Eryri has some of the wettest weather in England and Wales — a consequence of its position directly in the path of Atlantic depressions tracking northeast across the British Isles, and its mountain topography which forces moist air upward, cooling it to its dew point. The summit of Yr Wyddfa receives over 4,500mm of precipitation annually. The valley at Beddgelert receives around 2,000mm. London receives 600mm. Understanding this is not a reason to avoid Eryri — it's a reason to prepare properly.
Annual Rainfall and Cloud Cover
The upland areas of Eryri typically receive 3,000–4,500mm of rain a year. The summit of Yr Wyddfa is in cloud for roughly 300 days a year — on average, it's clear for only 65 days annually. This does not mean you will see cloud on 300 days; it means that any given day has a roughly 82% chance of the summit being obscured at some point. Clear summits are achievable in all months — you just need to be ready to move quickly when the weather window opens.
Season by Season
Spring (March–May)
Probably the best season for serious walkers. Days lengthen rapidly, crowds are manageable (except Easter), and the mountain vegetation begins to green. Snow can persist on north-facing cwms into April — sometimes May — which adds drama to the higher routes. Weather is highly variable but improving. The upland tarns begin to warm from their winter temperature of near-freezing, and the first ring ouzels arrive in March.
Summer (June–August)
Peak visitor season. The longest days — in June, there are 16 hours of daylight at this latitude — and the warmest temperatures. July and August are the most reliably settled months, but "settled" is relative: a high-pressure system over Britain will produce days of crystalline visibility and warmth; a slow Atlantic low will produce days of sustained rain, low cloud, and near-zero visibility on the summits. The mountains are at their most crowded. Book accommodation months ahead. Check forecasts carefully.
Autumn (September–October)
Many experienced Eryri visitors rate September and October as the best months. The summer crowds have largely departed, the heather is in bloom through September, the bracken turns amber in October, and the lowering autumn light gives the landscape a particular quality. Weather remains variable but Atlantic high pressure systems can produce extended settled spells. The first frosts arrive on the higher summits in October.
Winter (November–February)
Winter in Eryri is for experienced mountaineers. Snow can transform the mountains — the views from Yr Wyddfa on a clear winter day, with the full snowpack visible, are extraordinary — but the conditions demand winter skills and equipment. Ice axes and crampons are essential above the treeline when frozen ground is present. Avalanche risk exists on the steeper north-facing slopes, particularly after heavy snowfall or a rapid thaw-freeze cycle.
Reading the Forecast
The single most useful resource for anyone climbing Yr Wyddfa is the Met Office Mountain Weather forecast for Snowdon, available at metoffice.gov.uk. This gives summit temperature, wind speed and direction, precipitation probability, and cloud base height at three-hour intervals. Check it the evening before and again on the morning of your walk.
Cloud base height is the critical number: if the cloud base is above 1,000m, the summit should be clear. If it's at 800m, the summit will be in cloud and the temperature will feel significantly lower than the valley. If it's at 500m, most of the mountain will be in cloud — potentially poor visibility even on the lower paths.
What Conditions Mean for Your Plans
Strong winds (above 40mph at summit level) make ridge routes like Crib Goch genuinely dangerous. Rain makes all paths slippery and increases exposure risk. Low cloud reduces visibility to near zero above the cloud base, making navigation on the open hillside difficult even with a compass. Poor visibility is one of the leading causes of mountain incidents in Eryri — it turns a clear path into a confusing maze of sheep tracks.
The wisest approach: have a Plan B. If summit conditions look poor, plan a lower-level walk — Cwm Idwal, the Mawddach Trail, the Aberglaslyn gorge — that will still be rewarding in the conditions. Save the summit for when the forecast is good.
What to Wear: Always
Regardless of the valley forecast: waterproof jacket, waterproof trousers, warm mid-layer (even in August the summit temperature can be 5°C), hat and gloves. This is not overcaution — it's the baseline for any walk above the treeline in Eryri at any time of year.
Independently written — Snowdon.com