Presentation on theme: "Severe Weather. Thunderstorms Small intense systems that can produce strong winds, rain, lightning and thunder. Need 2 conditions –Air near surface needs."— Presentation transcript:
Thunderstorms Small intense systems that can produce strong winds, rain, lightning and thunder. Need 2 conditions –Air near surface needs to be warm and moist –The atmosphere must be unstable
Becoming unstable… The surrounding air is colder than the rising air mass –This makes that rising air CONTINUE rising The thunderstorm occurs when the air is rising rapidly –Forms cumulonimbus cloud
Lightning! Electrical charges build up near the tops and bottoms of clouds heading from positive to negative to positive (opposites attract) Flash of light occurs when a charge sparks The flash heats the air to about the temperature of the surface of the sun ENERGY IS RELEASED
Effects Thunderstorms can have positive or negative effects Positive – rain can provide water for crops and restore lakes and streams Negative –Flash floods –Winds –Hail –Lightning
Funnel Cloud v. Tornado Wind traveling in 2 different directions causes it to start spinning The updrafts of air push the spinning column down, sometimes to the ground It is called a tornado once it hits the ground Funnel cloud Tornado
Tornadoes Cumulonimbus clouds can sometimes form tornadoes Only 1 percent of thunderstorms form tornadoes
Formation About 75 percent of tornadoes happen in the United States. –Warm humid air comes up from the Gulf of Mexico and meets cold dry air from Canada in the plains.
Effects Winds usually average around 95mph Most are small and last only a few minutes Larger ones are less common (~20%) are strong enough to knock over trees, lift cars or take roofs off houses. Very few (~1&) are violent enough to lift or completely demolish sturdy buildings and can last more than two hours
Path A tornado moves along with its thunderstorm, it travels fast and weaves a path that is impossible to predict Tornado watch When the weather conditions might produce tornadoes. Tornado warning When a tornado has been detected
Hurricanes Most powerful storms on Earth Different names –Typhoons – Pacific Ocean –Cyclones – Indian Ocean Form over warm tropical oceans –5 o – 20 o North and South Vary in size –160 km to 1,500 km in diameter Can travel thousands of miles
Formation of Hurricanes Hurricane Season – August to October Begins as a group of thunderstorms Energy –Comes from condensed water vapor –Energy moves from ocean water into the air Strong Winds Develop –Coriolis effect bends the wind Fuel –Direct contact with warm ocean water Hurricanes will continue to grow until they lose their source of warm, moist air
Effects of Hurricanes Wind Speed –120 km/h to 300 km/h Can cause damage in a variety of ways Lift Cars Produce tornadoes Uproot Trees Tear roofs off buildings Heavy rains cause rivers to overflow When a hurricane moves into a coastal area it causes a storm surge –Storm surges can rise sea level and have large waves (1m to 8m) National Hurricane Center tries to warn people in time.
Winter Storms Formed when two air masses collide. A continental polar air mass forming over snow is especially cold, dry, and dense. –It forces moist air to rise very quickly.
Blizzards A storm with falling or blowing snow, winds at least 35 mph, reduced visibility and intense cold. Occur in many parts of the Northern and Central United States.
Formation of a Blizzard 1.When warm air collides with cold air and is forced to rise above the colder air, the warm air brings moisture. 2.This moisture is formed normally by the wet air moving from the South or by blowing across large bodies of water. 3.A lift is created to raise moist air to form clouds and create ice and snow.
Duration of a Blizzard For a storm to be considered a blizzard it has to last at least 3 hours. Some blizzards can last for a few hours or even days!
Dangers of Blizzards Whiteout conditions make it hard to see when traveling. Strong winds and cold temperatures can create dangerous wind chill temperatures. Roads can be slippery to drive on. Power outages can occur due to strong winds and heavy snow. Pipes can freeze and fuel sources can be cut off.
Dust Storm Strong, violent winds that carry fine particles like silt, clay, sand and dust-filled air over an extensive area.
Formation of a Dust Storm Any area with a lot of dust and sand particles –Need dry air – No precipitation or water vapor in the air –Lots of wind Huge –Can spread over hundreds of miles Powerful –Wind speeds of at least 25 miles per hour (40 km)
Dangers of a Dust Storm Arrive without warning Create large wall of dust and debris. Last only a few minutes Leave debris behind Hard to see during storm Breathing is impacted. Takes fertile top soil away and reduces future crops. Current crops are covered with dust.