Condition Analysis
AI-powered assessment using site data and 14-day weather history
The boulders have had roughly 18 hours of dry weather following 7.2mm of rain on April 12, with moderate wind aiding surface drying. While rhyolite dries relatively quickly and the surface may be dry on exposed faces, the persistently high humidity (80%) and lack of strong sun mean sheltered or north-facing surfaces could still be damp — a visual check on arrival is essential before committing to climb.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The RAC Boulders sit in the Mymbyr valley which can funnel moisture and low cloud from the west, keeping humidity elevated even on nominally dry days.
- West-facing aspect means the boulders only receive afternoon/evening sun — morning sessions will rely entirely on wind for drying, and any shaded or east-facing facets will dry much more slowly.
- Roadside boulders at this altitude (200m) in the Nant Gwryd area are prone to condensation overnight and early morning, especially after the kind of saturated spell seen in recent weeks.
- Flat grassy landings can remain waterlogged after prolonged wet periods, potentially affecting pad placement and indicating residual ground moisture around the boulders.
Warnings
2
- Friction on rhyolite drops dramatically when damp — if holds feel glassy or slick, do not attempt problems, especially slab or friction-dependent lines.
- Heavy rain is forecast from tomorrow (April 14) onwards; today's afternoon window may be the only viable session this week.
Reasoning
The rock received 7.2mm of rain yesterday (April 12, mostly before 07:00) followed by ~18 hours of dry conditions with moderate westerly wind, but ambient humidity has remained around 76–90%, limiting evaporative drying.
Partial wind exposure and the westerly breeze (19–32 km/h) will have aided surface drying on exposed faces, but the west-facing aspect means no direct morning sun, and the high background humidity slows evaporation significantly.
Rhyolite is non-porous and not at risk of structural damage from moisture — the concern here is purely surface friction and climber safety.
Early April in Snowdonia brings unpredictable weather with frequent frontal systems; the recent pattern shows repeated heavy rain events with only brief dry windows, and the ground and surroundings are thoroughly saturated from nearly 200mm in the past 28 days.
Contributing Factors
8
7.2mm fell on April 12 (mostly early morning), giving only about 18 hours of drying time before today's session.
Nearly 200mm of rain in the past 28 days means the ground, moss, and cracks around the boulders are thoroughly saturated, contributing to ambient dampness.
Humidity has remained at 76–90% throughout the drying window, significantly slowing surface evaporation on the rock.
Sustained SW/W winds at 19–32 km/h through the drying period assist surface moisture removal on exposed faces.
Rhyolite does not absorb water, so surface moisture is the only concern and can evaporate relatively quickly once conditions allow.
No direct sunlight hits these boulders until the afternoon, so the morning drying period relies entirely on wind and ambient temperature.
No precipitation recorded since approximately 06:00 yesterday, giving a growing dry window through today.
13.1mm forecast for April 14 means today's window is brief and conditions will deteriorate again imminently.
Recommendations
3
- Visit in the afternoon when the west-facing boulders receive direct sun and have had maximum drying time — carefully touch-test holds before climbing.
- Focus on exposed, wind-facing problems rather than sheltered or overhung faces where moisture may linger in cracks and on slopers.
- Bring dry towels and pads with good coverage, as grassy landings may be waterlogged from the prolonged wet spell.
Previous Analyses
Do Not Climb
90%
2 days ago
The RAC Boulders are currently wet and unsuitable for climbing. Heavy rain yesterday (33.3mm) followed by further rain today (5.6mm) means the rock surfaces will be wet and dangerously slippery, with no drying window in the last 48 hours.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit roadside near Llynnau Mymbyr in a lakeside setting where ambient moisture from the lakes can slow surface drying, particularly in humid conditions.
- West-facing aspect means no morning sun to aid early drying — the boulders only catch afternoon and evening sun, which is limited in early April when the sun angle is still relatively low.
- Being roadside at 200m with partial wind exposure, moderate westerly winds will help surface drying when rain stops, but the SW winds today are driving further moisture onto the west-facing surfaces.
- The flat grassy landings around the boulders will be saturated and muddy after 54mm in the last week, creating additional slip hazards on approaches and landings.
Warnings
2
- Wet rhyolite is extremely slippery — bouldering falls onto saturated grassy landings compound the injury risk.
- The prolonged wet pattern means hidden seepage and residual dampness may persist on sheltered faces even after brief dry spells.
