Pen Pumlumon Arwystli weather forecast.

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

A rough, clagged-in day on Pen Pumlumon Arwystli: summit wind broadly 10-35 mph, with gusts 35-45 mph early in the morning (strong winds). Thunderstorms are forecast from around midday into the evening. Avoid exposed summits and ridges during the risk period. High spate risk based on forecast rainfall. Burns and unbridged crossings may become difficult or impassable. Most likely from around 06:00 until around 01:00 the following day. Much calmer lower down - generally 5-15 mph in the valley, rising towards the tops. Cloud base mostly around 500–800 m through daylight. Expect clag for much of the day, though a brief clearance is possible during the afternoon. A persistently wet day is possible, with around 20-40 mm indicated; local totals could vary considerably.

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

Cloud-free timing: Around 33% early, falling to around 0% later.

A grey, cloudy day on Pen Pumlumon Arwystli: summit wind broadly 10-30 mph, with gusts 30-40 mph during the evening (strong winds). Thunderstorms are a significant hazard from early morning into the afternoon. Exposed summits and ridges are a poor choice while storms are nearby. The ground is likely to be wet after recent rain. Much calmer lower down - generally 5-15 mph in the valley, rising towards the tops. Cloud base around 400–700 m in the morning, then around 600–900 m around midday and 400–700 m by late afternoon. Expect clag for much of the day, though a brief clearance is possible early in the morning. Cloud is likely to hang lowest on western slopes; the eastern 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 20-26 mph, so treat the headline as mid-range.

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

A rough, clagged-in day on Pen Pumlumon Arwystli: summit wind broadly 20-40 mph, with gusts 45-55 mph during the evening (gale-force winds). A meaningful thunderstorm risk is indicated from the morning into the afternoon. Avoid committing to exposed ridges if storms begin to build. 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 00:00 until around 02:00 the following day. Much calmer lower down - generally 5-15 mph in the valley, rising towards the tops. Cloud base mostly around 400–700 m through daylight. Expect the top to stay in cloud for most or all of daylight, with no dependable break. Cloud is likely to hang lowest on southwestern slopes; the northeastern 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. Low confidence (Summit wind could be roughly 25-49 mph, which changes how difficult exposed walking may feel) - the summit peak could be anywhere from 25 to 49 mph; check again nearer the time.

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

Cloud-free timing: Cloudy early, clearing later.

A mixed day on Pen Pumlumon Arwystli: summit wind broadly 20-35 mph, with gusts 35-45 mph during the evening (gale-force winds). 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. Much calmer lower down - generally 10-20 mph in the valley, rising towards the tops. Cloud base around 400–700 m in the morning, then around 1400–1700 m around midday and 900–1200 m by late afternoon. Summit cloud should lift later, bringing a better chance of clear views. 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 up to around 2 mm indicated; timing and local totals remain uncertain.

Forecast confidence: Rain is possible, but forecast models differ by about 10 hours on when it arrives.

Cloud-free timing: Cloudy early, clearing later.

A wild day on Pen Pumlumon Arwystli: summit wind broadly 35-45 mph, with gusts 55-65 mph during the morning (storm-force winds). Much calmer lower down - generally 15-25 mph in the valley, rising towards the tops. Any cloud sits well above the tops (base 800-1500 m) - clear summits. Cloud is likely to hang lowest on western slopes; the eastern 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. Cold on top: air temperature broadly 6 to 10°C, feeling around 0 to 4°C in the wind - wrap up. Confidence moderate (Summit wind could be roughly 35-51 mph, which changes how difficult exposed walking may feel) - the summit peak could reasonably be 35-51 mph, so treat the headline as mid-range.

Forecast confidence: Rain is possible, but forecast models differ by about 13 hours on when it arrives.

Cloud-free timing: Cloudy early, clearing later.

A mixed day on Pen Pumlumon Arwystli: summit wind broadly 20-35 mph, with gusts 40-50 mph early in the morning (gale-force winds). 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 00:00 until around 17:00. Much calmer lower down - generally 10-20 mph in the valley, rising towards the tops. Any cloud sits well above the tops (base 700-1400 m) - clear summits. Cloud is likely to hang lowest on western slopes; the eastern 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. Bright spells with UV up to 5 - sunscreen on exposed skin. Confidence moderate (Summit wind could be roughly 25-36 mph, which changes how difficult exposed walking may feel) - the summit peak could reasonably be 25-36 mph, so treat the headline as mid-range.