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UK cloud inversion forecasts. Leave the fog in the valley.

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Sunlight above a sea of cloud flowing over a ridge below Skiddaw, photographed by Joss
Skiddaw cloud inversion · 17 December 2021

Our most recent inversions

Our Performance

Here’s how WeatherDuck performed across the three most recent cloud inversions in our published record. Each forecast was saved before the event, then compared with dated, independent evidence of what happened.

Archived cloud inversion forecast map for Tap o’ Noth, with the verified location marked
Very likely Forecast issued: 46 hours ahead

Tap o’ Noth, Aberdeenshire

The dawn forecast highlighted the area before a cloud inversion was independently photographed.

View Tap o’ Noth forecast check
Archived cloud inversion forecast map for Torridon, with the verified location marked
Likely Forecast issued: 42.9 hours ahead

Beinn Liath Mhòr, Torridon

The forecast highlighted the dawn window before an inversion was photographed below the ridge.

View Torridon forecast check
Archived cloud inversion forecast map for Cadair Idris, with the verified location marked
Very likely Forecast issued: 21 hours ahead

Cadair Idris, Eryri

A Very likely area covered southern Eryri before a cloud sea formed below the ridge.

View Cadair Idris forecast check

We’ll publish successful forecasts, false alarms, misses and uncertain outcomes as the record grows.

Browse all forecast checks

What your free alert contains

Your alert tells you where and when to look.

When the forecast looks promising near your chosen mountain area, WeatherDuck emails you up to 24 hours ahead, giving you time to check conditions and plan your trip.

  • One mountain area with your free account
  • Up to 24 hours of warning
  • Likely and Very likely signals
WEATHERDUCK ALERT

Very likely cloud inversion

Helvellyn area

Best window04:00–07:00

Conditions are lining up for a cloud inversion. Check the latest forecast before you set off.

Example email · values are illustrative

Forecast without an account

Try the free cloud inversion predictor

Search any UK location to see the latest forecast and viewing window.

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Latest inversion outlook

UK cloud inversion forecast: next 24 hours

A quick UK-wide view of monitored mountain areas. Search above for the timing and atmospheric evidence at a specific place.

Unlikely

No widespread inversion signal

Cloud inversions look unlikely across the monitored UK mountain areas in this forecast period.

Updated Covers to

Latest forecast loaded

  • Small, local or short-lived pockets of valley fog can still form.

Check your location

See timing, cloud heights and atmospheric evidence for your nearest valleys and summits.

See full forecast
Forecast notes

Could my summit be above the clouds?

Compare the forecast cloud-top height with your summit elevation. Cloud heights are estimates above sea level, and the actual cloud layer may sit higher or lower.

What do Likely and Very likely mean?

These bands describe the strength of WeatherDuck’s cloud inversion forecast signal. Very likely is the stronger signal; neither rating is a percentage chance or a guarantee of a clear summit.

Cloud inversion guide

What is a cloud inversion and how does it form?

A cloud inversion happens when cold, moist air becomes trapped beneath warmer air. When moisture in the cold layer condenses into fog or low cloud, valleys can fill with cloud while higher hills rise into clearer air. Seen from a summit, this becomes the familiar sea of cloud.

Cross-section of a cloud inversion: cold, moist air trapped under a warm lid fills the valley with fog, while two summits rise above the cloud top into clear sunlit air. A temperature profile alongside shows the air warming with height through the inversion before cooling again.
Air usually cools as height increases. During a temperature inversion a warmer layer sits on top instead, acting like a lid that traps cold, moist air below. Where that trapped air is damp enough it condenses into the sea of cloud, and any summit above the cloud top reaches clear air.

How does cold air become trapped in a valley?

After sunset, the ground loses heat and cools the air directly above it. Cold air is denser than warm air, so it tends to flow down slopes and gather in valleys, glens, hollows and sheltered basins. This movement is known as cold air drainage.

If the wider weather pattern is calm, the pooled air can remain in place for much of the night. Warmer air above limits mixing and keeps the cold pool close to the landscape. A valley can therefore become much colder than a nearby ridge even though the two places are only a short distance apart.

How does fog or low cloud appear?

Cooling air eventually reaches a temperature at which some of its water vapour begins to condense. This temperature is called the dew point. Tiny water droplets then form in the air, creating fog at ground level or a shallow sheet of low cloud across the valley.

A temperature inversion can exist without any visible cloud. If the trapped air is too dry, the warm lid may be present but the valley will stay clear. The classic sea of cloud needs both the layered temperature structure and enough moisture in the lower air.

Why can it be grey below but clear above?

The warm lid traps moisture in a shallow layer near the valley floor. The valley may then be misty and dull while the air above the cloud is warmer, drier and clearer. A hill that rises through the cloud top can reach sunshine even when communities below remain under fog.

This separation is what turns ordinary valley fog into a useful summit view. If moisture and cloud continue through the higher atmosphere, the result is more likely to be widespread hill cloud or overcast rather than a clean sea of cloud.

