Answer to Question 1
The Bergeron process is the formation of precipitation by the growth of ice crystals in clouds. Thus, temperatures must be cold enough to keep ice crystals frozen.
Answer to Question 2
The collisioncoalescenc e process forms with warm clouds, typically in the tropics, where clouds composed entirely of liquid droplets contain some droplets at least 20 micrometers in size. As these large droplets fall through the air, they collide with smaller droplets. After many of these collisions, the droplets may grow large enough to fall to the surface without evaporating.