Bergeron–Findeisen Process

The Bergeron–Findeisen process explains how ice crystals grow at the expense of supercooled water droplets in cold clouds, leading to the formation of snow, sleet, or rain.

Process (step-by-step):

1. In mixed clouds (containing both ice crystals and supercooled water droplets), the saturation vapour pressure is lower over ice than over liquid water.
2. Water vapour moves from the droplets (where pressure is higher) to the ice crystals (where it is lower)
3. The ice crystals grow larger as vapour deposits on them, while the supercooled droplets shrink.
4. When the crystals become heavy enough, they fall.
   • If the air below the cloud is cold, they fall as snow or hail.
   • If the air below is warmer, they melt into raindrops before reaching the ground.

Where it occurs:

Common in mid-latitude and high-latitude regions, where clouds extend into sub-freezing temperatures.

Link to the water cycle:

The Bergeron–Findeisen process explains the formation of precipitation in cold clouds, particularly in frontal and orographic rainfall systems at higher latitudes.