Condition Analysis
AI-powered assessment using site data and 14-day weather history
The RAC Boulders are currently wet from heavy rain today (11.3mm) with ongoing showers through the morning, and the forecast shows a prolonged wet spell of 4+ days ahead with over 50mm expected. Rhyolite becomes extremely slippery when wet, making bouldering unsafe — especially at a venue popular with beginners.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The RAC Boulders are roadside and low-lying near Llynnau Mymbyr, so mist and lake-effect humidity can keep surfaces damp even after rain stops.
- West-facing aspect means the boulders only receive afternoon/evening sun, which today is blocked by 100% cloud cover, severely limiting any drying potential.
- This is a beginner-friendly venue (predominantly V0–V4), so slippery conditions are particularly dangerous for less experienced climbers who may not recognise marginal friction.
- The flat grassy landings can become waterlogged after sustained rain, reducing the effectiveness of crash pads and increasing the risk of ankle injuries on landing.
Warnings
2
- Wet rhyolite is dangerously slippery — do not attempt to climb even if the rock appears only slightly damp.
- Waterlogged grassy landings reduce crash pad stability and increase injury risk from falls.
Reasoning
The rock is currently wet from 11.3mm of rain today, with heavy showers through the morning (3mm/hr at 09:00–10:00) and another burst at 15:00, on top of a wet preceding week (20.7mm in 7 days).
With 100% cloud cover, humidity above 90%, very light winds (5–8 km/h), and the west-facing aspect receiving no direct sun today, meaningful surface drying is essentially impossible.
Rhyolite is non-porous and not at risk of structural damage from moisture, but surface friction is severely compromised when wet.
Late August in Snowdonia is entering a wetter pattern; the extended forecast shows no reliable dry window for at least 4–5 days.
Contributing Factors
6
11.3mm of precipitation today including intense morning showers means the rock surface is thoroughly wet.
The next four days forecast 22.6mm, 13.0mm, 10.3mm, and 7.9mm respectively — no drying window is available.
Humidity has been above 90% all day and is forecast to remain so, preventing evaporative drying even during dry spells.
Wind speeds today are only 5–12 km/h, insufficient to assist surface drying at this partially sheltered venue.
100% cloud cover throughout the day eliminates any solar drying, and the west-facing aspect would only benefit from late afternoon sun anyway.
Rhyolite does not absorb water so there is no structural damage risk, and it will dry relatively quickly once conditions improve.
Recommendations
3
- Do not climb today or in the coming days — the rock is wet and the forecast shows continuous rain through at least August 30th.
- Monitor conditions from August 31st onwards when precipitation drops to 1.4mm; if followed by the dry day forecast on September 1st, surfaces may become climbable by late afternoon on the 31st.
- If visiting the area during this wet spell, consider indoor alternatives such as the Beacon Climbing Centre in Caernarfon.
Previous Analyses
Likely Safe to Climb
88%
57 days ago
Three consecutive dry days with moderate wind and dropping humidity have allowed the rhyolite boulders to dry thoroughly after the wet spell ending August 21st. Today offers excellent afternoon conditions with low humidity (40–50%), warm temperatures, and a dry forecast through the day — ideal friction on the RAC Boulders.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit roadside at lake level and can collect overnight dew or mist from Llynnau Mymbyr — early morning sessions may find damp surfaces even after dry spells.
- West-facing aspect means the boulders only receive direct sun from early afternoon onwards; morning shade can slow drying of any residual moisture.
- Flat grassy landings can become saturated and slippery after wet periods — the recent 20mm over the past week may leave soft ground underfoot despite dry rock.
- Some lower problems near the lakeside may retain splashback or ground-level dampness longer than the more exposed higher boulders.
Reasoning
The last meaningful rain was 3.5mm on August 21st, followed by three full dry days with moderate winds, giving ample time for surface moisture to evaporate from non-porous rhyolite.
Moderate westerly-to-northwesterly winds on August 22nd (22 km/h) followed by lighter winds have provided good air circulation, and the west-facing aspect catches afternoon sun — surface drying should be complete.