Cloud inversion or just fog?

Fog and cloud inversions are close relatives, and from inside the murk they can feel identical. The difference is what is happening above your head, and it decides whether a dawn start ends in sunshine or in damp grey.

The tell is the cloud top. A true inversion has a defined ceiling, with warmer, drier, clearer air above it and the summits standing proud of it.

Valley fog What you want Forms when cold air pools overnight and its moisture condenses.

This is the raw ingredient of a cloud sea, and the fog you want to see filling the valleys below you.

Radiation fog Also promising The wider version of the same process, forming over low ground on clear, calm nights.

It often burns off during the morning as the sun warms the ground.

Hill fog The impostor Simply cloud sitting on the high ground.

The summits are inside it, not above it. This is the classic disappointment: the valley webcam looks promising, but the tops never break clear.

Haar, or sea fog Easily mistaken Drifts in from the coast on a moist onshore breeze.

It can photograph exactly like an inversion from a distance, but there is often no warm lid above it, so the top is ragged and a summit that looks clear one minute is swallowed the next.

Freezing fog Handle with care Any of the above in sub-zero air, coating everything it touches in rime ice.

Beautiful above the cloud top, and a real hazard on paths inside it.

Why does the depth of cloud matter?

If moisture continues up through the atmosphere, there is no ceiling to break through, and what looks like a sea of cloud from the valley is really the bottom of a much deeper layer.

How does WeatherDuck check for this?

This is exactly what the forecast checks for you. It looks for temperature rising with height, moisture trapped beneath drier air, and a cloud top sitting below the summits. When the profile shows cloud continuing upwards instead, the score stays low, because that morning is hill fog, not a cloud sea.

Sources and further reading

Read the signs

How to predict a cloud inversion

There isn’t one magic forecast symbol. The most convincing setup is a group of clues that agree: cold, moist air pooled on lower ground, a warmer layer above it, light winds and a cloud top below your chosen viewpoint. Work through these six checks, then look again at the newest forecast before you travel.

  1. Choose a valley and a higher viewpoint

    Start with sheltered valleys, glens, hollows and basins where cold air can collect.

    Compare the forecast’s cloud-top estimate with the height of your ridge or summit, using metres above sea level for both. Nearby slopes can still sit in different cloud.

  2. Look for a calm, cooling night

    Clear spells allow the ground to cool more readily after sunset, while gentle low-level winds help colder air drain downhill and remain pooled.

    Thick cloud can slow the cooling, and stronger wind can stir the layers together.

  3. Check that the lower air is moist

    Look for high humidity, or for the air temperature and dew point to sit close together over lower ground.

    Damp soil, recent rain, rivers and lakes can add moisture. Dry valley air can produce an inversion without any visible cloud.

  4. Find the warmer layer above

    In the atmospheric profile, the chart showing temperature at each height, look for temperature increasing with height above the colder valley air.

    That warmer layer is the inversion, the lid that can limit mixing below. It is an important clue, but it cannot promise a sea of cloud on its own.

  5. Make sure the cloud stays below you

    A useful summit view needs moist air and cloud below, with clearer air above the layer.

    Compare the estimated cloud top with your viewpoint and look for drier air above. Deep cloud through summit level is a warning that you may simply be inside it.

  6. Check the conditions around dawn

    Your best chance is when low cloud stays below your viewpoint, the air above remains clear and winds stay light while you plan to be out.

    Check the latest cloud inversion and mountain forecasts before setting off, as conditions can change quickly.

Good signs

Calm air, moisture and cloud below you.
  • Clear spells and light winds overnight
  • Moist air pooled over lower ground
  • Temperature rising with height above the cold pool
  • Drier or clearer air above shallow cloud
  • Cloud top below the chosen viewpoint
  • The same signal across nearby places and updates

Warning signs

Wind, deep cloud or a changing forecast.
  • Strengthening or turbulent wind
  • Thick cloud throughout the night
  • Dry air over lower ground
  • Persistent rain or an approaching front
  • Cloud reaching summit level
  • A signal at only one place or one hour

Ready to check the setup?

Search any UK location to see the next 24 hours, the strongest viewing window and the atmospheric evidence behind the WeatherDuck band.

Check the cloud inversion forecast

Before you set the alarm

Cloud inversion forecast questions

Will there be a cloud inversion tonight in the UK?

Check the current UK outlook at the top of this page. It always shows the latest national cloud inversion signal for the next 24 hours, the monitored mountain regions worth watching and when the dataset was last updated. For a specific summit or valley, search the location to see its timing and atmospheric evidence.

Does a Likely or Very likely band guarantee a clear summit?

No. The bands describe the overall strength of the WeatherDuck forecast signal; they are not percentage chances or promises that a particular summit will be clear. Read the band alongside the viewing window, cloud-top estimate, wind and wider mountain forecast.

Is valley fog the same as a cloud inversion?

Valley fog can provide the cloud within an inversion, but fog alone does not guarantee a sea of cloud. The layer needs to remain below the viewpoint with clearer air above it. A temperature inversion can also form without visible cloud when the lower air is too dry.

