Cloud inversion forecast: Snowdonia
A cloud inversion traps fog in the valleys while summits sit in clear air and sunshine — the “sea of clouds” hillwalkers and photographers chase. Peakify analyses humidity, temperature profiles and cloud layers for every peak in the AI Mountain Explorer and scores the chance of an inversion. The mountains below currently have the best odds of putting you above the cloud.
Last analysed 18 Oct 2026. Best conditions are usually calm, clear nights after damp days — check each peak’s full forecast and sunrise time before an early start.
| Mountain | Elevation | Today | Next 7 days |
|---|---|---|---|
| Garnedd Uchaf Snowdonia | 925m | 29% Unlikely |
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| Tryfan Snowdonia | 918m | 28% Unlikely |
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| Pen yr Ole Wen Snowdonia | 978m | 26% Unlikely |
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| Elidir Fawr Snowdonia | 924m | 25% Unlikely |
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| Foel Grach Snowdonia | 975m | 25% Unlikely |
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| Foel-fras Snowdonia | 944m | 23% Unlikely |
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| Carnedd Dafydd Snowdonia | 1,044m | 22% Unlikely |
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| Carnedd Llewelyn Snowdonia | 1,064m | 21% Unlikely |
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| Castell y Gwynt Snowdonia | 972m | 19% Unlikely |
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| Crib y Ddysgl Snowdonia | 1,065m | 19% Unlikely |
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| Glyder Fach Snowdonia | 994m | 19% Unlikely |
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| Clawdd Coch Eryri (Snowdonia) | 931m | 18% Unlikely |
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| Crib Goch Snowdonia | 923m | 17% Unlikely |
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| Glyder Fawr Snowdonia | 1,001m | 17% Unlikely |
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| Y Garn Snowdonia | 947m | 17% Unlikely |
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| Carnedd Fach Eryri (Snowdonia) | 960m | 16% Unlikely |
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| Yr Elen Snowdonia | 962m | 13% Unlikely |
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| Yr Wyddfa - Snowdon Snowdonia | 1,085m | 13% Unlikely |
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Peaks in Snowdonia
154 summits. A dash means no inversion score in the last 36 hours: open the peak to run one.
| Yr Wyddfa - Snowdon | 1,085m | Snowdonia | 13% Unlikely |
| Crib y Ddysgl | 1,065m | Snowdonia | 19% Unlikely |
| Carnedd Llewelyn | 1,064m | Snowdonia | 21% Unlikely |
| Carnedd Dafydd | 1,044m | Snowdonia | 22% Unlikely |
| Glyder Fawr | 1,001m | Snowdonia | 17% Unlikely |
| Glyder Fach | 994m | Snowdonia | 19% Unlikely |
| Pen yr Ole Wen | 978m | Snowdonia | 26% Unlikely |
| Foel Grach | 975m | Snowdonia | 25% Unlikely |
| Castell y Gwynt | 972m | Snowdonia | 19% Unlikely |
| Yr Elen | 962m | Snowdonia | 13% Unlikely |
| Carnedd Fach | 960m | Eryri (Snowdonia) | 16% Unlikely |
| Y Garn | 947m | Snowdonia | 17% Unlikely |
| Foel-fras | 944m | Snowdonia | 23% Unlikely |
| Clawdd Coch | 931m | Eryri (Snowdonia) | 18% Unlikely |
| Garnedd Uchaf | 925m | Snowdonia | 29% Unlikely |
| Elidir Fawr | 924m | Snowdonia | 25% Unlikely |
| Crib Goch | 923m | Snowdonia | 17% Unlikely |
| Tryfan | 918m | Snowdonia | 28% Unlikely |
| Aran Fawddwy | 906m | Snowdonia | — |
| Y Lliwedd | 898m | Snowdonia | — |
| Y Lliwedd East Top | 893m | Snowdonia | — |