Rhyolite is non-porous and does not absorb water, so there is no risk of structural weakening or hold breakage from the recent wet period.
Mid-to-late August offers long daylight hours and reasonable temperatures; today's 20°C peak and low humidity (40%) provide excellent friction conditions for volcanic rock.
Contributing Factors
5
No rain since a trace 0.0mm on August 22nd, with the last significant rain (3.5mm) on August 21st — more than sufficient drying time for non-porous rhyolite.
Humidity drops to 40–50% this afternoon with clear skies and 20°C, providing outstanding friction conditions.
Consistent 13–17 km/h easterly winds today help keep surfaces dry despite partial shelter.
Over 20mm fell in the preceding week (Aug 17–21), but three dry days and non-porous rock type mean surface effects have cleared.
Significant rain is forecast from August 26th onwards (up to 30mm on August 28th), which will close the current dry window.
Recommendations
3
- Head out this afternoon for peak conditions — humidity below 45% and afternoon sun on the west-facing boulders from around 13:00 onwards.
- Check ground conditions at the landings, as the grassy areas may still be soft from recent rain; bring a mat even for the easier problems.
- Make the most of today and tomorrow — a deteriorating weather front arrives Wednesday with heavy rain forecast through the weekend.
Marginal — Assess Conditions
70%
58 days ago
After a wet spell ending on the 21st (23.5mm in the last 7 days), two dry days with moderate wind should have cleared surface moisture from this non-porous rhyolite. However, humidity remains moderately high (77% today) and some sheltered or north-facing surfaces may retain dampness, so a visual check on arrival is prudent.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit near Llynnau Mymbyr at 200m and lake-proximity can sustain local humidity and morning mist, even when the wider forecast is dry.
- West-facing aspect means the boulders only receive afternoon and evening sun — east-facing or shaded surfaces may retain moisture longer after rain.
- Roadside location with flat grassy landings can mean damp ground conditions even when rock is dry, especially after prolonged wet spells; consider a tarp for pads.
- Lichen and moss can develop on less-trafficked problems at this venue, adding to friction loss on damp holds — inspect holds before committing.
Warnings
1
- Friction on rhyolite drops significantly when even slightly damp — do not trust holds that feel slick, even if they appear dry.
Reasoning
The last significant rain was 3.5mm on Aug 21, followed by two fully dry days; surface moisture on non-porous rhyolite should have evaporated, though high ambient humidity (77–79%) may slow full drying of sheltered faces.
Two dry days with moderate wind (12–22 km/h) and west-facing aspect receiving afternoon sun provide reasonable but not exceptional drying; the easterly/northerly winds of the last two days would not drive air directly across west-facing surfaces.
Rhyolite is non-porous and does not suffer structural weakening when wet — no hold breakage or rock damage risk from recent moisture.
Mid-to-late August in Snowdonia is prone to Atlantic weather systems bringing frequent rain; the recent wet spell is typical, and another is forecast from Aug 25 onwards.
Contributing Factors
6
No precipitation since Aug 21 gives non-porous rhyolite adequate time to shed surface water under normal conditions.
23.5mm fell in the preceding 7 days across multiple days (Aug 17–21), meaning repeated wetting of all surfaces including crevices and horizontal ledges.
Partial wind exposure with 11–22 km/h winds over the drying period aids surface evaporation on exposed faces.
Humidity averaging 83% over the last week and 77% today slows evaporation and can leave a thin moisture film on cooler surfaces.
West-facing surfaces receive afternoon sun which helps dry the primary climbing faces, though shaded or east-facing sides dry more slowly.
Proximity to Llynnau Mymbyr elevates local humidity and morning dew formation, which can re-wet surfaces overnight.
Recommendations
3
- Visit in the afternoon when the west-facing boulders have had maximum sun exposure and any morning dew has burned off.
- Test friction on a low, safe problem before committing to anything committing — if holds feel greasy, wait for more drying.