How high do I need to climb?

The viewpoint needs to be above the actual cloud top, not merely above the valley floor. Any modelled cloud height is an estimate above sea level, and local cloud can sit higher or lower than forecast. Choose a safe viewpoint and never treat a modelled height as a route recommendation.

Can you see a cloud inversion without climbing a mountain?

You need to be above the cloud top, but that does not always mean a long climb. From inside the valley an inversion simply looks like fog or a grey sky. Some high roads, passes and smaller hills rise above shallow layers, which is why comparing the cloud-top estimate with your own height matters.

What time of day is best to see a cloud inversion?

Around dawn. The cold pool and its cloud are usually deepest at the end of a long night, and first light is also when the view is at its best for photography. Daytime heating then stirs the layers, so many inversions fade during the morning.

What time of year are cloud inversions most common in the UK?

Autumn and winter are the classic seasons. Long, clear and calm nights give valleys time to cool, and high pressure can hold the cold, foggy layer in place well into the day. Inversions can still form in spring and summer, but they are usually shallower and break up soon after sunrise.

How long does a cloud inversion last?

Anything from under an hour to several days. Most morning inversions fade as the sun warms the ground and wind mixes the layers. In deep winter valleys under settled high pressure, the cloud can survive all day, a pattern sometimes called anticyclonic gloom.

Why can the cloud inversion forecast change?

Small changes in wind, moisture, temperature and cloud depth can decide whether a valley pool forms or survives. The outlook changes as newer forecast information becomes available.

Where does the forecast work?

You can search any UK location. The national view summarises monitored mountain areas, while the full forecast shows the available outlook and atmospheric evidence for the searched place.

How often is the cloud inversion forecast updated?

WeatherDuck captures fresh forecast data throughout the day. The UK outlook shows when its current dataset was updated and when the forecast window ends, so check those times and the latest mountain forecast before travelling.

Is there a cloud inversion predictor app?

WeatherDuck works as a cloud inversion predictor in any browser, with nothing to install. Search a location for the latest outlook, add the site to your phone home screen for one tap access, and set a free email alert so a Likely forecast finds you first.

Popular inversion forecasts

Start with a wider region, or go straight to a popular mountain. Every page has its own fixed 24-hour map and terrain-specific guide to reading the inversion setup.

Regions

Use these wider fixed maps to compare valleys and basins before choosing a particular viewpoint.

Derbyshire and the South Pennines

Peak District

Follow the broader signal across Edale, Castleton, the Hope Valley and the surrounding high moorland.

Open the Peak District outlook

North Wales

Eryri / Snowdonia

Compare Capel Curig, Nant Gwynant and the Ogwen Valley across a wider view of Eryri’s mountain basins.

Open the Eryri outlook

Nationwide mountain view

Scotland

Scan the wider Highland pattern, with the single headline clearly labelled as the central Highlands regional signal.

Open the Scotland outlook

Popular mountains

These closer fixed maps use a tighter zoom and explain the cloud-height clues around each mountain.

Lake District, Howgills & Eden Valley

Scafell Pike

978 m

Scafell Pike is the highest ground in England, ringed by the deep valleys of Wasdale, Eskdale and Borrowdale. Its height is an advantage: a cloud sea that drowns lower fells can still leave the summit in clear air above an unbroken white layer.

Open the Scafell Pike forecast

Bannau Brycheiniog / Brecon Beacons

Pen y Fan

886 m

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.

Open the Pen y Fan forecast

Eryri / Snowdonia & North Wales

Cadair Idris

893 m

Cadair Idris rises between the Mawddach estuary at Dolgellau and the deep trench of Tal-y-llyn. Sea air and valley fog can fill both sides overnight, leaving Penygadair and the Tyrrau Mawr ridge standing above a two sided sea of cloud.

Open the Cadair Idris forecast

Peak District

Mam Tor

517 m

Track the signal around Edale, Hope Valley and Castleton, with the map centred on the ridge itself.

Open the Mam Tor forecast

Lake District

Helvellyn

950 m

Compare the dawn setup around Glenridding, Thirlmere and the valleys on both sides of the summit.

Open the Helvellyn forecast

Eryri / Snowdonia

Yr Wyddfa (Snowdon)

1,085 m

Compare the regional setup around Rhyd Ddu, Nant Gwynant and Llanberis beneath the summit.

Open the Yr Wyddfa forecast

Lochaber

Ben Nevis

1,345 m

Watch Glen Nevis, Fort William and Spean Bridge beneath the summit and its changeable Atlantic cloud.

Open the Ben Nevis forecast

Loch Lomond and the Trossachs

Ben Lomond

974 m

Compare low cloud around the loch and neighbouring glens with the summit and the air above it.

Open the Ben Lomond forecast

Isle of Skye

The Storr / Old Man of Storr

719 m

Use a close Trotternish map and distinguish the Storr summit from the lower Old Man pinnacle.

Open The Storr forecast

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