| Aran Benllyn | 885m | Snowdonia | — |
| Moel Siabod | 872m | Snowdonia | — |
| Mynydd Moel | 863m | Snowdonia | — |
| Arenig Fawr | 854m | Snowdonia | — |
| Llwytmor | 849m | Snowdonia | — |
| Arenig Fawr South Top | 837m | Snowdonia | — |
| Pen yr Helgi Du | 833m | Snowdonia | — |
| Foel-goch | 831m | Snowdonia | — |
| Tryfan Far South Peak | 831m | Snowdonia | — |
| Carnedd y Filiast | 821m | Snowdonia | — |
| Lliwedd Bach | 819m | Snowdonia | — |
| Moel Llechwedd | 817m | Snowdonia | — |
| Mynydd Perfedd | 813m | Snowdonia | — |
| Cyfrwy | 811m | Snowdonia | — |
| Bera Bach | 807m | Snowdonia | — |
| Y Foel Goch | 805m | Snowdonia | — |
| Foel Meirch | 799m | Snowdonia | — |
| Pen Llithrig y Wrach | 799m | Snowdonia | — |
| Bera Mawr | 794m | Snowdonia | — |
| Craig Cwm Amarch | 792m | Snowdonia | — |
| Moel Hebog | 784m | Snowdonia | — |
| Glasgwm | 779m | Snowdonia | — |
| Drum | 771m | Snowdonia | — |
| Moelwyn Mawr | 770m | Snowdonia | — |
| Mynydd Pencoed | 766m | Snowdonia | — |
| Gallt yr Ogof | 763m | Snowdonia | — |
| Drosgl | 757m | Snowdonia | — |
| Y Llethr | 756m | Snowdonia | — |
| Moel Llyfnant | 751m | Snowdonia | — |
| Diffwys | 750m | Snowdonia | — |
| Yr Aran | 747m | Snowdonia | — |
| Craig Eigiau | 735m | Snowdonia | — |
| Craig Cwm Silyn | 734m | Snowdonia | — |
| Rhobell Fawr | 734m | Snowdonia | — |
| Moel Eilio | 726m | Snowdonia | — |
| Carnedd y Filiast North Top | 720m | Snowdonia | — |
| Llechog | 720m | Snowdonia | — |
| Rhinog Fawr | 720m | Snowdonia | — |
| Cynefin Bryn Blew | 719m | Snowdonia | — |
| Arenig Fawr South Ridge Top | 714m | Snowdonia | — |
| Moelwyn Bach | 712m | Snowdonia | — |
| Rhinog Fach | 712m | Snowdonia | — |
| Trum y Ddysgl | 710m | Snowdonia | — |
| Garnedd-goch | 700m | Snowdonia | — |
| Allt-fawr | 698m | Snowdonia | — |
| Mynydd Mawr | 698m | Snowdonia | — |
| Mynydd Drws-y-coed | 695m | Snowdonia | — |
| Cnicht | 691m | Snowdonia | — |
| Cnicht North Top | 690m | Snowdonia | — |
| Craig Lwyd | 690m | Snowdonia | — |
| Craigysgafn | 690m | Snowdonia | — |
| Arenig Fach | 689m | Snowdonia | — |
| Carnedd y Ddelw | 686m | Snowdonia | — |
| Gwaun y Llwyni | 686m | Snowdonia | — |
| Mynydd Gwerngraig | 686m | Snowdonia | — |
| Pen y Brynfforchog | 685m | Snowdonia | — |
| Gau Graig | 684m | Snowdonia | — |
| Maesglase | 679m | Snowdonia | — |
| Creigiau Gleision | 676m | Snowdonia | — |
| Moel Druman | 676m | Snowdonia | — |
| Moel Cynghorion | 674m | Snowdonia | — |
| Carreg y Diocyn | 673m | Snowdonia | — |
| Ysgafell Wen | 672m | Snowdonia | — |
| Esgeiriau Gwynion | 670m | Snowdonia | — |
| Carnedd y Filiast | 669m | Snowdonia | — |
| Ysgafell Wen North Top | 669m | Snowdonia | — |
| Foel Cedig | 668m | Snowdonia | — |
| Tarren y Gesail | 667m | Snowdonia | — |
| Post Gwyn | 665m | Snowdonia | — |
| Dduallt | 663m | Snowdonia | — |
| Manod Mawr | 661m | Snowdonia | — |
| Cribin Fawr | 659m | Snowdonia | — |
| Foel Rhudd | 659m | Snowdonia | — |
| Y Groes Fagl | 659m | Snowdonia | — |
| Ysgafell Wen Far North Top | 659m | Snowdonia | — |
| Manod Mawr North Top | 658m | Snowdonia | — |
| Moel yr Ogof | 655m | Snowdonia | — |
| Pen y Brynfforchog North Top | 655m | Snowdonia | — |
| Mynydd Tal-y-mignedd | 653m | Snowdonia | — |
| Moelwyn Mawr North Ridge Top | 650m | Snowdonia | — |
| Pen y Boncyn Trefeilw | 644m | Snowdonia | — |
| Bryn Gwyn | 643m | Snowdonia | — |
| Diffwys West Top | 643m | Snowdonia | — |
| Gyrn Wigau | 643m | Snowdonia | — |
| Moel Lefn | 638m | Snowdonia | — |
| Clogwyn Llech Lefn | 637m | Snowdonia | — |
| Tarrenhendre | 634m | Snowdonia | — |
| Y Garn | 633m | Snowdonia | — |
| Creigiau Gleision North Top | 632m | Snowdonia | — |