- Bring a tarp or extra pad protection as grassy landings near the lake are likely still damp from recent rain.
Marginal — Assess Conditions
65%
59 days ago
The last significant rain was yesterday (3.5mm on Aug 21st, following a wet spell of 23.8mm over the past week), with today being the first fully dry day. Rhyolite dries quickly on the surface, but with only one dry day, high humidity (81%), and moderate winds, some seepage or residual dampness in sheltered spots is likely — 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 roadside near Llynnau Mymbyr at 200m, and the lakeside setting can maintain higher local humidity and morning mist even on otherwise dry days.
- West-facing aspect means the boulders only receive afternoon and evening sun, so morning sessions may encounter lingering surface dampness that hasn't yet been dried by direct sunlight.
- The grassy landings around these low-level boulders can remain saturated after prolonged wet spells, potentially wicking moisture onto the base of problems.
- As a beginner-friendly venue (V0–V4), many problems rely on friction-dependent slab and low-angle moves where even slight dampness on rhyolite significantly reduces grip.
Warnings
2
- Rhyolite friction drops dramatically when even slightly damp — friction-dependent slabs and mantels can become dangerously slippery.
- Grassy landings may be sodden after the recent wet spell; check landing zones carefully and consider supplementary pads.
Reasoning
After a prolonged wet spell (23.8mm in 7 days ending Aug 21), only one full dry day has elapsed, and humidity remains elevated at 81%, so residual surface moisture in sheltered nooks and seepage spots is probable.
Moderate NW wind today (20 km/h) and the west aspect means direct sun only arrives in the afternoon; one dry day with partial wind exposure should clear most open surfaces but may not fully dry recesses or north-facing boulder faces.
Rhyolite is non-porous and does not suffer structural weakening when wet, so hold breakage is not a concern at this venue.
Late August in Snowdonia brings shorter days, increasing rainfall frequency, and cooling temperatures (average 14.3°C this week), which slow drying compared to peak summer conditions.
Contributing Factors
7
23.8mm fell over the past 7 days across multiple days (Aug 17–21), saturating the ground and boulder surfaces repeatedly.
Only today (Aug 22) has been rain-free, which is marginal drying time even for non-porous rhyolite given the volume of recent rain.
Humidity at 81% today and averaging 83% over the past week slows surface evaporation significantly.
NW wind at 20 km/h with partial exposure aids surface drying on exposed boulder faces.
Aug 23 is forecast dry with dropping humidity (76%) and light northerly winds, giving a second consecutive drying day.
West-facing boulders catch afternoon sun which helps dry surfaces, though mornings remain in shade.
Rhyolite does not absorb water so only surface moisture needs to evaporate, enabling relatively quick drying.
Recommendations
3
- Wait until afternoon when direct sun has had time to warm and dry the west-facing boulder surfaces before attempting any problems.
- Visually inspect and hand-test each boulder face before climbing — avoid any problems with visible dampness, dark patches, or green lichen that may be slick.
- Consider prioritising the most exposed, wind-facing boulder faces first, as sheltered or north-facing sides may retain moisture longer.
Do Not Climb
45%
60 days ago
The RAC Boulders have received significant rainfall over the past five days (20mm+), including 4mm today, with high humidity averaging 83% — the rock is likely still wet or damp on sheltered faces. While rhyolite dries relatively quickly, the persistent moisture and lack of any consecutive dry days mean surface friction cannot be relied upon right now.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit near Llynnau Mymbyr at 200m and can collect ambient moisture from the lake, prolonging dampness even after rain stops.
- West-facing aspect means the boulders only receive afternoon and evening sun, so north- and east-facing sides of individual blocks will dry significantly slower.
- Roadside location with flat grassy landings can retain ground moisture, and splash-up from wet grass can re-dampen lower sections of problems.
- As a beginner-friendly venue (V0–V4), many visitors may lack experience judging marginal friction conditions on volcanic rock — extra caution is warranted.
Warnings
2
- Rhyolite becomes very slippery when wet — the excellent friction this rock is known for disappears entirely on damp surfaces, creating a serious slip and fall risk.
