What Is Weather

What Is Weather

Middle School

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Learning Objectives

• Describe the composition of Earth's atmosphere.

• Explain the different layers of the atmosphere and their key characteristics.

• Identify various types of severe weather phenomena.

• Differentiate between various types of storms like tornadoes, hurricanes, and blizzards.

Key Vocabulary

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Severe Weather

Unusual weather causing dangerous conditions that can damage property and threaten lives.

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Flood

An overflowing of a large amount of water beyond its normal confines, covering normally dry land.

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Drought

A prolonged period of unusually low rainfall, which leads to a severe shortage of water.

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Tornado

A violently rotating column of air that is in contact with the earth's surface and a cloud.

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Hurricane

A powerful storm with violent winds, which forms over warm tropical seas in the Caribbean.

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Atmosphere

The blanket of gases surrounding the Earth, held in place by the planet's gravitational pull.

Key Vocabulary

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Troposphere

The lowest layer of the atmosphere where almost all of our weather occurs on Earth.

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Stratosphere

The layer of Earth's atmosphere located right above the troposphere, extending to about 50 km high.

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Greenhouse Gas

A gas that absorbs infrared radiation, contributing to the greenhouse effect, like carbon dioxide.

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Air Pressure

The force exerted on a surface by the weight of the air due to gravity's pull.

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What Is Severe Weather?

• Severe weather is any weather that is out of the ordinary.

• It creates dangerous conditions that can damage property and harm people.

• This is a significant change from normal, predictable weather patterns.

• Examples include thunderstorms, tornadoes, hurricanes, and blizzards.

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Multiple Choice

What is the definition of severe weather?

• Weather that is out of the ordinary and creates dangerous conditions.

• Any type of weather that is predictable and normal.

• A normal weather pattern that happens every year.

• Weather that only includes thunderstorms and tornadoes.

Multiple Choice

What is the relationship between severe weather and normal weather patterns?

• It includes storms like hurricanes and blizzards.

• It is something that only happens in the summer.

• It represents a significant and potentially dangerous change from normal weather.

• It is always easy for meteorologists to predict.

Multiple Choice

A weather forecast for a desert region, which normally gets very little rain, predicts a storm with unusually heavy rainfall that is expected to cause flash floods. What conclusion can be drawn about this storm?

• The storm is a severe weather event because it is unusual and likely to cause harm.

• The storm is just a normal event that has been predicted.

• The storm will only damage property but will not be dangerous to people.

• This type of storm is a predictable and ordinary event for the area.

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Extreme Water Events: Floods and Droughts

Floods

• A flood happens when water overflows its banks, covering land that is normally dry.

• Floods are often caused by heavy rainfall, rapid snowmelt, or tsunamis.

• A flash flood is a sudden, fast-moving flow of water that occurs with little warning.

Droughts

• A drought is a long period with less-than-normal rainfall, causing water shortages.

• Droughts impact everything from stream flow to the levels of groundwater.

• They have serious consequences like wildfires, famine, and are disastrous for farming.

Multiple Choice

What happens during a flood?

• Water overflows its banks and covers land that is normally dry.

• A long period with less-than-normal rainfall occurs.

• Water freezes into large glaciers and ice sheets.

• Water evaporates quickly from the surface of the ocean.

Multiple Choice

What is the relationship between rainfall and these extreme water events?

• Heavy rainfall can cause floods, while a long period of little rainfall causes droughts.

• Rapid snowmelt causes droughts, while a lack of snowmelt causes floods.

• Tsunamis are a primary cause of droughts, not floods.

• Rainfall only impacts stream flow and has no effect on floods or droughts.

Multiple Choice

A farming region experiences a long period of below-normal rainfall, and its stream and groundwater levels are very low. Based on this information, what is another likely consequence for this region?

• An increased risk of wildfires.

• The sudden occurrence of a flash flood.

• The rapid melting of snow from nearby mountains.

• The overflowing of water from its usual banks.

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Thunderstorms and Hail

Thunderstorms

• A thunderstorm is a storm with lightning, thunder, and rapidly rising air currents.

• A storm becomes severe if it produces hail 1.9 cm or larger, or strong winds.

• Severe thunderstorms can also sometimes produce tornadoes.

Hail

• Hail is precipitation that is made of solid balls of ice called hailstones.

• Hailstones form inside tall and powerful thunderstorm clouds called cumulonimbus clouds.

