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8.5: Precipitation

Difficulty Level: Basic Created by: CK-12
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Want to stay dry? Don't go to these places!

The wettest locations in the world are in Mawsynram and Cherrapunji in India. Monsoon rains result in more than 460" of rain annually. The wettest place in the United States with 404" on average is on Maui (Big Bog). The wettest place in the continental United States is Langlois, Oregon with a mere 122" per year.

Precipitation

Clouds are needed for precipitation. Precipitation is water that falls from the sky. This may fall as liquid water, mostly as rain. It may fall as frozen water, such as snow.

Why Precipitation Falls

Millions of water molecules in a cloud must condense to make a single raindrop or snowflake. The drop or flake falls when it becomes too heavy for updrafts to keep it aloft. As a drop or flake falls, it may collect more water and get larger.

Types of Precipitation

Why does it snow instead of rain? Air temperature determines which type of precipitation falls. Rain falls if the air temperature is above freezing (0° C or 32° F). Frozen precipitation falls if the air or ground is below freezing. Frozen precipitation may fall as snow, sleet, or freezing rain. You can see how the different types form in Figure below.

Frozen precipitation may fall as snow, sleet, or freezing rain.

Vocabulary

  • freezing rain: Rain that falls as liquid but freezes on the surface it falls on.
  • hail: Balls of ice formed as water freezes and in layers in the strong updrafts of thunderstorms.
  • precipitation: Water that falls from the sky as rain, snow, sleet, or hail.
  • rain: Liquid water that falls from the atmosphere.
  • sleet: Raindrops that freeze to ice before striking the ground.
  • snow: Frozen precipitation in patterns.

Summary

  • Precipitation falls when it gets too heavy to stay in a cloud.
  • Rain droplets caught up in air currents within a cloud get larger by the addition of condensed droplets until they are too heavy and they fall.
  • If the ground is very cold, rain can freeze to become sleet or glaze.

Practice

Use this resource to answer the questions that follow.

http://www.youtube.com/watch?v=kFFHo4T-g4E&feature=player_embedded

1. What is precipitation?

2. What is the most common form of precipitation?

3. What is hail?

4. What is sleet?

5. What is snow?

Review

1. Describe how raindrops form.

2. Why does hail only come from cumulonimbus clouds?

3. How does sleet form?

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    Vocabulary

    freezing rain

    Rain that falls as liquid but freezes on the surface it falls on.

    precipitation

    Water that falls from the sky as rain, snow, sleet, or hail.

    rain

    Liquid water that falls from the atmosphere.

    sleet

    Raindrops that freeze to ice before striking the ground.

    snow

    Frozen precipitation in patterns.

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    Difficulty Level:
    Basic
    Grades:
    6 , 7
    Date Created:
    Jan 04, 2013
    Last Modified:
    Aug 29, 2016
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