Collision-coalescence process of precipitation is applicable to

The collision-coalescence process is the primary mechanism for precipitation in 'warm clouds', which are defined as clouds that exist entirely at temperatures above 0°C. This process occurs when larger cloud droplets fall faster than smaller ones, colliding and merging (coalescing) with them to grow into raindrops [1]. Consequently, it is specifically applicable to clouds that do not extend beyond the freezing level, as they are composed entirely of liquid water droplets rather than ice crystals. In contrast, clouds that extend above the freezing level (cold clouds) primarily utilize the Bergeron-Findeisen process, where ice crystals grow at the expense of supercooled water droplets. While collision-coalescence can occur in the lower, warmer layers of tall clouds like cumulonimbus, the process itself is the defining characteristic of precipitation in clouds that remain below the freezing altitude.

Sources

1. [1] https://www.weather.gov/media/zhu/ZHU_Training_Page/clouds/cloud_precipitation/cloud_precipitation.pdf