Reasoning
With 33.3mm yesterday and 5.6mm today, the rock surfaces are currently wet; there has been zero dry time since the heavy rain event.
No meaningful drying has occurred — today's ongoing rain and 80% humidity with SW winds blowing moisture directly onto the west-facing rock prevent any evaporation.
Rhyolite is non-porous and not at risk of structural damage when wet, but the slippery surface presents a serious friction and safety concern for bouldering.
Early April in Snowdonia brings short and unreliable drying windows; the persistently wet pattern over the last month (210mm in 28 days) means the surrounding ground and any cracks or seepage lines remain thoroughly saturated.
Contributing Factors
6
33.3mm fell yesterday and 5.6mm today, leaving rock surfaces actively wet with no intervening dry period.
There have been no dry days leading into today, so no drying window has occurred since the last significant rain.
Humidity at 80% today and averaging 79% over the past week significantly slows surface evaporation on the rock.
The prevailing SW wind at 31.7 km/h is driving moisture directly onto the west-facing boulder surfaces rather than aiding drying.
Over 210mm in the last 28 days means the surrounding environment is thoroughly saturated, contributing to persistent dampness and potential seepage.
Rhyolite does not absorb water, so once rain stops and conditions improve, surface drying can be relatively quick.
Recommendations
3
- Do not climb today — the rock is wet and rhyolite becomes very slippery when damp, making bouldering particularly dangerous.
- Monitor conditions for a dry window; the boulders could become climbable within a few hours of sunshine and breeze if rain fully stops, but today's forecast does not support that.
- Consider nearby indoor climbing walls (e.g. Beacon Climbing Centre in Caernarfon) as an alternative while waiting for conditions to improve.
Do Not Climb
92%
3 days ago
The RAC Boulders are currently wet and unsuitable for climbing. Today has seen 25.7mm of heavy rain with high humidity, and the preceding weeks have been extremely wet with nearly 200mm in 28 days — the rock surfaces will be thoroughly soaked and greasy.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit at roadside level near Llynnau Mymbyr and the surrounding boggy ground retains moisture, contributing to a damp microclimate that slows surface drying even on non-porous rhyolite.
- The west-facing aspect means the boulders only receive afternoon and evening sun, which in early April is limited and low-angled — morning dampness and condensation can linger well into the afternoon.
- Several problems on the lower boulders closest to the lake can develop a thin film of moisture from lake-effect humidity, particularly in calm conditions after rain.
- The grassy landings become waterlogged after sustained rainfall like this and may be slippery and unsuitable for safe spotting.
Warnings
2
- Rhyolite becomes dangerously slippery when wet — friction loss is severe and falls are likely on even easy problems.
- Waterlogged grassy landings increase the risk of ankle injuries and reduce the effectiveness of crash pads.
Reasoning
With 25.7mm falling today on top of 42.9mm in the last 7 days and nearly 200mm over 28 days, the rock surfaces are thoroughly wet and will have standing water in features and crevices.
Zero consecutive dry days and strong SW winds today will begin to strip surface water, but the sheer volume of today's rainfall combined with 84% humidity means meaningful drying has not yet begun.
Rhyolite is non-porous and does not suffer structural damage from moisture, so there is no hold-breakage concern — the issue is purely friction and safety.
Early April in Snowdonia is a notoriously wet period; temperatures averaging 8°C with persistent high humidity significantly slow evaporation rates, and the spring sun angle provides limited drying power on a west-facing crag at 200m.
Contributing Factors
7
25.7mm of rain today means the rock is actively wet with no drying window whatsoever.
Nearly 200mm over 28 days with repeated soaking events means the surrounding ground is saturated and the local microclimate is persistently damp.
Humidity at 84% today severely limits evaporative drying even with moderate wind.
37 km/h winds from the SW will help strip surface water from exposed faces once rain stops, aiding eventual drying.
Max 6.7°C today provides very little thermal energy to drive evaporation from rock surfaces.
West-facing boulders receive only late afternoon sun in early April, limiting solar drying to a few hours at best.
Rhyolite does not absorb water so surface drying is relatively quick once conditions improve, unlike sandstone which requires days.
Recommendations
3
- Do not visit today — the boulders are actively wet and the rhyolite will be extremely slippery.
- Monitor conditions closely; the earliest realistic window may open on April 12th afternoon if rain stops and wind persists, but even then assess on arrival.