- Bouldering pads on wet grass can shift unexpectedly; ensure spotters are attentive and pads are well-placed.
Reasoning
With 4mm of rain today and 20+ mm over the preceding four days, the rock surfaces are almost certainly wet or at least damp, particularly on sheltered and north-facing faces of the boulders.
Zero consecutive dry days and moderate NW wind today provide some surface drying, but the west aspect limits direct sun to afternoon hours, and the high humidity (78%) significantly slows evaporation.
Rhyolite is non-porous and structurally unaffected by moisture — there is no risk of hold breakage or rock damage from climbing when damp.
Mid-to-late August in Snowdonia brings increasingly unsettled Atlantic weather patterns, and the recent spell of persistent rain and high humidity is typical; temperatures are moderate but not warm enough to accelerate drying rapidly.
Contributing Factors
6
Over 20mm has fallen in the past five days (Aug 17–21) with 4mm today, leaving surfaces wet.
There has been no full dry day to allow thorough surface drying across all aspects of the boulders.
Average humidity of 83% over the past week significantly slows evaporation from rock surfaces.
Rhyolite does not absorb water, so only surface moisture needs to evaporate — drying is faster than on porous rock types.
West-facing boulders receive afternoon sun which helps drying, but morning shade and north-facing sides of blocks will remain damp longer.
Partial wind exposure at 200m with 15–17 km/h winds aids surface evaporation when rain stops.
Recommendations
3
- Wait for at least one full dry day with moderate wind before visiting — the forecast suggests Aug 24 may offer the first genuinely dry window.
- If you do visit in the coming days, test friction carefully on low-consequence problems before committing to anything at height.
- Focus on the most sun-exposed, west-facing faces during afternoon hours if conditions are marginal, and avoid shaded or north-facing sides of boulders.
Do Not Climb
90%
61 days ago
The RAC Boulders are currently wet following 12.6mm of rain today (with showers continuing into the afternoon) on top of a very wet preceding week (27.2mm in 7 days). Rhyolite becomes dangerously slippery when wet, and conditions are not suitable for climbing today.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit roadside at 200m beside Llynnau Mymbyr and can accumulate moisture from lake-effect humidity, prolonging surface dampness even after rain stops.
- West-facing aspect means afternoon/evening sun only — with heavy cloud cover today (80–100%), there will be negligible solar drying.
- Flat grassy landings can become saturated and slippery after prolonged wet spells, adding to the risk for boulderers even if the rock surface starts to dry.
- Being a beginner-friendly venue (V0–V4), many visitors may lack experience judging friction on damp rhyolite — extra caution is warranted.
Warnings
2
- Wet rhyolite is extremely slippery — do not attempt problems even if the surface appears to be drying; friction can be deceptively poor.
- Saturated grassy landings increase the risk of slipping on approach and on fall zones around the boulders.
Reasoning
The rock is currently wet from 12.6mm of rain today, with significant showers as recently as 16:00, following a prolonged wet spell (8.9mm on Aug 18, 2.7mm on Aug 19).
With overcast skies (90–100% cloud), high humidity (74–94%), and the west-facing aspect receiving no meaningful sun today, surface drying will be minimal; the rock will remain damp into the evening.
Rhyolite is non-porous and not at risk of structural damage from moisture, but surface friction is severely compromised when wet.
Mid-August in Snowdonia often brings Atlantic frontal systems; the current wet spell is typical, and the forecast suggests improvement from August 22 onward.
Contributing Factors
5
12.6mm of precipitation today with showers continuing through mid-afternoon means the rock is thoroughly wet.
Over 27mm in the last 7 days with rain on 4 of the past 5 days has kept surfaces persistently damp.
Humidity of 74–94% and near-total cloud cover today severely limit evaporative drying.
Winds of 10–19 km/h provide some air movement but the west-facing boulders are partially sheltered from northwesterlies, limiting drying benefit.
