Severe Weather 1

Hurricanes, Thunderstorms, and Tornadoes 2

Ingredients for a storm… Heat From the Sun Differences in Air Pressure Water 3

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What is a hurricane? A hurricane is a large, swirling, low- pressure system that forms over the warm Atlantic Ocean. 5

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Hurricanes form over warm ocean water. Near the equator, warm ocean water provides the energy that can turn a low pressure center into a violent storm. As water evaporates from the ocean, energy moves from the ocean water to the air. This energy makes warm air rise faster. Tall clouds and strong winds develop. 8

As winds blow across the water from different directions into the low, the Coriolis Effect bends their path into a spiral. The winds blow faster and faster, around the low, which becomes the center of a storm system. 9

Parts of a Hurricane 10

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Parts of a Hurricane Eye - The calm, center of the hurricane. Eyewall - The wall of dense thunderclouds surrounding the eye. The strongest winds of the hurricane are in the eyewall. Spiral Rainbands - A series of long, spiraling bands of rain clouds in a hurricane. 12

What things make hurricanes loose strength? 1. Crumple a piece of paper, then flatten it out. Crumple and flatten it out again. 2. Spin the top on the flattened paper. 3. Spin the top on a smooth surface. Count the seconds until it stops spinning. What do you think? How does the texture of the surface affect the rate at which the top looses energy? 13

Why do hurricanes seem to die over land? As long as a hurricane is over water, the warm, moist air rises and provides energy for the storm. When a hurricane reaches land, however, its supply of energy disappears and the storm loses power. 14

Create a Model of a Hurricane! Using glue, blue construction paper, and cotton balls, create a model of a hurricane, labeling and explaining each part. You may use your graphic organizer for assistance! 15

Tornadoes Tornadoes form from severe thunderstorms. They are very destructive because they have a high energy density. They also don't last very long. This makes it hard to learn about them. Since scientists don't know much about tornadoes, it's also hard to forecast them 16

Tornadoes The fastest recorded wind speed is 230 miles per hour and occurred in New Hampshire in 1934. Although, winds can get faster in tornadoes. The windiest place in the world is in Antarctica. 17

In severe thunderstorms, wind at different heights blows in different directions and at different speeds. This difference in wind speed and direction, called wind shear, creates a rotating column parallel to the ground. 18

A thunderstorm’s updraft can tilt the rotating column upward into the thunderstorm creating a funnel cloud. If the funnel comes into contact with Earth’s surface, it is called a tornado. 19

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Tornado Alley This map shows where most tornadoes form in the United States. The red area is known as "Tornado Alley". Warm moist air from the Gulf of Mexico collides with Cold dry air. 21

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Thunderstorms It is late afternoon. The white puffy clouds that have been growing all day are replaced by a greenish sky. A distant rumble is heard...then another. It starts to rain. A flash of light streaks the sky, followed by a huge BOOM. Welcome to a thunderstorm. 23

Thunderstorms Thunderstorms are small, intense weather systems that produce strong winds, heavy rain, lightning, and thunder. 25

When do thunderstorms occur? Thunderstorms form from warm moist air and along cold fronts. 26

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How are thunderstorms created? There are three ingredients for thunderstorms to form: 1. The air near the earth’s surface must be warm and moist. It rises or moves upward, which is called an updraft. 2. The atmosphere must be unstable- the surrounding air is colder than the rising air mass. As the warm air mass rises, it cools and turns into water vapor, condenses and forms CUMULONIMBUS Clouds. 28

Vertical Air Movement 3. As the cloud continues to build, ice particles form near the top of the cloud. As they get large-they form H-A-I-L. As the ice particles or H-A-I- L falls, cold air moves down with it, causing a downdraft. 29

Let’s Investigate! How do updrafts form??? Draw and describe what happens. In what ways is this demonstration of water similar to warm air in a thunderstorm? Challenge: How could you create a downdraft in this experiment? 30

Three Stages of a Thunderstorm Create a Foldable on Stages of a Thunderstorm. Turn to page 589 in the text book. Draw, Label, and Explain the stages of a thunderstorm. 31

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