Glyder Fawr to the Bannau, Wales
Glyder Fawr was on the edge of a Likely area the night before, and Very likely by morning. The webcam was stuck in cloud, but Morgan and Neil were up above it.
Read the forecast checkBannau Brycheiniog / Brecon Beacons
Pen y Fan cloud inversion forecast. Next 24 hours.
Next 24 hours
Unlikely
Nothing forming around Pen y Fan right now. We’ll email you when that changes.
Captured 20 Oct, 21:07 BST · model rating, not a literal probability
Local outlook
Pen y Fan over the next 24 hours
Very likely
Likely
Possible
Purple dot: Pen y Fan
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Checked against what happened
Our forecasts, checked
We save each forecast before dawn, then compare it with dated photos of what happened. The nearest check to Pen y Fan so far is Cadair Idris, about 100 km north.
Yr Wyddfa, Wales
By the night before, Yr Wyddfa was Very likely. The summit webcam and a first-hand report both show it above a cloud sea across Eryri.
Read the forecast check
Cadair Idris, Wales
Cadair Idris stayed inside the area in 11 of our 12 updates. Photos from Tyrrau Mawr, other reports and satellite images all point to a cloud inversion across Eryri.
Read the forecast checkWe’ll publish misses and uncertain calls too, as the record grows.
Browse all forecast checksWhat your free alert looks like
We tell you where and when to look.
When a cloud inversion looks likely near Pen y Fan, WeatherDuck emails you up to 24 hours ahead, so you’ve time to check the route and set an alarm.
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WEATHERDUCK ALERT
Likely cloud inversion
Pen y Fan area
Best window05:00–08:00
Conditions are lining up for a cloud inversion. Check the latest forecast before you set off.
Example email · values are illustrativeLocal inversion guide
When can you see a cloud inversion at Pen y Fan?
The best chance comes when colder, moist air settles on low ground beneath warmer, drier air, winds stay light and the cloud top remains below your viewpoint.
Pen y Fan stands above the Usk valley, where cold air drains off the Beacons and pools overnight around Brecon and Talybont-on-Usk. The classic cloud sea forms when that valley layer stays below the summit ridge with drier, clearer air above.
Fog along the Usk near Brecon is a good early clue, but depth decides the morning. A shallow pool can leave even the lower ridges clear, while a deeper layer can swallow Pen y Fan and Corn Du completely.
Before you travel: the map shows the wider pattern across Bannau Brycheiniog / Brecon Beacons, not a promise for one summit. Check the latest wind, visibility and mountain forecast for your exact route.
See the forecast data and limitationsFind the warm lid
Look for warmer air sitting above a colder Usk valley. That lid is what traps overnight fog beneath the summit instead of letting it lift into hill cloud.
Check the Usk around Brecon
Moist air pooling between Brecon and Talybont-on-Usk feeds the cloud sea. Agreement across nearby forecast points beats one isolated fog patch.
Keep cloud below 886 m
The summit needs the cloud top comfortably below it with drier air above. If the layer builds deeper, Pen y Fan can sit inside the murk all morning.
Use the calmest window
Light winds along the valley help the pool survive the night. Dawn is usually the deepest, calmest moment before heating stirs the layers.
Plan beyond tomorrow
See the next two days
The public map stays focused on the next 24 hours. Premium extends the detailed inversion map, atmospheric profile and forecast window to two days.
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Browse other Bannau Brycheiniog & Black Mountains locationsQuick answers
Cloud inversion questions for Pen y Fan
Does fog in Brecon guarantee an inversion on Pen y Fan?
No. Valley fog is encouraging, but the cloud top must stay below the summit with clear air above. A deeper layer can cover Pen y Fan and Corn Du completely.
Is this a probability for the exact Pen y Fan summit?
No. The likelihood band is a regional model signal for Bannau Brycheiniog, supported by nearby captured forecast points. Local cloud can still differ from the wider pattern.
Does a Likely signal mean the path from Storey Arms is safe?
No. The outlook describes cloud structure, not wind, ice, visibility or route conditions. Check the full mountain forecast and local guidance before setting out.
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