Severe Weather. Thunderstorms Small intense systems that can produce strong winds, rain, lightning...

Severe Weather

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

More…• Thunderstorms get their energy from humid

air• Can produce high winds, flood, or tornadoes

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• 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.

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• Vary in size and 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

• Fuel– Direct contact with warm ocean water

• Hurricanes will continue to grow until they lose their source of warm, moist air

Hurricane Features

Effects of Hurricanes• Wind Speed

– 120 km/h to 300 km/h

• When a hurricane moves into a coastal area it causes a storm surge (raise sea level) and flooding

Winter storms produce snow and ice

• Winter storms are 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

• Very similar to thunderstorms, only the air is rising even higher.

• Warm air has the moisture, and is pushed even higher than normal, passing through clouds that are high in the sky

• Those clouds take some moisture, and it freezes

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!

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 and a lot 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.