• Strong winds carry water droplets upward into freezing temperatures, where they form hail.

Multiple Choice

What is a thunderstorm?

• A storm with lightning, thunder, and rapidly rising air currents

• A storm that only produces large balls of ice

• A type of cloud that is tall and powerful

• A strong wind that carries water droplets upward

Multiple Choice

What is the process that causes hail to form within a thunderstorm?

• Raindrops freeze as soon as they leave the cloud.

• Strong winds carry water droplets upward into freezing temperatures.

• Snowflakes melt and then refreeze together in the clouds.

• Tornadoes compress water vapor into solid ice.

Multiple Choice

A weather report indicates that a thunderstorm is producing hailstones that are 2.5 cm in diameter. Based on this information, what can be concluded about the storm?

• The storm is severe and has the potential to produce a tornado.

• The storm is a normal thunderstorm that is not dangerous.

• The hail will quickly melt before it reaches the ground.

• The storm will only produce rain and lightning from now on.

The Science of Lightning and Thunder

• Lightning is a powerful electric discharge produced by thunderstorms.

• Thunder is the explosive sound that accompanies a lightning strike.

• Lightning can be extremely destructive and is responsible for thousands of wildfires.

Multiple Choice

What is lightning?

• A powerful electric discharge produced by thunderstorms.

• The sound that accompanies an electric discharge.

• A type of fire that starts during a storm.

• A loud noise created by moving air.

Multiple Choice

What is the relationship between lightning and thunder?

• Thunder is the sound that results from a lightning strike.

• Lightning is the light that is created by the sound of thunder.

• Thunder and lightning are separate, unrelated events.

• Thunder is the cause of the electrical discharge in a storm.

Multiple Choice

Given that lightning is a powerful electric discharge and can cause wildfires, what can be concluded?

• Lightning must transfer a large amount of energy to the ground.

• All thunderstorms are capable of causing wildfires.

• Thunder is the most destructive part of a thunderstorm.

• Wildfires can only be started by lightning strikes.

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Powerful Rotating Storms: Tornadoes & Hurricanes

Tornadoes

• A tornado is a fast-spinning column of air that connects a thunderstorm to the ground.

• Its powerful winds can reach speeds of over 417 kilometers per hour, picking up dust and debris.

• The visible funnel cloud gets its dark color from the dust and debris it picks up.

Hurricanes

• A hurricane is a large storm system that forms over warm oceans with a calm "eye" at its center.

• They bring destructive winds, heavy rains, and severe flooding to coastal areas when they make landfall.

• Depending on the location, they can also be called typhoons or tropical cyclones.

Multiple Choice

What is the primary difference between a tornado and a hurricane as described in the text?

• A tornado is a spinning column of air from a thunderstorm, while a hurricane is a large storm system from the ocean.

• A tornado has a calm 'eye' at its center, while a hurricane is a single column of air.

• A tornado brings heavy rain and flooding, while a hurricane picks up dust and debris.

• A tornado is also called a typhoon, while a hurricane is also called a cyclone.

Multiple Choice

What is the relationship between a tornado's powerful winds and its visible appearance?

• The powerful winds pick up dust and debris, which makes the tornado's funnel cloud look dark.

• The dark color of the funnel cloud causes the powerful winds to spin faster.

• The friction from the powerful winds burns the air, making it look dark.

• The funnel cloud is a shadow cast by the thunderstorm that creates the winds.

Multiple Choice

A large storm, sometimes called a typhoon in its region, is moving from the ocean toward a coastal city. What should the people in that city primarily prepare for?

• A fast-spinning funnel cloud that picks up dust and debris.

• The storm becoming stronger as it moves over the city.

• Destructive winds, heavy rains, and potential flooding.

• The storm being renamed a tornado once it makes landfall.

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Winter Storms and High Winds

Blizzards

• Blizzards are intense winter storms with low temperatures, strong winds, and heavy blowing snow.

• The strong winds must be over 51 km per hour, making it very difficult to see.

• A severe blizzard has winds over 72 km/h and frigid temperatures of -12°C or lower.

High Winds

• Straight-line winds are very fast winds that do not have any kind of rotation.

• Microbursts are powerful, small-scale winds that travel downwards from a thunderstorm.

• Dust devils are small, rotating winds that form on hot days and are seen by the dust they carry.

Multiple Choice

Which set of conditions best describes a blizzard?