A dry spell is forecast from August 22 with lower humidity and dropping to 72% by Aug 24, which should allow thorough drying.
Recommendations
3
- Do not climb today — the rock is wet and slippery; wait for the dry spell forecast from August 22.
- If visiting on August 22, check for residual dampness in sheltered cracks and north-facing sides of boulders before committing to problems.
- From August 23 onward conditions look much more promising — plan sessions for afternoon when any residual morning dew has cleared.
Do Not Climb
85%
62 days ago
The RAC Boulders are currently wet following significant rain over the past three days (19.5mm from Aug 17–19), with further showers forecast through today and into tomorrow. Although rhyolite dries relatively quickly, ongoing precipitation and high humidity (85%) mean surfaces will remain slippery and unsuitable for safe bouldering today.
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 can accumulate pooled water on flat tops and in seams, requiring visual inspection even after apparently dry spells.
- West-facing aspect means the boulders only receive afternoon and evening sun — morning sessions after overnight rain will find rock still damp, and today's cloud cover (often 90%+) limits solar drying.
- As a beginner-friendly venue (V0–V4), many visitors may be less experienced at judging friction on damp rhyolite — extra caution is warranted as even a thin moisture film dramatically reduces grip.
- The grassy landings can become saturated and slippery after prolonged wet weather, increasing the risk of ankle injuries on otherwise straightforward problems.
Warnings
2
- Wet rhyolite is extremely slippery despite its normally excellent friction — do not be tempted by brief dry gaps today.
- Grassy landings will be saturated and slippery after 20mm of rain in three days; pad placement and spotting need extra care even once rock dries.
Reasoning
Heavy rain on Aug 18 (8.9mm) and today (7.9mm, mostly falling as a 3mm burst at 07:00 and additional showers) means rock surfaces are currently wet with no meaningful dry window yet achieved.
Although rhyolite is non-porous and can dry within hours given sun and wind, today's persistent cloud cover (63–100%), high humidity (59–96%), and intermittent showers prevent effective drying even with moderate SW winds around 17 km/h.
Rhyolite does not suffer structural weakening when wet; the risk is entirely friction-based — wet volcanic rock is dangerously slippery despite its normally excellent grip.
Mid-August offers long daylight hours and reasonable temperatures (~16°C), but the current unsettled spell with SW airflow is typical of Atlantic weather patterns that can persist for several days in Snowdonia.
Contributing Factors
6
Nearly 20mm has fallen in the past three days (Aug 17–19), with the heaviest bursts today at 07:00 (3.0mm) ensuring surfaces are freshly wet.
Further light showers are forecast at 16:00 and 17:00 today, preventing any sustained drying window from developing.
Humidity remains 67–96% through the day, severely slowing surface evaporation even during the brief drier midday period.
Partial wind exposure with 16–19 km/h SW winds provides some air movement to assist surface drying during any rain-free gaps.
Heavy cloud cover (63–100%) blocks the afternoon sun that the west-facing boulders rely on for effective solar drying.
A further 10.7mm is forecast for Aug 20, meaning conditions will worsen before they improve.
Recommendations
3
- Do not climb today — the rock is wet and further showers are expected this afternoon.
- The earliest realistic session is the afternoon of August 22 if the forecast 0.6mm is negligible and some drying occurs, but visually check all surfaces before committing.
- Target August 23–24 for the best conditions this week, when two consecutive dry days with lower humidity should allow thorough drying.
Do Not Climb
88%
63 days ago
The RAC Boulders are currently wet from overnight and early-morning rain (6.5mm today), with 100% cloud cover preventing effective drying and humidity remaining very high (79–96%). Tomorrow and the following days bring further rain, so conditions are not suitable for climbing today or in the near term.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit roadside at 200m in the Mymbyr valley, where moisture can pool and mist linger even when higher crags are clearing.
- West-facing aspect means the boulders only receive afternoon/evening sun, and with 100% cloud cover forecast all day, no direct solar drying will occur.
- Flat grassy landings can become boggy and slippery after sustained wet weather, adding to the risk for beginner-friendly low problems.
