Chapter 9: Weather Factors Section 5: Precipitation clouds

Precipitation Precipitation – any form of water that falls from clouds and reaches Earth’s surface

Precipitation Not all clouds produce precipitation. For precipitation to occur, cloud droplets or ice crystals must grow heavy enough to fall through the air.

Types of Precipitation Rain Sleet Freezing rain Snow Hail

Types of Precipitation Rain – most common kind of precipitation ◦ At least 0.5 millimeters ◦ Smaller drops of water are called drizzle. Sleet – solid particles of ice ◦ Smaller than 5 millimeters ◦ As raindrops fall they pass through a layer of air below 0 ºC and freeze into these ice particles.

Types of Precipitation Freezing rain – raindrops that freeze when they touch a cold surface. ◦ Does not freeze in the air ◦ A thick layer of ice builds up on every surface

Types of Precipitation Snow – Water vapor in a cloud that is converted directly into ice crystals ◦ Snowflakes have an endless number of different shapes and patterns all with six sides or branches

Types of Precipitation Hail – round pellets of ice larger than 5 millimeters in diameter Only forms in cumulonimbus clouds during thunderstorms

Modifying Precipitation Cloud Seeding – tiny crystals of silver iodide and dry ice are sprinkled into the clouds from airplanes.

Measuring Precipitation Snowfall Measurement ◦ A measuring stick ◦ Melting collected snow  Measuring the depth  10 centimeters of snow contains about the same amount of water as 1 centimeter of rain

Measuring Precipitation Rain Measurement ◦ Rain Gauge – an open-ended can or tube that collects rainfall ◦ Measured by dipping a ruler into the water or reading a marked scale