- Check that grassy landings have dried sufficiently before committing to problems — waterlogged ground makes spotting hazardous.
Do Not Climb
70%
4 days ago
The RAC Boulders have had a very wet recent period with 12mm of rain yesterday and 1.2mm today, giving zero consecutive dry days. Although rhyolite dries relatively quickly, the persistent high humidity, cool temperatures, and lack of any meaningful dry spell mean surfaces are likely still damp and friction will be compromised.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit roadside at lakeside level near Llynnau Mymbyr, and the proximity to the lakes elevates local humidity and can slow surface drying even on otherwise decent days.
- West-facing aspect means the boulders only receive afternoon and evening sun — morning sessions will find rock that has been in shade and damp overnight, with the best drying window being mid-afternoon onwards.
- Many of the problems here are slabs and friction-dependent lower grades (V0–V4), which are disproportionately affected by any residual surface moisture on rhyolite compared to steep overhanging lines.
- The grassy landings can become waterlogged after prolonged wet spells like this one, making pad placement and footing problematic even if rock surfaces appear dry.
Warnings
2
- Friction-dependent slab problems (common at V0–V4 here) will be particularly treacherous if any residual moisture remains — do not assume the rock is dry just because it looks dry.
- Heavy rain forecast for tomorrow (23.7mm) will reset any drying progress made today.
Reasoning
With 12mm falling on April 9th and 1.2mm today (April 10th), plus 191mm over the past 28 days and persistent humidity around 78%, the rock surfaces are almost certainly still damp or at least not reliably dry.
Zero consecutive dry days, moderate westerly wind at 24.5 km/h, and only afternoon sun exposure mean that while some surface drying will have occurred through the day, it is insufficient to confidently declare the rock dry — especially on shaded faces and lower sections.
Rhyolite is non-porous and does not suffer structural damage when wet; there is no risk of hold breakage or rock degradation from climbing in these conditions.
Early April in Snowdonia is a transitional period with unpredictable weather; the recent pattern of repeated wet fronts interspersed with brief dry windows is typical, and overnight temperatures near 3°C combined with high humidity slow evaporation significantly.
Contributing Factors
7
12mm fell yesterday and 1.2mm today, with no consecutive dry days recorded, leaving surfaces likely still wet or damp.
Average humidity of 78% over the past week significantly slows surface evaporation on the rock.
Partial wind exposure with 24.5 km/h SW winds today provides some surface drying effect, though not enough to compensate for the recent rain.
The W aspect catches afternoon sun which aids drying later in the day, but morning and early afternoon conditions will be worse.
Average temperatures around 8.6°C over the past week provide limited evaporative energy compared to summer conditions.
Rhyolite does not absorb water so only surface moisture needs to evaporate, meaning drying is faster than on sandstone or gritstone once rain stops.
191mm over 28 days indicates a saturated local environment with waterlogged ground and elevated ambient moisture, slowing overall drying.
Recommendations
3
- Wait for at least one full dry day with lower humidity before visiting; the forecast suggests April 14th may be the first realistic opportunity.
- If you do visit in the coming days, focus on late afternoon when the west-facing rock has had maximum sun and wind exposure, and test friction carefully on easy problems first.
- Check the grassy landings for waterlogging before placing pads — the prolonged wet spell will have saturated the ground around the boulders.
Do Not Climb
45%
5 days ago
Today has seen 2.3mm of rain on already-saturated ground following a very wet period, with high humidity (84%) and moderate westerly winds blowing directly onto the west-facing boulders. Although rhyolite dries quickly in good conditions, the combination of today's rain, high ambient moisture, and a persistently wet spring means surfaces are likely damp and friction will be poor.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The west-facing aspect means prevailing SW/W winds and rain hit the boulders directly, and today's 30 km/h westerly wind will drive moisture onto the climbing surfaces rather than aid drying.
- RAC Boulders sit in the Mymbyr valley corridor which funnels moist Atlantic air; humidity regularly stays high here even on nominally dry days, and overnight condensation is common at 200m in spring.
- The roadside location and flat grassy surroundings mean the base can become waterlogged after prolonged wet spells — the 220mm in the last 28 days will have saturated the ground, potentially wicking moisture onto lower boulder faces.
- The brief dry spell of April 6–8 was promising but overnight humidity rose to 99% and today's 2.3mm of rain has reset the drying clock on these surfaces.
