Fog happens when air near the ground cools enough that its water vapor condenses into tiny suspended droplets, essentially making a low cloud you can walk through. This usually needs moist air, cooling to the dew point, and light winds so the droplets can hang in place instead of blowing away.

What fog actually is

Fog is basically a cloud that forms at ground level, made of countless microscopic liquid water droplets or ice crystals suspended in the air. Because those droplets scatter light, they sharply reduce visibility and give that milky, “everything looks faded” appearance.

The core recipe: moisture + cooling

Fog forms when:

  • The air is very moist, close to 100% relative humidity.
  • The air temperature drops to (or very close to) the dew point, the temperature at which water vapor starts condensing.
  • Winds are light, so the cooled, saturated air stays in place instead of mixing away.

When the air cools below what it can “hold” as invisible vapor, excess vapor turns into droplets, and that’s the fog you see.

Main types of fog (quick tour)

Different weather setups can produce fog in slightly different ways:

  • Radiation fog: Forms on clear, calm nights when the ground loses heat to space, cooling the air just above it until condensation occurs; common in valleys and autumn/winter mornings.
  • Advection fog: Forms when warm, moist air glides over a colder surface (like cool ocean or land), gets chilled, and its moisture condenses; common along coasts.
  • Evaporation (steam) fog: Occurs when cold air passes over warmer water or moist ground, picking up moisture that then condenses in the chilly air; seen over lakes and ponds.

All of these follow the same basic rule: saturate and cool the air near the ground until droplets form.

Why fog often appears in mornings (and after rain)

  • Nights and early mornings are when the ground cools most, pulling down air temperature toward the dew point and triggering condensation.
  • After rain, there is lots of extra moisture in the air and on surfaces, so it takes only a bit of cooling for fog to develop.

As the sun rises and warms the ground, the air warms, relative humidity drops, and the droplets evaporate, so fog “burns off.”

When fog disappears

Fog will thin or vanish when:

  • The air warms above the dew point, causing droplets to evaporate.
  • Drier air mixes in, lowering humidity below saturation.
  • Stronger wind stirs the air, breaking up the shallow cool, moist layer near the surface.

In short, whenever you see fog, you’re looking at air that’s both very moist and just cool enough that its invisible vapor has turned into a floating cloud at your feet.

Information gathered from public forums or data available on the internet and portrayed here.