| Gwaun Lydan | 632m | Snowdonia | — |
| Pen yr Allt Uchaf | 630m | Snowdonia | — |
| Stac Rhos | 630m | Snowdonia | — |
| Foel Gron | 629m | Snowdonia | — |
| Y Garn | 629m | Snowdonia | — |
| Moel Penamnen | 628m | Snowdonia | — |
| Foel y Geifr | 626m | Snowdonia | — |
| Moel y Cerrig Duon | 625m | Snowdonia | — |
| Pen y Castell | 624m | Snowdonia | — |
| Moel Ysgyfarnogod | 623m | Snowdonia | — |
| Craiglwyn | 622m | Snowdonia | — |
| Waun Camddwr | 622m | Snowdonia | — |
| Gallt y Wenallt | 620m | Snowdonia | — |
| Gallt y Daren | 619m | Snowdonia | — |
| Foel Boeth | 615m | Snowdonia | — |
| Cefn Gwyntog | 614m | Snowdonia | — |
| Foel Penolau | 614m | Snowdonia | — |
| Foel Goch | 613m | Snowdonia | — |
| Llechwedd Du | 613m | Snowdonia | — |
| Foel Goch | 611m | Snowdonia | — |
| Pen y Cerrig Duon | 611m | Snowdonia | — |
| Trum y Gwragedd | 611m | Snowdonia | — |
| Mynydd Graig Goch | 610m | Snowdonia | — |
| Tal y Fan | 610m | Snowdonia | — |
| Craig Fach | 609m | Snowdonia | — |
| Moel Meirch | 609m | Snowdonia | — |
| Craig Wen | 605m | Snowdonia | — |
| Mynydd Ceiswyn | 605m | Snowdonia | — |
| Y Gribin | 601m | Snowdonia | — |
| Foel Lwyd | 600m | Snowdonia | — |
| Foel Ddu | 591m | Snowdonia | — |
| Yr Arddu | 589m | Snowdonia | — |
| Moel Wnion | 580m | Snowdonia | — |
| Tryfan North Top | 577m | Snowdonia | — |
| Foel Rûdd | 573m | Eryri (Snowdonia) | — |
| Craig Stwlan | 569m | Snowdonia | — |
| Yr Orsedd | 559m | Snowdonia | — |
| Moel-ddu | 552m | Snowdonia | — |
| Cefn Cyfarwydd | 502m | Snowdonia | — |
| Cefn y Capel | 460m | Snowdonia | — |
| Moel Tryfan | 429m | Snowdonia | — |
| Mynydd Deulyn | 400m | Snowdonia | — |
| Moel y Dyniewyd | 382m | Snowdonia | — |
| Craig-y-garn | 363m | Snowdonia | — |
Cloud inversion forecast by area
What is a cloud inversion?
Normally the air gets colder as you climb. In a temperature inversion a layer of warm air sits on top of cold, damp air in the valleys, so fog and low cloud are trapped below and the summits stand in sunshine above a sea of cloud. Inversions are most likely after a calm, clear night following a damp day, often in autumn and winter, and they usually burn off by late morning, so go early.
How a cloud inversion forms
After a damp day the wind has dropped and the sky has cleared. The air in the valleys still holds plenty of moisture.
What if…
A sea of cloud is likely: calm, clear and damp.
Read it step by step
- A calm, clear evening. After a damp day the wind has dropped and the sky has cleared. The air in the valleys still holds plenty of moisture.
- Heat escapes to the sky. With no cloud overhead to act as a blanket, the ground radiates its warmth straight out to space, and the air touching it starts to chill.
- Cold air drains downhill. Chilled air is denser than the air around it, so it slides down the slopes like water and gathers on the valley floor.
- The inversion forms. A pool of cold air now fills the valleys with milder air above it. Normally it gets colder as you climb; tonight it gets warmer. That flip is the temperature inversion.
- Mist over the water. Lakes and wet ground give the cold air the last bit of moisture it needs, so wisps of mist form there first. If you are going up, this is when to set off, by head torch.
- Fog fills the valleys. The trapped air keeps cooling until it reaches its dew point. Its moisture condenses into tiny droplets, and the cold pool turns to fog. Climbing through it, you see nothing but grey.
- A sea of cloud. The warm layer above works like a lid, so the fog cannot rise through it. Summits higher than the lid break out into clear air and sunshine.
