Download Ch. 3 Sec. 2 Notes

Ch. 3 Sec. 2 Notes
Storms
*A storm is a violent disturbance in the atmosphere
-Storms involve sudden changes in air pressure, which in turn cause rapid air
movements
Thunderstorms
How Thunderstorms Form
*A thunderstorm is a small storm often accompanied by heavy precipitation and
frequent thunder and lightening
*Thunderstorms form in large cumulonimbus clouds, also known as thunderheads
-Cumulonimbus clouds form on hot, humid afternoons
-These clouds can also form when a cold front pushes the warm
Lightening and Thunder
*During a thunderstorm, areas of positive and negative electrical charges build up
in the storm clouds
*Lightning is a sudden spark, or electrical discharge, as these charges jump
between parts of a cloud, or between the cloud and ground
*How does thunder form?
1. Lightning heats up the sky to 30,000 C, much hotter than the sun's
surface
2. The rapidly heated air expands suddenly and explosively
3. Thunder is the sound of the explosion
4. Because light travels faster than sound, you see lightning
Thunderstorm Damage
*The heavy rains that come with thunderstorms can cause flash floods
*Lightning can strike buildings, trees and spark fires
*Lightning can strike people or animals, causing unconsciousness, severe burns, or
heart failure
Floods
*Floods occur when so much water pours into a stream or river that its banks
overflow, covering the surrounding land
Thunderstorm Safety
*Stay indoors during a thunderstorm
*Avoid places where lightning may strike
Tornadoes
*A tornado is a rapidly whirling, funnel-shaped cloud that reaches down from a
storm cloud to touch Earth's surface
*Wind speeds can reach up to 500 km/h
How Tornadoes Form
*Tornadoes most commonly develop in thick cumulonimbus clouds
*Form in spring and early summer when the ground is warm and humid
*Form when a maritime tropical air mass meets a continental polar air mass
Tornado Alley
*Occur more often in the US than any other country in world
-800 tornadoes occur each year
*Weather patterns in the Great Plains results in a "tornado alley"
Tornado Damage
*Damage comes from both strong winds and flying debris
*Tornados are so dangerous because they are so unpredictable
*Tornadoes are classified by how fast their wind speed is and how much damage it
causes
-Use the Fujita scale to measure
-F0 is a minor tornado, F5 is the most severe
Tornado Safety
*The safest place to be during a tornado is in a storm shelter or the basement of a
well-built building
*Stay away from windows and doors
*If you are outside, lay flat down in a ditch
Hurricanes
*A hurricane is a tropical cyclone that has winds of 119 km/h or higher
*A typical hurricane is about 600 km wide
How Hurricanes Form
*Hurricanes affect the US in August, September, or October
*Form in the Atlantic Ocean
*A hurricane begins over warm ocean water as a low-pressure area, or tropical
disturbance
*If a tropical disturbance grows in size and strength, it becomes a tropical storm,
which may turn into a hurricane
*A hurricane draws its attention from the warm, humid air at the ocean's surface
*Inside the storm are strong winds and heavy rain
*Hurricane winds are strongest in a narrow band around the center of the storm
*At the center is a ring of clouds, called the eyewall that holds the "eye" of the
storm
*When the eye hits, the sky becomes very calm, but when the storm keeps moving,
the other side of the storm hits and the wind is blowing in the opposite direction
How Hurricanes Move
*Hurricanes can last up to a week or longer
*Once the hurricane hits land, it can no longer gain strength from warm water, so
it will weaken, but rain for several days
Hurricane Damage
*Hurricanes bring high waves, severe flooding, and strong winds, which can all
cause great damage
*A storm surge forms when a hurricane raises the level of the ocean and then
crashes onto the shore destroying everything in its path
Hurricane Safety
*Scientists are very good at detecting when a hurricane is coming and can warn
people with enough timing to get out
*A "hurricane watch" means a hurricane can hit in 36 hours
*A "hurricane warning" means that it will hit land in less than 24 hours
Winter Storms
*All year round, most precipitation begins in clouds as snow
*If the air is colder than 0 C all the way to the ground, the precipitation falls as
snow
Lake-Effect Snow
*Cold, dry air mass travels over a lake and picks up its water vapor and drops it as
snow once it passes to land
Snowstorm Safety
*Find shelter from the snow and wind
*Do not drive
*If stuck in car, keep engine running