Warnings
2
- Rhyolite becomes very slippery when wet — friction-dependent slab and mantel problems at RAC Boulders pose a real fall risk in damp conditions.
- Overnight humidity reached 99% and condensation may persist on shaded boulder faces well into the morning even if rain stops.
Reasoning
Today's 2.3mm of rain on top of 84% humidity means rock surfaces are currently wet or at best damp, negating much of the drying gained during the April 6–8 dry window.
The moderate W wind (30 km/h) blows directly onto the west-facing boulders, which in this case drives rain onto the faces rather than aiding evaporation; any drying will need a period of dry weather with lower humidity.
Rhyolite is non-porous and structurally sound when wet — there is no risk of hold breakage or rock damage, so the concern is purely about friction and safety.
Early April in Snowdonia is characterised by unstable Atlantic weather patterns; the 220mm over 28 days is typical of a wet spring, and reliable multi-day dry spells are uncommon until late May.
Contributing Factors
6
2.3mm of precipitation today has wetted rock surfaces that had only partially dried from previous rain on April 5.
Humidity at 84% today, following overnight readings of 95–99%, inhibits evaporation and may produce persistent surface dampness or condensation.
220mm of rain in the last 28 days has thoroughly saturated the surrounding ground and moss, creating a persistently moist micro-environment around the boulders.
Two essentially dry days with warm temperatures (up to 19°C) and lower humidity (58%) would have dried exposed surfaces, though this progress has been partially undone.
The prevailing westerly wind drives rain and moist air directly onto the main climbing faces, reducing drying effectiveness on the primary aspect.
Non-porous rhyolite sheds water quickly and only needs surface drying, meaning a few hours of sun and breeze could restore friction if rain stops.
Recommendations
3
- Wait for a sustained dry spell — the rock needs at least a full dry day with humidity below 75% before friction will be reliable on these boulders.
- If you visit today or tomorrow, bring a towel and test friction on easy low problems before committing to anything at grade; retreat if holds feel glassy.
- Consider nearby sheltered east-facing alternatives or indoor walls until the forecast improves after April 13.
Marginal — Assess Conditions
70%
6 days ago
After two full dry days with warm temperatures (up to 19°C) and low humidity, the rhyolite surfaces at RAC Boulders should be largely dry today. However, the preceding very wet period (41mm in the last 7 days, 222mm in the last 28 days) means some seepage and sheltered damp patches may persist, so a visual check on arrival is recommended.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- RAC Boulders sit in a valley floor setting near Llynnau Mymbyr where cold air pooling and lakeside humidity can keep surfaces damper than hilltop crags, particularly overnight and in early morning.
- The west-facing aspect means the boulders only receive direct sun from mid-afternoon onwards — morning sessions may encounter residual dampness on shaded faces and north-facing sides of blocks.
- Some boulders have horizontal breaks and top surfaces that can hold standing water after heavy rain; check landings and top-outs for residual moisture even when vertical faces appear dry.
- The roadside location in the Nant Gwryd valley channels prevailing SW winds effectively, which has aided drying over the last two days.
Warnings
2
- Rain is forecast from tomorrow (April 9) through to at least April 13, so today represents a narrow dry window — conditions will deteriorate significantly.
- Check for nesting bird restrictions at nearby crags if you plan to visit multiple venues; early April is within the peregrine nesting season.
Reasoning
Two consecutive dry days with peak temperatures of 19.2°C and 17.3°C, plus low humidity (down to 43% yesterday afternoon), should have evaporated surface moisture from the non-porous rhyolite, though the enormous cumulative rainfall (222mm in 28 days) raises the possibility of lingering seepage from the saturated ground and surrounding hillside.
The west aspect received good afternoon sun yesterday with moderate SE breezes and very low humidity (43–52%), providing excellent drying conditions; today's SW wind at ~18 km/h continues to assist, though humidity has risen to 80% this morning.
Rhyolite is non-porous and does not suffer structural weakening when wet — there is no risk of hold breakage from moisture.
Early April in Snowdonia is transitionally wet; the ground is thoroughly saturated from a very wet March, and temperatures are only moderate, meaning seepage from surrounding slopes may continue to affect some boulder bases and lower faces.
Contributing Factors
7
No measurable rain since April 6 (0.1mm trace), giving approximately 48 hours of drying on non-porous rock.
Yesterday reached 19.2°C with humidity as low as 43%, providing exceptional evaporative drying conditions for early April.
