http://www.youtube.com/watch?v=jM8h60S1GsM Severe Weather

Severe Weather Severe weather is weather that can cause property damage and sometimes death Examples of severe weather are: Thunderstorms Tornadoes Hurricanes

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

Thunderstorms Thunderstorms can occur at cold fronts. There are only two atmospheric conditions required to produce thunderstorms: Warm, moist air near the Earth’s surface An unstable atmosphere.

Thunderstorm Development The atmosphere is unstable when the surrounding air is colder than the rising air mass. The air mass will continue to rise as long as the surrounding air is colder than the air mass. When the warm rising air reaches its dew point, the water vapor condenses and forms cumulus clouds

Thunderstorm development If the atmosphere is extremely unstable, the warm air will continue to rise, which will cause the cloud to grow into a dark, cumulonimbus cloud.

Lightning Thunderstorms can be active electrically. http://www.youtube.com/watch?v=G7GbOFlFODE Lightning is an electric discharge between a positively charged area and a negatively charged area. Lightning can happen between two clouds, the Earth and a cloud, or even between two parts of the same cloud.

Lightning When lightning strikes, energy is released. This energy is transferred to the air, and the heated air expands rapidly, sending out sound waves. Thunder is the sound that results.

Severe Thunderstorms Severe thunderstorms can produce one or more of the following conditions: High winds Hail Flash floods Tornadoes

Tornadoes Tornadoes only happen in about 1% of all thunderstorms. A tornado is a rapidly spinning, column of air that has high wind speeds and low pressure. http://www.youtube.com/watch?v=S-UPAcKNvII Tornadoes start as a funnel cloud that pokes through the bottom of a cumulonimbus cloud, when/if the funnel cloud touches the ground, it becomes a tornado

Tornadoes About 75% of all tornadoes on Earth happen in the US Most occur in the spring or early summer Cold, dry air from Canada meets up with warm, moist air from the tropics Wind speeds average 120 mph

Hurricanes Hurricanes are large, rotating, tropical weather systems with wind speeds of at least 75 mph. Hurricanes are the most powerful storms on Earth. http://www.youtube.com/watch?v=4f45jA5UxB0 Hurricanes develop near the equator between 5* and 20* North and South latitudes over warm, tropical oceans

Hurricane Formation A hurricane begins as a group of thunderstorms that move over tropical waters. Winds moving in different directions meet and cause the storm to spin.

Hurricane Energy A hurricane gets its energy from the condensation of water vapor. The warm water of the ocean provides fuel for the hurricane. Moisture is added to the warm air by evaporation from the ocean. As the warm, moist air rises, the water vapor cools and condenses and releases huge amounts of energy. As long as the hurricane has warm water as fuel, it will continue to grow Once it passes over land or colder waters, it will begin to die as it loses its source of energy