Clouds form when warm air rises from Earth's surface toward the higher and colder part of the atmosphere.

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​Cloud Formation

​​An Energy Source

​​Moisture

Unstable Air

Conditions Needed for a Severe Storm

• Can come from temperature differences between two air masses, or

• From heat absorbed by Earth's surface that warms the air above it.

*** The warmer the ground or ocean water below a developing storm, the more energy it can transfer to the storm as it grows.

Energy Source

• Energy from the sun transfers to water on the surface and causes evaporation. The water vapor holds onto that energy until it condenses into a cloud and the energy is then released in the form of heat, which fuels the storm's growth.

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​Moisture

• Occurs when air surrounding the storm is significantly colder than air at lower levels.

• The greater the temperature difference between a storm cloud and its surroundings, the faster, higher, and more intense it will grow.

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​Unstable Air

​When multiple thunderstorms form near each other in an area over warm ocean water, they can combine to form the start of a hurricane - Earth's most powerful and devastating type of storm.

​Hurricanes are also known as:

• typhoons

• cyclones

​​Many Names

​are at least 74 miles per hour.

​​Wind speeds

​tropical depression, which is a line of rain showers and weak thunderstorms that circle around an area of low air pressure.

​​Begin as a

​must be at least 79 degrees Fahrenheit.

​​Ocean water

• Once the winds reach 38 mph, the tropical depression becomes a tropical storm.

• When winds reach 74 mph, it's officially a hurricane.

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​Formation of a Hurricane

• As the hurricane reaches land, it loses the warm water that fuels it and weakens.

• BUT, dangerous winds can still cause damage and storm surges (when the strong storm pushes ocean water ashore) can flood coastal areas with more than 20 feet of water!

​​Temperature

​​Cloud Formations

​​Air Circulation

​Meteorologists analyze changes in...

​...when predicting the path of a hurricane.

• also known as a twister

• violently spinning, funnel-shaped columns of air that stretch from the dark thunderclouds they form in all the way to the ground

• wind can top 250 mph!

• extreme wind gusts can cause major damage

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​What exactly is a tornado?

• when cold, dry air is pushed over warm, humid air

• When that warm air rises through the colder air, it causes an updraft, or a change in wind direction.

• If these winds vary greatly in speed or direction, rotation will begin.

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​How do tornadoes develop?

• As the rotating air pulls in more warm air from the thunderstorm, it spins faster and a funnel cloud forms.

• As it gains strength, the funnel becomes longer and more visible (as dirt and debris are caught in it).

• It's more dangerous when it touches the ground.

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​How does it form from this rotation?

• BUT some can rage for over an hour!

• They usually weaken when they move over colder ground or when the clouds above it start to break apart.

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​The average tornado only lasts about 10 minutes.