- Being a popular beginner venue, polish on lower-grade holds reduces friction further when damp — extra caution is warranted.
Warnings
2
- Rhyolite becomes very slippery when wet — friction-dependent slab and wall problems are genuinely dangerous in these conditions.
- Wet grassy landings increase the risk of slipping on the approach and when spotting — take care even if not climbing.
Reasoning
The rock is wet from 6.5mm of rain today (most falling overnight to early morning), following a period of intermittent showers over the past two weeks totalling nearly 46mm.
With 100% cloud cover, humidity above 77%, and only moderate westerly wind, surface drying will be minimal — rhyolite can dry quickly in sun and breeze, but neither is available today.
Rhyolite is non-porous and not at risk of structural damage from moisture; the concern is purely friction loss on wet or damp surfaces.
Mid-August should offer reasonable drying conditions, but an unsettled Atlantic weather pattern is delivering persistent frontal rain and high humidity, suppressing any useful drying windows.
Contributing Factors
5
6.5mm fell today with most arriving overnight, and further showers are forecast through to August 21st.
Humidity has been 77–98% throughout today, severely inhibiting surface evaporation on the rock.
100% cloud cover all day eliminates any solar heating that would accelerate drying of the west-facing boulders.
Westerly wind at 14–26 km/h provides some air movement across these partially exposed boulders, but at high humidity its drying effect is negligible.
Rhyolite does not absorb water, so once surface moisture evaporates the rock will be fine — but that surface moisture is not evaporating today.
Recommendations
3
- Wait for the dry spell forecast from August 22nd onwards before visiting — two consecutive dry days should allow the boulders to dry fully.
- If you are in the area, use the time to scope problems and check landings rather than climbing on slick rock.
- Bring a towel and brush for August 22nd/23rd, as seepage from overhanging faces and mossy areas may persist even after the surface dries.
Marginal — Assess Conditions
55%
64 days ago
Light rain earlier today (0.6mm total, mostly around 03:00 and 12:00) followed by a drying afternoon window with dropping humidity and moderate wind; rhyolite surfaces should be drying but may retain dampness in sheltered spots. The coming week looks persistently wet with rain forecast every day through the 22nd, so this afternoon may be the best window for several days.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- The boulders sit roadside near Llynnau Mymbyr and can collect mist and condensation from the lake, especially on humid mornings — even without rain the rock can feel damp.
- West-facing aspect means afternoon and evening sun is the primary drying driver, and the 14:00–18:00 window today shows the best conditions with clearing skies and lower humidity.
- Some lower boulders near the lakeside grass can retain moisture at the base and on north-facing overhangs longer than sun-exposed faces.
- As a beginner-friendly bouldering venue with flat landings, wet or greasy conditions are especially risky for less experienced climbers who may not recognise subtle dampness on slab problems.
Warnings
2
- Rain is forecast from tomorrow through at least the 22nd — conditions will be worse than today for most of the coming week.
- High overnight humidity (94–98%) means early morning visits will likely encounter condensation on the rock even without rain.
Reasoning
Light rain at 03:00 (0.2mm) and 12:00 (0.4mm) today means surface moisture is likely present, though the afternoon drying window from 14:00 onward with humidity dropping to 74–75% and moderate SW wind should clear most exposed surfaces.
The west-facing aspect catches afternoon sun, and with winds around 13–15 km/h from the SW through the afternoon, exposed rhyolite surfaces should dry within 1–2 hours of the last rain, though sheltered faces will lag behind.
Rhyolite is non-porous and does not suffer structural weakening when wet, so there is no hold-breakage concern — the risk is purely friction loss on damp surfaces.
Mid-August in Snowdonia brings long daylight hours and reasonable temperatures (18°C), but the current spell of unsettled Atlantic weather with high humidity is typical and limits drying potential.
Contributing Factors
6
0.6mm total precipitation today including a 0.4mm shower around midday means surfaces were recently wetted.
