Severe Storms

Thunderstorms• Occur in warm, moist air masses

and along fronts.• Sinking rain, cooled air, and strong

updrafts of warm air cause strong winds.

• If winds reach 89 km/h or faster, it is a severe thunderstorm.

• Flash floods, strong winds, hail.

Thunderstorms

Lightning• In a storm cloud, warm air is lifted rapidly as

cooler air sinks. This movement causes different parts of the cloud to become oppositely charged.

• When the current flows between opposite charges, lightning flashes.

• Occurs in 3 places: within a cloud, between clouds, cloud and the ground.

Lightning

Thunder• Results from rapid heating of air around

lightning. (Lightning is 30,000 degrees celsius.. 5x the surface of the sun!!)

• The extreme heat causes air around the lightning to expand rapidly. Then it cools and contracts.

• The rapid movement of molecules forms sound waves heard as thunder.

Thunder

Tornadoes• A violently rotating column of air in contact

with the ground.• In severe thunderstorms, wind at different

levels blow at different direction and speed. This is called wind shear.

• Rips apart building, uproot trees, blow through glass. Can lift animals, cars and houses in the air.

Tornadoes

Hurricanes • Large, swirling, low pressure system

that forms over the Atlantic Ocean.• Must have winds of at least 119

km/h.• Category 1-5 (250 km/h)

• Typhoon- forms over the Pacific Ocean.

• Cyclones- Form over the Indian Ocean.

Hurricanes

Images from Space

Strongest Hurricanes

• Begin as low pressure systems west of Africa.• Steered by surface winds.• travel west.• Gains strength from heat + moisture of warm

ocean water. • When it hits land, it loses power and dumps

water.• Strongest winds are within 80 km of the eye.

(50 miles)

Blizzards• Winds at 56 km/h• Blowing snow• Visibility less than 400m• These conditions must persist for 3

hours or more.

Blizzards

National Weather Service

• watch- conditions are favorable• warning- weather exist, take cover!