1. Precipitation
Chapter 4 lesson 3

2. Objective 1. Identify the common types of precipitation.
2. Describe floods and droughts and their effects.
Standards
MS-ESS3.B.1 Mapping the history of natural hazards in a region, combined with an understanding of related geologic forces can help forecast the locations and likelihoods of future events.

3. Cloud Seeding My Planet Diary
Is that a space weapon you see in this photo? Not at all.
This device is being prepared to launch tiny crystals of silver iodide into the air to make rain.
Clouds often contain water droplets that have cooled below 0ºC.
But the droplets do not freeze unless they can condense onto solid particles.
When the silver iodide crystals reach the clouds, the droplets can condense onto them.
Once that happens, the droplets can fall as rain.
Some scientists think that cloud seeding can increase rainfall by 10 percent.
Others think that this is unlikely. In the United States, several western states are trying cloud seeding.
Dry states, such as Wyoming and Utah, need as much rainfall as they can get.
Why would scientists want to find a way to make it rain?
Name a situation when you would want it to rain.

4. How does Precipitation Form?
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5. What Are the Common Types of Precipitation? Key Concept Summary
Any form of water that falls from clouds and reaches Earth’s surface is precipitation.
Common types of precipitation include rain, sleet, freezing rain, snow, and hail. 
Rain  The most common type of precipitation is rain. Drops of water are called rain if they are at least 0.5 millimeters in diameter. Smaller drops of water are called drizzle, and even smaller ones are called mist.
Measuring Rain  An open-ended can or tube that collects rainfall is called a rain gauge. 

6. What Are the Common Types of Precipitation?
Freezing Precipitation  There are four types of freezing precipitation: freezing rain, snow, sleet, and hail. 
Freezing rain is rain that freezes when it hits a cold surface.
When clouds are colder, water vapor can convert directly into ice crystals, forming snow.
When raindrops fall through a layer of air colder than 0°C, they can freeze into ice particles.
Ice particles smaller than 5 millimeters in diameter are called sleet.
Round pellets of ice larger than 5 mm in diameter are called hailstones. Hail forms only inside cumulonimbus clouds during thunderstorms.
It forms when strong updrafts repeatedly carry ice pellets through cold regions of a cloud, adding another layer of ice each time.

8. What Are the Causes and Effects of Floods and Droughts
What Are the Causes and Effects of Floods and Droughts? Key Concept Summary
Floods A flood is an overflowing of water in a normally dry area.
Small or large, many floods occur when the volume of water in a river increases so much that the river overflows its channel.
Over a brief time period, heavy rains or melting snow can cause a river to overflow, uprooting trees and even destroying bridges and buildings.
People try to control floods by building dams across rivers and levees.

9. What Are the Causes and Effects of Floods and Droughts
What Are the Causes and Effects of Floods and Droughts? Key Concept Summary
Droughts A long period of scarce rainfall or dry weather is known as a drought.
Because it reduces the supplies of groundwater and surface water, a drought can cause a shortage of water for homes and businesses. 
Droughts are usually caused by dry weather systems that remain in one place for weeks or months at a time.
Long-term droughts can cause crop failure and even famine.
People can prepare for droughts by conserving water when dry conditions first occur.
Farmers can grow drought-resistant plants that have been bred to withstand dry conditions.