Dry forecast from 13:00 onward with humidity dropping to 74% and moderate wind should allow exposed surfaces to dry by mid-afternoon.
Daily average humidity of 87% and overnight values exceeding 94% slow evaporation and risk condensation on the rock.
Cloud cover drops to 66% by 15:00 and the west aspect should catch some afternoon sun to accelerate surface drying.
4.6mm forecast tomorrow and 19.4mm total over the next 5 days means conditions will deteriorate significantly after today.
Rhyolite does not absorb water so only surface moisture needs to evaporate, allowing faster drying than porous rock types.
Recommendations
3
- If visiting today, aim for the 15:00–18:00 window when humidity is lowest and any afternoon sun will have had time to dry exposed west-facing surfaces.
- Physically touch the rock and test friction on easy moves before committing to harder problems — greasy rhyolite can feel deceptively grippy until you load a hold.
- Given the wet forecast for the coming week, consider this afternoon as your best opportunity and have an indoor alternative planned if surfaces remain damp on arrival.
Marginal — Assess Conditions
62%
65 days ago
The boulders have had an excellent dry spell from August 11–15 following earlier rain, but today's 0.5mm of light precipitation and rising humidity introduce some uncertainty. Rhyolite dries quickly and the rock should be fine for climbing if surfaces are visually dry, but a wet week ahead means today or early tomorrow may be the last good window.
Based on weather conditions only — does not cover bird nesting restrictions or other access issues.
- RAC Boulders sit at roadside near Llynnau Mymbyr and can collect splash and run-off from the A4086; some boulders closer to the road may retain dampness longer than those further away.
- The west-facing aspect means the boulders only receive afternoon and evening sun — morning sessions may encounter lingering dew or condensation, especially with humidity around 79–86%.
- Some of the lower boulders near the lake shore can be affected by ground moisture wicking up, particularly after prolonged wet spells like the one from late July.
- The flat grassy landings can become boggy after sustained rain, which may affect pad placement and safety for the wetter days ahead.
Warnings
1
- An extended wet spell is forecast from Aug 18–21; do not climb on wet rhyolite as friction loss creates a significant slip hazard, especially on the slab and friction-dependent problems.
Reasoning
Today saw only 0.5mm of light precipitation after five consecutive dry days (Aug 11–15), so surfaces are likely mostly dry but may have localised damp patches, particularly in sheltered or shaded areas.
The preceding five dry days with warm temperatures (up to 29°C on Aug 12) and moderate SW winds would have thoroughly dried the rock from the Aug 4–5 heavy rain; today's trace rain on non-porous rhyolite should evaporate within hours given 14 km/h winds.
Rhyolite is non-porous and not susceptible to structural weakening from moisture; there is no risk of hold breakage from climbing on damp rock.
Mid-August in Snowdonia offers long daylight hours and reasonable temperatures, but an incoming Atlantic frontal system from tomorrow onward will bring several days of rain and high humidity, limiting the climbing window.
Contributing Factors
5
Five fully dry days (Aug 11–15) with high temperatures up to 29°C provided excellent drying conditions for the rhyolite surfaces.
0.5mm recorded today breaks the dry streak and may leave trace surface moisture, though this is minimal on non-porous rock.
The forecast shows 5.0mm tomorrow (Aug 18) through to Aug 21, meaning conditions will deteriorate significantly from tomorrow onward.
Current 14 km/h SW winds aid surface drying, but humidity at 79% and rising to 86% tomorrow will slow evaporation and may cause condensation.
Afternoon sun on the west-facing boulders will help dry any trace moisture from today's light rain by mid-to-late afternoon.
Recommendations
3
- If climbing today, wait until mid-afternoon when the west-facing aspect catches sun and any trace surface moisture from this morning's rain has evaporated.
- Physically touch-test rock surfaces before committing to problems — rhyolite becomes noticeably slippery when even slightly damp.
- Consider prioritising today's session as conditions will deteriorate from Aug 18 onward with several days of forecast rain; the next reliable window may not arrive until Aug 22 or later.
Climbing Outlook