222mm of rain in the last 28 days and 41mm in the last 7 days means the ground and hillside are thoroughly saturated, increasing the risk of seepage onto boulder surfaces.
Humidity has climbed to 80% this morning with increasing cloud, reducing ongoing drying effectiveness compared to yesterday.
Rhyolite does not absorb water, so surface moisture evaporates quickly and there is no structural damage concern.
The W-facing boulders will catch afternoon sun today if cloud breaks, continuing to aid drying on the main climbing faces.
The forecast shows 4.3mm tomorrow and continued unsettled weather for the next 5 days, making today the best window before conditions deteriorate.
Recommendations
3
- Visit this afternoon to maximise the benefit of any sun on the west-facing surfaces; check friction carefully on the first few problems before committing to harder lines.
- Avoid problems with known seepage lines or those on the north-facing sides of boulders where damp may linger from the saturated ground.
- Bring a towel for drying holds and a brush — this is likely the best window before unsettled weather returns from tomorrow onwards.
Marginal — Assess Conditions
60%
8 days ago
After a very wet period, today marks only the second consecutive dry day with improving conditions — warm temperatures (14°C) and moderate southerly wind should be drying the rock well. However, given the extremely wet preceding weeks (243mm in 28 days) and light showers as recently as yesterday evening, some seepage and residual dampness in sheltered spots is likely, so on-site assessment is essential before climbing.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The RAC Boulders sit in a valley floor setting near Llynnau Mymbyr where cold air pooling and lake-proximity moisture can keep humidity elevated overnight, potentially causing condensation on rock surfaces even on nominally dry days.
- Several of the boulders have overhanging faces and north-facing sides that won't benefit from the west-facing afternoon sun, meaning sheltered faces may retain dampness longer than the sunny aspects.
- Roadside location and flat grassy landings mean ground moisture from the saturated turf can contribute to a damp microclimate around the base of the boulders.
- Being a bouldering venue with low-level problems, any residual surface moisture directly impacts safety — a slip on greasy rhyolite even at boulder height can cause injury on the flat landings.
Warnings
2
- Some boulder faces — particularly overhanging or north-facing — may still be damp and greasy despite sun-exposed surfaces appearing dry; test every hold before committing.
- The saturated grassy landings may be slippery — take extra care with pad placement and spotting.
Reasoning
The last significant rain was 2.2mm on April 5th (with a light 0.6mm shower at 17:00 yesterday), and before that 10.2mm on April 4th and 22.3mm on April 3rd — the rock surface has had roughly 18–20 hours of drying since the last trace of rain, but the preceding weeks have been exceptionally wet.
Today's warm southerly conditions (13.9°C, 73% humidity, 18 km/h wind) are favourable for drying the west-facing surfaces, and yesterday afternoon saw several hours of low humidity (60–65%) with moderate wind, meaning sun-exposed faces should be largely dry by this afternoon.
Rhyolite is non-porous and does not suffer structural weakening when wet — there is no risk of hold breakage or rock damage from climbing on damp surfaces, only friction loss.
Early April in Snowdonia is a transitional period with unreliable weather; the recent pattern of persistent SW frontal systems bringing heavy rain is typical, and the current dry window may be brief with more rain forecast from April 9th.
Contributing Factors
6
Over 44mm fell in the last 7 days and 243mm in the last 28 days, creating a thoroughly saturated environment around the boulders.
Today is forecast dry with 13.9°C, 73% humidity, and moderate southerly wind — good drying conditions for rhyolite surfaces, especially the west-facing aspects catching afternoon sun.
With only one consecutive dry day before today and a light shower at 17:00 yesterday, there has been limited cumulative drying time.
Non-porous rhyolite sheds water quickly and doesn't absorb moisture, so exposed surfaces can dry within hours given adequate wind and warmth.
Humidity rose to 89% overnight near the lake, meaning condensation may have formed on rock surfaces and any residual damp patches won't have dried until mid-morning.
Partial wind exposure and today's 18 km/h southerly breeze will help evaporate surface moisture through the day.
Recommendations
3
- Wait until mid-to-late afternoon when the west-facing surfaces have had maximum sun and wind exposure before attempting any problems.
- Carefully test friction on each boulder before committing — touch the rock surface and check for any greasy film, especially on lower sections near the damp grass.
- Prioritise the most exposed, sun-facing problems and avoid any shaded or north-facing sides of the boulders where moisture is likely to linger.
