1. PRECIPITATION Unit 2: Weather

2. WHAT IS PRECIPITATION?  When water falls to Earth, it is called precipitation. Rain, snow, sleet, and hail are all forms of precipitation.

3. HOW IS RAIN FORMED?  For rain to fall, the water drops in a cloud must reach a certain size. As the tiny droplets of water in a cloud bump into each other, they combine.  When the drops are heavy enough, they fall as rain.

4. HOW IS SNOW FORMED?  If the air is very cold, water vapor in a cloud may freeze into tiny ice crystals called snow. All snowflakes have six sides, or points.

5. HOW IS HAIL FORMED?  Hail may fall during a thunderstorm in the spring or summer. Hail begins as tiny pieces of ice in a thundercloud.  1 st - The piece of ice start to fall, but they are swept back up by a current of air.  2 nd - As the pieces fall again, they collect more water.  3 rd - This water freezes, making the hail larger.  This happens over and over again until its so heavy it falls to the ground.

6. DEW AND FROST  Sometimes you will find that blades of grass have drips of water on them even when it has not rained. This water is called dew.  Dew forms when there is a large amount of water vapor in the air.  1 st - At night, the air cools off.  2 nd - Cool air cannot hold as much moisture as warm air, so the water vapor forms into drops of dew.  3 rd - If the ground is very cold, the dew freezes and forms frost.