FogCast · Fog Formation Guide
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What Is a Temperature Inversion?

Inversions trap fog in valleys and create the sea-of-clouds effect photographers drive hours to shoot. LightCast FogCast factors inversion conditions into its fog probability and burn-off timing.

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Why cold air gets trapped

The Atmospheric Layer That Creates Valley Fog

Normally, air gets colder as you gain altitude. A temperature inversion reverses this: a layer of warm air sits above cooler surface air, acting as a lid. The cold air below can't rise and mix, so any moisture or fog it holds stays locked in place. For photographers, this is what creates the valley fog and sea-of-clouds conditions visible from ridges and peaks.

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Radiation Inversion: The Overnight Setup
Forms on clear, calm nights when the ground surface loses heat faster than the air above it. The surface cools, chilling the air immediately above it, while slightly warmer air sits just above that layer. This shallow inversion traps fog near the surface until solar heating disrupts it after sunrise.
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The Sea-of-Clouds Effect
When fog fills a valley up to the inversion lid and you shoot from elevation above it, the fog surface appears as a flat, luminous layer stretching to the horizon. Golden hour light from above catches the fog top in shades of orange and pink that the valley floor never sees. This is one of the most reliably spectacular conditions in landscape photography.
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Inversions Delay Burn-Off
A strong inversion prevents vertical mixing after sunrise, slowing the evaporation process that normally burns fog off by mid-morning. Fog under a deep inversion can persist until early afternoon. FogCast factors inversion strength into its burn-off timing estimate so you know whether the window will be short or extended.
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Where to Position Yourself
Inversion fog photography is a two-position game: in the fog for moody low-contrast shots before burn-off, or above the inversion looking down for the sea-of-clouds effect. The inversion lid height determines which elevation puts you above it. FogCast's fog depth estimate helps narrow down the right ridge height.
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How FogCast uses inversion data

Inversion Strength Affects Both Probability and Timing

A strong overnight inversion raises fog formation probability by concentrating cold, moist air at the surface. It also extends the fog duration by preventing mixing after sunrise. FogCast combines inversion conditions with dew point depression, overnight wind, recent precipitation, and terrain to give you a single probability score and estimated formation and burn-off window for your location.

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App Exclusive
FogCast is only available in the iOS app, alongside GoldCast, StarCast, DroneCast, CloudCast, and TriCast. GoldCast and StarCast send push alerts when golden hour or night sky conditions hit your threshold — one app covers your full photography forecast workflow.
Common Questions
What is a temperature inversion?
A layer of warm air sitting above cooler surface air, trapping the cold air below. Inversions prevent vertical mixing, which concentrates fog and moisture near the surface and delays burn-off. FogCast factors inversion conditions into its fog probability score — available in the LightCast iOS app.
What does a temperature inversion look like?
From elevation above the inversion: a flat, luminous fog layer filling the valley below with clear sky above. The sea-of-clouds effect. Golden hour light from above catches the fog surface in intense color that the valley floor never receives directly.
Does a temperature inversion mean more fog?
Generally yes. Inversions concentrate cold, moist air at the surface and prevent it from mixing upward, raising fog formation probability and extending the duration of any fog that does form. A strong inversion on a humid night after recent rain is one of the highest-probability fog setups FogCast flags.
How high do I need to be to shoot above an inversion?
It depends on the inversion lid height, which varies by night and location. Radiation inversions are typically shallow, from a few hundred to a few thousand feet above the valley floor. FogCast's fog depth estimate can help narrow the right elevation for sea-of-clouds positions.
What is LightCast FogCast?
FogCast scores fog formation probability using dew point depression, inversion conditions, humidity, overnight wind, sky coverage, terrain, and recent precipitation. Includes formation and burn-off timing. Exclusive to the LightCast iOS app. $2.99/month after a 7-day free trial.
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Know when inversions will trap fog in your valley.

Fog probability · Inversion conditions · Formation & burn-off timing
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