech Boulders are currently wet and unsuitable for climbing. Over 60mm of rain has fallen in the last seven days including 9.4mm today, humidity is at 91%, and the forecast shows persistent rain continuing through at least June 11th with no meaningful dry window.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit roadside in the Llanberis Pass which can channel mist and drizzle even when surrounding areas appear dry, keeping surfaces damp longer than weather stations suggest.
- Jerry's Roof and the steeper overhanging problems may appear surface-dry sooner than slabby or vertical faces, but seepage from above can keep holds greasy — always touch-test before committing.
- The SW/W aspect normally aids drying, but the prevailing SW rain-bearing winds mean the boulders receive the full brunt of Atlantic weather systems like the current one.
- Roadside puddles and ground saturation at 250m elevation mean even brief dry spells won't fully clear ambient moisture from the rock in current conditions.
Warnings
2
- Wet rhyolite is extremely slippery — friction-dependent slab and vertical problems become dangerous even with a thin film of moisture.
- The forecast shows no dry day until at least June 12th; do not assume brief dry spells between showers mean the rock is climbable.
Reasoning
The rock is currently wet, with 9.4mm of rain today on top of 61.7mm in the past week, and humidity at 91% — surfaces will be saturated.
Despite the exposed position and moderate winds (~30 km/h), continuous rainfall and near-saturated humidity (91–95%) prevent any meaningful drying between showers.
Rhyolite is non-porous and not at risk of structural damage when wet, so hold breakage is not a concern.
Early June should offer good conditions, but this prolonged Atlantic weather pattern with cool temperatures (12–15°C) and persistent rain is atypical and prevents the rapid drying normally expected at this time of year.
Contributing Factors
6
Over 60mm in the last 7 days with 9.4mm today means all boulder surfaces are currently wet.
Humidity averaging 91% over the past week prevents evaporation and keeps surfaces damp even between rain events.
12–16mm per day forecast through June 8th, with further rain on June 9–11, offers no dry window for recovery.
Strong winds (25–35 km/h) at the exposed roadside location would accelerate surface drying if rain stopped, but cannot overcome ongoing precipitation.
The volcanic rock does not absorb water so will dry quickly once conditions allow, but it is dangerously slippery while wet.
Temperatures of 10–15°C are well below seasonal averages, reducing evaporation rates.
Recommendations
3
- Do not visit for climbing until the current wet spell breaks — the earliest realistic dry window appears to be June 12th or later.
- Monitor local forecasts closely; rhyolite at this exposed site can dry within a few hours of sustained wind and sunshine, so conditions can change rapidly once rain stops.
- If you do visit the Pass in this weather, use the time to scout problems, check conditions, and enjoy the café rather than climbing on slippery rock.
Climbing Outlook