The formation of clouds and precipitation can be simplified into a simple recipe: water and dust.

Clouds are composed primarily of water in its liquid and solid state.

Thus, we begin our recipe by collecting sufficient water vapour - that we will soon transform into the liquid or solid states. The water vapor content of the atmosphere varies from near zero to about 5 percent, depending on the moisture on the surface beneath and the air temperature.

Next, we need some dust (Micrometric solid particles). Without "dirty air" there would likely be no clouds at all or only high altitude ice clouds. Even the "cleanest" air found on Earth contains about 1000 dust particles per cubic meter of air. Dust is needed for condensation nuclei, sites on which water vapor may condense or deposit as a liquid or solid. Without a nuclei for water to condense onto, air has been known to become “supersaturated” with water in lab conditions, up to 400% of the usual maximum humidity.

With proper quantities of water vapor and dust in an air parcel, the next step is for the air parcel mass to be cooled to a temperature at which cloud droplets or ice crystals can form (dew point).