- The best hour on top. Low sun lights the cloud tops gold and the hills cast long shadows across them. Turn your back to the sun: your own shadow may land on the cloud inside a rainbow ring, a Brocken spectre.
- The sun gets to work. Sunlight warms the slopes and the ground beneath the fog. Rising thermals stir the air and start to break the lid.
- The inversion lifts. The cloud rises, thins and breaks apart, usually by late morning. Then it is an ordinary day again, until the next calm, clear night.
Cloud inversion or fog?
From the valley floor an inversion just looks like fog. The difference is what is above it: if the summit is higher than the top of the fog layer, you climb out of the grey into clear air. The chances here are for standing above the cloud from each summit.
New to inversions? Read what a cloud inversion is and how to catch one, or get an alert on your phone when your hills look likely with the Peakify cloud inversion app.
Out after dark too? See the aurora forecast for the UK and the astronomy calendar.
Browse mountains by area
How the cloud inversion forecast for Snowdonia works
What an inversion needs
Air gets colder as you climb. On a calm, clear night the ground loses heat, cold air drains into the valleys, and warmer air settles on top of it. If the valley air is damp enough, it condenses into fog, and the warm layer holds it down like a lid. Stand on a summit above that lid at dawn and you look across a flat sea of cloud.
How Peakify scores it
For each mountain, Peakify finds the lowest ground within 6 km of the summit, where fog would pool, and pulls an hourly forecast for the summit and that valley from Open-Meteo. It scores every hour from three hours before sunrise to two hours after and keeps the best.
Five ingredients build the score: a stable, layered atmosphere between about 750 m and 1,500 m, valley air close to saturation, dry air above the summit, overnight cooling in the valley, and a long night. Five checks then scale it: wind at summit height, overnight cloud, air pressure, wind in the valley, and the depth of the fog. Peakify estimates the fog top as the forecast boundary-layer height above the valley floor. Strong wind on the tops, or fog deeper than the summit is high, takes even a good setup close to zero.
How to read the table
The table ranks up to 40 peaks with a score from the last 36 hours, using today’s forecast. 70% and over is Excellent, 50 to 69% Good, and 30 to 49% Possible. Open a mountain for the full breakdown: the best hour, how long the inversion should last, which ingredients hold it back, a seven-day outlook and a confidence rating. Confidence is High when the ECMWF and Met Office models agree on a calm, clear valley at dawn, and Low when they disagree.
Limits
Read the percentage as a score of how well the ingredients line up. Forecast models work on grids 1 to 10 km across and can’t see into a narrow valley, so Peakify estimates the valley air from a coarser picture. Fog over a lake or in one side valley may not show. The table lists only peaks scored in the last 36 hours, so a quiet hill with a good setup can be missing until someone opens its page. And plan for the walk in: you’ll climb in the dark, through the fog, to reach the clear air.
Cloud inversion questions
Where in Snowdonia has the best cloud inversion forecast today?
The table at the top of this page ranks summits in Snowdonia by today's cloud inversion score, refreshed each morning from the latest forecast. Peaks that rise well above deep, sheltered valleys tend to score best, but the setup changes from day to day, so check again the evening before you go.
What is a cloud inversion?
A cloud inversion happens when a layer of warm air sits on top of cold, damp air in the valleys. Fog forms in the cold layer and can't rise through the warm one, so from a summit above it you look down on a flat sea of cloud.
When do cloud inversions happen in the UK?
Mostly in autumn and winter, on calm, clear nights under high pressure, often after a damp day. Long nights give the valleys more time to cool, and light winds let the cold air settle instead of mixing.
What time should I be on the summit?
Before sunrise. Peakify looks for the best hour between three hours before sunrise and two hours after, and each mountain page gives that time and the sunrise. Once the sun warms the valleys, the fog thins and lifts.
How high do I need to climb to see one?
Higher than the top of the fog. Peakify estimates the fog top from the forecast boundary-layer height above the lowest ground near the mountain and compares it with the summit. On a shallow fog morning a modest hill clears it. On a deep one, even a 900 m summit can stay in the murk.
How reliable is the cloud inversion forecast?
Use it as a guide and check again the evening before. Each mountain page shows a confidence rating: High when the ECMWF and Met Office models agree on whether the valley will be calm and clear at dawn, Low when they disagree.
Why isn't my mountain in the table?
The table ranks the 40 highest scores among peaks with a forecast from the last 36 hours. Peakify refreshes popular UK summits each morning and any other peak when someone opens its page, so open your mountain to score it.