Severe Storms. Thunderstorms Occur in warm, moist air masses and along fronts. Sinking rain, cooled...

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!