Do Not Climb
70%
9 days ago
The RAC Boulders have received significant rainfall over the past week (45.8mm in 7 days, nearly 244mm in 28 days), with 2.5mm of rain today and zero consecutive dry days. Despite strong westerly winds aiding surface drying, the persistent wet pattern and today's precipitation mean surfaces are likely damp and friction will be compromised.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The west-facing aspect means these boulders are directly exposed to the prevailing SW/W winds and rain that have dominated the last month, increasing surface wetting during storms but also aiding post-rain drying.
- Roadside boulders at ~200m in the Nant Gwryd valley can experience mist and low cloud rolling in from Llynnau Mymbyr, adding ambient moisture even between rain events — check for condensation on arrival.
- The flat grassy landings may be waterlogged after 244mm of rain in 28 days, which can create splash-back moisture on lower boulder faces and make pad placement uncomfortable.
- Some of the lower problems near the lake shore may retain seepage and damp patches longer than the upper boulders due to proximity to the water table and saturated ground.
Warnings
2
- Rhyolite becomes very slippery when wet — do not attempt slab or friction-dependent problems if any surface moisture is present.
- Saturated grassy landings increase the risk of slipping on approach and may reduce pad effectiveness.
Reasoning
With 2.5mm of rain today, 10.2mm yesterday, and 22.3mm the day before, rock surfaces are almost certainly wet or damp despite the strong 36 km/h westerly wind.
The west-facing aspect and strong W winds (36 km/h) will promote rapid surface evaporation once rain stops, but with rain falling today and no consecutive dry days, meaningful drying has not yet occurred.
Rhyolite is non-porous and does not suffer structural damage when wet — hold breakage is not a concern at this venue.
Early April in Snowdonia is a transitionally wet period with average temperatures around 7.5°C, which slows evaporation; the prolonged wet spell is typical for this time of year but conditions have been notably wetter than average.
Contributing Factors
7
2.5mm today following 10.2mm yesterday and 22.3mm two days ago means rock surfaces have had no opportunity to dry.
There have been zero consecutive dry days, indicating the rock has been repeatedly wetted with no sustained drying window.
243.8mm in 28 days means the surrounding ground is saturated, prolonging ambient moisture and potential seepage.
The 36 km/h westerly wind hitting the west-facing boulders directly will help strip surface moisture once precipitation stops.
Temperatures around 6°C today are cool but above freezing, providing limited evaporative potential.
Rhyolite does not absorb water so only surface moisture needs to evaporate, meaning drying can be rapid once rain ceases.
Average humidity of 86% over the past week and 73% today slows evaporation and may cause condensation on cold rock surfaces.
Recommendations
3
- Wait for at least one full dry day with wind before visiting; rhyolite dries quickly but needs a genuine rain-free window to shed surface moisture.
- If visiting tomorrow (April 6), arrive in the afternoon to allow any morning dampness to clear and check friction on an easy slab before committing to harder problems.
- The flat grassy landings will be waterlogged — bring extra pads and be prepared for muddy conditions underfoot.
Do Not Climb
90%
10 days ago
The RAC Boulders are currently wet and unsuitable for climbing. Today has seen 6.7mm of rain on top of 22.3mm yesterday and persistent wet weather over the past week (54.7mm in 7 days), meaning the rock surfaces will be saturated with standing water and zero effective drying time.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit at roadside level near Llynnau Mymbyr in a valley floor setting, meaning surrounding saturated ground and lake proximity keep ambient humidity high and slow surface drying.
- West-facing aspect means the boulders only receive afternoon and evening sun — in early April with cloud cover and rain, effective solar drying hours are very limited.
- Several of the lower boulders and those nearest the lake can retain puddles and seepage on top surfaces and in cracks for extended periods after heavy rain.
- The grassy landings will be waterlogged after 237mm in 28 days, creating slippery and muddy conditions underfoot even if rock surfaces were to dry.
Warnings
2
- Wet rhyolite is extremely slippery — do not attempt to climb on damp surfaces as friction loss is severe and sudden.
- Waterlogged grassy landings significantly increase the risk of ankle and knee injuries from even low-height falls.
Reasoning
With 6.7mm of rain today following 22.3mm yesterday and 54.7mm over the past week, the rock surfaces are actively wet with no meaningful drying period.
