Foel Cwm-Sian Llwyd weather forecast.

Forecast confidence: Thunderstorm timing is inherently uncertain and may shift by several hours.

Cloud-free timing: Around 0% early, improving to around 80% later.

A grey, cloudy day on Foel Cwm-Sian Llwyd: summit wind broadly 5-20 mph, with gusts 15-25 mph early in the morning (fresh and blowy). Thunderstorms are a significant hazard from the morning into the evening. Exposed summits and ridges are a poor choice while storms are nearby. Cloud base around 200–500 m in the morning, lifting to 500–800 m around midday and 700–1000 m by late afternoon. The top is likely to drift in and out of cloud, with the best chance of a view from late afternoon into the evening. Cloud is likely to hang lowest on southeastern slopes; the northwestern side should see somewhat higher bases and better breaks. Some rain is likely, with around 2-5 mm indicated; timing and local totals remain uncertain.

Forecast confidence: Thunderstorm timing is inherently uncertain and may shift by several hours.

A rough, clagged-in day on Foel Cwm-Sian Llwyd: summit wind broadly 10-25 mph, with gusts 20-30 mph during the evening (fresh and blowy). Thunderstorms are a significant hazard from around midday into the evening. Exposed summits and ridges are a poor choice while storms are nearby. There could be a spate risk based on forecast rainfall. Burns and unbridged crossings may rise quickly. Most likely from around 07:00 until around 23:00. Much calmer lower down - generally 0-10 mph in the valley, rising towards the tops. Cloud base around 200–500 m through the morning, lifting to 400–700 m by late afternoon. Expect the top to stay in cloud for most or all of daylight, with no dependable break. Cloud is likely to hang lowest on eastern slopes; the western side should see somewhat higher bases and better breaks. A persistently wet day is possible, with around 10-20 mm indicated; local totals could vary considerably.

Forecast confidence: Thunderstorm timing is inherently uncertain and may shift by several hours.

Cloud-free timing: Around 0% early, improving to around 100% later.

A mixed day on Foel Cwm-Sian Llwyd: summit wind broadly 15-25 mph, with gusts 25-35 mph during the afternoon (fresh and blowy). A meaningful thunderstorm risk is indicated from early morning into the evening. Avoid committing to exposed ridges if storms begin to build. The ground is likely to be wet after recent rain. Cloud base around 400–700 m in the morning, lifting to 600–900 m around midday and 700–1000 m by late afternoon. The top is likely to drift in and out of cloud, with the best chance of a view from around midday into the evening. Cloud is likely to hang lowest on northwestern slopes; the southeastern side should see somewhat higher bases and better breaks. Some rain is likely, with around 2-5 mm indicated; timing and local totals remain uncertain. Confidence moderate (forecast models agree on the walking impact of the wind) - the summit peak could reasonably be 18-26 mph, so treat the headline as mid-range.

Forecast confidence: Thunderstorm timing is inherently uncertain and may shift by several hours.

Cloud-free timing: Around 0% early, improving to around 60% later.

A grey, cloudy day on Foel Cwm-Sian Llwyd: summit wind broadly 10-25 mph, with gusts 20-30 mph early in the morning (fresh and blowy). Thunderstorms are a significant hazard from around midday into the evening. Exposed summits and ridges are a poor choice while storms are nearby. The ground is likely to be wet after recent rain. Cloud base mostly around 400–700 m through daylight. The top is likely to drift in and out of cloud, with the best chance of a view during the evening. Cloud is likely to hang lowest on southwestern slopes; the northeastern side should see somewhat higher bases and better breaks. Some rain is likely, with around 5-10 mm indicated; timing and local totals remain uncertain. Confidence moderate (Summit wind could be roughly 13-26 mph, which changes how difficult exposed walking may feel) - the summit peak could reasonably be 13-26 mph, so treat the headline as mid-range.

Forecast confidence: Thunderstorm timing is inherently uncertain and may shift by several hours.

Cloud-free timing: Around 33% early, improving to around 60% later.

A mixed day on Foel Cwm-Sian Llwyd: summit wind broadly 15-30 mph, with gusts 30-40 mph during the evening (strong winds). Thunderstorms are a significant hazard from early morning into the evening. Exposed summits and ridges are a poor choice while storms are nearby. The ground is likely to be wet after recent rain. There could be a spate risk based on forecast rainfall. Burns and unbridged crossings may rise quickly. Most likely from around 11:00 until around 02:00 the following day. Much calmer lower down - generally 5-15 mph in the valley, rising towards the tops. Cloud base around 400–700 m in the morning, lifting to 900–1200 m around midday and 1300–1600 m by late afternoon. The top is likely to drift in and out of cloud, with the best chance of a view from the morning into the evening. Cloud is likely to hang lowest on southwestern slopes; the northeastern side should see somewhat higher bases and better breaks. Some rain is likely, with around 5-10 mm indicated; timing and local totals remain uncertain. Confidence moderate (forecast models agree on the walking impact of the wind) - the summit peak could reasonably be 19-29 mph, so treat the headline as mid-range.

Forecast confidence: Forecast models disagree on whether meaningful rain reaches the hills during 10:00-16:00.

Cloud-free timing: Cloudy early, clearing later.

A mixed day on Foel Cwm-Sian Llwyd: summit wind broadly 20-35 mph, with gusts 40-50 mph around midday (gale-force winds). Much calmer lower down - generally 10-20 mph in the valley, rising towards the tops. Some rain is likely, with up to around 2 mm indicated; timing and local totals remain uncertain. Confidence moderate (Summit wind could be roughly 22-38 mph, which changes how difficult exposed walking may feel) - the summit peak could reasonably be 22-38 mph, so treat the headline as mid-range.