Science With Sabrina: Why It Rains

In fall, many cold fronts, along with rain, move through the area. It has to do with cloud physics! Meteorologist Sabrina Bates explains why it rains on this week’s Science With Sabrina.


I'm showing how rain forms by using a tank filled with water. All of this water represents the air that's all around us.

Water vapor begins to rise and form a cloud. That's the shaving cream. Now, I drop food coloring onto it. These are water droplets that are added to the cloud. These tiny droplets begin to stick together. The droplets grow and eventually get too heavy to stay suspended in the cloud. When the cloud can't hold anymore water, rain falls.


One process allows precipitation to form under supercooled conditions. This is called the Bergeron process. But, there's a process that allows for cloud droplets to grow called collision and coalescence. Let's break that down.

Water droplets will continue to move around. When the droplets bump into each other, it's called a collision. If these droplets stick together, that's called coalescence. These processes increase the size of the raindrops. And, we learned during the experiment that once those raindrops become too big and heavy, they fall to the ground.

Segment Sponsored By: Sylvan Learning


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