Zero consecutive dry days, high humidity (89%), and limited afternoon sun through cloud cover mean virtually no drying has occurred; the strong SW wind helps but cannot overcome continuous rain input.
Rhyolite is non-porous and does not suffer structural damage when wet, so there is no rock conservation concern — the issue is purely friction and safety.
Early April in Snowdonia is peak wet season transition; temperatures averaging 7.8°C and persistent Atlantic fronts from the SW mean prolonged damp conditions are typical and drying is slow.
Contributing Factors
7
6.7mm of precipitation today means rock surfaces are currently wet with no opportunity to dry.
54.7mm in the past 7 days and 237.8mm over 28 days has kept the entire site saturated with no meaningful dry window.
There has been no dry day run to allow surface moisture to evaporate, meaning even sheltered faces will be damp.
Average humidity of 87% over the past week severely limits evaporative drying even during rain-free hours.
44.6 km/h SW winds today provide some surface drying potential, but this is insufficient to overcome active precipitation.
Rhyolite does not absorb water so will dry relatively quickly once rain stops and conditions improve — but that window has not yet arrived.
Prolonged heavy rain will have left the grassy landings muddy and slippery, increasing the risk of injury on even easy problems.
Recommendations
3
- Do not climb today — the rock is wet and friction on rhyolite is poor when damp, making even easy problems hazardous.
- Target April 7th or later when a dry spell with warmer temperatures (up to 17°C) and lower humidity should allow the boulders to dry out properly.
- Check landings carefully even after rock surfaces dry — the grassy areas around the boulders will remain waterlogged for days after rain stops.
Do Not Climb
92%
11 days ago
With 24.5mm of rain today and 51mm over the past 7 days, the RAC Boulders will be thoroughly wet. Rhyolite becomes extremely slippery when wet, and with high humidity (91%) and no dry days accumulated, surface conditions are unsuitable for safe bouldering.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The RAC Boulders sit in the Mymbyr valley between Llanberis Pass and Capel Curig, a natural funnel for Atlantic weather systems that channels persistent SW rain directly onto the boulders.
- The west-facing aspect means the boulders receive no morning sun to aid early drying, and the low March/April sun angle limits effective afternoon drying even when skies clear.
- Roadside boulders at this altitude (200m) in the Ogwen/Capel Curig corridor experience some of the highest annual rainfall in Snowdonia, and drainage from surrounding slopes can keep the base and lower sections damp long after rain stops.
- Several problems on the larger boulders have known seepage lines and lichen patches that retain moisture and become treacherously greasy — these are the last surfaces to dry.
Warnings
2
- Wet rhyolite is extremely slippery and bouldering falls onto grass landings from greasy holds carry serious injury risk.
- The Mymbyr valley road can flood in prolonged wet spells — check road conditions before travelling to Capel Curig.
Reasoning
With 24.5mm falling today on top of an extremely wet month (243mm in 28 days), the rock surfaces will be saturated with standing water and runoff.
Zero consecutive dry days, high humidity (91%), and only partial wind exposure mean no meaningful drying has occurred; the west aspect receives limited spring sun hours for evaporation.
Rhyolite is non-porous and does not suffer structural damage when wet, so hold integrity is not a concern.
Early April in Snowdonia is firmly in the unsettled spring period with frequent Atlantic fronts; temperatures averaging 7.5°C provide minimal drying energy and overnight condensation/frost is likely.
Contributing Factors
6
24.5mm of rain today ensures all boulder surfaces are thoroughly wet with active runoff.
51mm in the past 7 days and 243mm over 28 days means the surrounding ground is waterlogged and ambient moisture levels are extremely high.
There has been no dry window to allow even initial surface drying of the rhyolite.
Average humidity of 85% over the past week severely inhibits evaporation even during rain-free hours.
Partial wind exposure from strong SW winds (33 km/h) offers some drying potential once rain stops, but cannot compensate while rain is actively falling.
Rhyolite does not absorb water, so once rain ceases and wind/sun arrive, surface drying can be relatively quick — but that window has not arrived.
Recommendations
3
- Do not visit today — the boulders will be wet and dangerously slippery; wait for a sustained dry spell.
- Monitor conditions for April 6th, which forecasts zero precipitation and lower humidity — this could be the first realistic window if the preceding days see limited rain.
- Bring a towel and brush if visiting after a dry spell, as lichen and seepage patches on several boulders will be the last to dry.
Climbing Outlook