(WC) Precipitation Lesson

Precipitation

Through the water cycle, water is evaporated into the air and becomes water vapor. This water will eventually find its way back to the Earth's surface as precipitation. Precipitation includes any form of water that falls from clouds and reaches Earth's surface.

Types of Precipitation

The type of precipitation a region gets depends largely on the temperature and air density in that region.

Common types of precipitation include:

• rain
• sleet
• freezing rain
• hail
• snow

Rain

Rain is the most common type of precipitation. For a water droplet to be considered rain it must measure at least 0.5 millimeters in diameter. Droplets of water smaller than 0.5 millimeters are referred to as mist or drizzle. Nimbostratus clouds are more likely to produce mist or drizzle.

Sleet

The freezing point of water is 0°C. When rain falls through a freezing temperature layer the droplets of water will form ice particles in the raindrop. Sleet are ice particles that are smaller than 5 millimeters in diameter.

Freezing Rain

Sometimes rain will fall through cold air but will freeze once it hits a very cold surface. This phenomenon is known as freezing rain since it is rain that freezes. Freezing rain can be extremely dangerous because surfaces will build up with layers of ice. Ice is dense and heavy making tree limbs and power lines to weigh down and sometimes to break. Freezing rain and sleet can both make driving treacherous because roads, streets, and even sidewalks become slick and slippery.

Hail

When precipitation occurs as round pellets of ice, measuring larger than 5 millimeters in diameter they are called hailstones. Cululonimbus clouds are the only types of clouds that produce hailstones during thunderstorms. Hail forms in storm clouds. Tiny water droplets are circled through the clouds through updrafts and downdrafts. Each cycle adds a new layer of ice to the droplet. Here, hail-producing storm clouds cross through South Dakota. In a record-setting July 2010 South Dakota hail storm, hail as large as 20 centimeters (8 inches) in diameter smashed through car windshields and left craters in the ground.

Snow

Water vapor in a cloud can be converted into ice crystals or better known as snowflakes. Snowflakes have an endless number of different shapes and patterns; however, all snowflakes will have six sides or branches.

Measuring Precipitation

A rain gauge is used to measure rainfall. A rain gauge is a can or tube with one open side that will collect rainfall. Snow is measured with a ruler or by measuring collected and melted snow.

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