• Low temperatures, strong winds, and blowing snow

• Hot temperatures, rotating winds, and dust

• Heavy rain, mild winds, and lightning

• Downward winds, no rotation, and thunderstorms

Multiple Choice

How are microbursts distinguished from other types of high winds?

• Microbursts are powerful winds that travel downwards from a thunderstorm.

• Microbursts are small, rotating winds that form on hot days.

• Microbursts are very fast winds that do not have any kind of rotation.

• Microbursts are intense winter storms with very low temperatures.

Multiple Choice

A winter storm has winds of 75 km/h and a temperature of -10°C. How would this storm be classified?

• A blizzard, but not a severe blizzard because the temperature is not low enough.

• A severe blizzard because the winds are over 72 km/h.

• A microburst because the winds are powerful.

• A straight-line wind storm because it is not rotating.

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Composition of the Atmosphere

Permanent Gases

• These gases are found in constant amounts in the atmosphere and are very stable.

• Nitrogen (N₂) is the most common gas, making up about 78% of the atmosphere.

• Oxygen (O₂), essential for all living things, makes up about 21% of the atmosphere.

Variable Gases

• The amounts of these gases change based on environmental activities and location.

• This group includes water vapor, carbon dioxide (CO₂), methane, and ozone.

• These are also called greenhouse gases because they trap heat, warming the Earth.

Multiple Choice

What is the main difference between permanent and variable gases in the atmosphere?

• Their amounts are either constant or change over time.

• One group is essential for life, while the other is not.

• Permanent gases are much warmer than variable gases.

• One group is made of solids, while the other is made of gases.

Multiple Choice

What is the primary role of variable gases like carbon dioxide and methane in the atmosphere?

• They combine to form the most common gas in the atmosphere.

• They are essential for all living things to breathe.

• They remain in constant and stable amounts everywhere on Earth.

• They trap heat, which helps to warm the Earth.

Multiple Choice

If a large number of factories are built in an area, releasing significant amounts of carbon dioxide (CO₂), what is the most likely impact on the atmosphere's composition in that location?

• The percentage of variable gases would increase, likely causing an increase in trapped heat.

• The amount of permanent gases like nitrogen and oxygen would increase.

• The overall composition of the atmosphere would become more stable.

• The percentage of oxygen would increase, making it easier for living things to breathe.

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Layers of the Atmosphere

• The atmosphere is divided into layers based on its temperature changes.

• The troposphere is the lowest layer, where weather happens.

• The stratosphere contains the ozone layer and the mesosphere burns up meteors.

• The thermosphere has auroras and the exosphere fades into space.

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Multiple Choice

What is the main principle used to divide the atmosphere into layers?

• The types of gases present in each layer.

• The distance of the layer from the sun.

• Changes in temperature as altitude increases.

• The amount of weather that occurs in each layer.

Multiple Choice

How can the functions of the stratosphere and the troposphere be compared?

• The stratosphere contains the ozone layer, while the troposphere is where weather happens.

• The troposphere burns up meteors, while the thermosphere contains the ozone layer.

• The mesosphere is the lowest layer, while the exosphere is where auroras occur.

• The thermosphere is where weather happens, while the stratosphere fades into space.

Multiple Choice

A spacecraft returning to Earth from deep space would pass through the atmospheric layers in sequence. Which option correctly orders the phenomena the spacecraft would encounter as it descends?

• Weather clouds, then auroras, then burning meteors.

• Auroras, then burning meteors, then weather clouds.

• Burning meteors, then weather clouds, then auroras.

• Ozone layer, then auroras, then burning meteors.

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Common Misconceptions

Misconception	Correction
Lightning never strikes the same place twice.	Lightning often strikes the same place multiple times, especially tall structures.
The atmosphere is made mostly of oxygen.	The atmosphere is composed of 78% nitrogen and only about 21% oxygen.
Opening windows before a tornado will equalize pressure and save a house.	This is a dangerous myth and can increase the destructive forces of the tornado.
A car is safe from a tornado because it's heavy.	Tornadoes can easily pick up and throw cars.

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Summary

• Earth's atmosphere is mostly nitrogen and oxygen, with variable amounts of other gases.

• The atmosphere has four main layers: the Troposphere, Stratosphere, Mesosphere, and Thermosphere.

• Hurricanes form over warm oceans, while tornadoes form over land from thunderstorms.

• Lightning is an electrical discharge, and thunder is the sound it creates.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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