Lightning is an electric current. Within a thundercloud way up in the sky, many
small bits of ice (frozen raindrops) bump into each other as they move around in
the air. All of those collisions create an electric charge.
After a while, the whole cloud fills up with electrical charges. The positive charges
or protons form at the top of the cloud and the negative charges or electrons form
at the bottom of the cloud.
Since opposites attract, that causes a positive charge to build up on the ground
beneath the cloud. The grounds electrical charge concentrates around anything that
sticks up, such as mountains, people, or single trees.
The charge coming up from these points eventually connects with a charge
reaching down from the clouds and - zap - lightning strikes!
Lightning can occur between:
Two clouds
Earth and a cloud
Two parts of the same cloud
Tornadoes happen in only 1% of all thunderstorms.
A tornado is a small, spinning column of air that has high wind speeds and low
central pressure and that touches the ground.
A tornado starts out as a funnel cloud that pokes through the bottom of a
cumulonimbus cloud and hangs in the air.
The funnel cloud becomes tornado when it makes contact with the Earth’s surface.
75% of the worlds tornadoes occur in the United States.
Most happen in early spring and summer when cold, dry air from Canada meets
warm, moist air from the Tropics.
The size of a tornado’s path is about 5 miles long and about 30 – 200 feet wide.
Tornadoes have wind speeds from 75-100 mph and more violent tornadoes spin
over 300 mph.
Most tornadoes develop from thunderstorms at the leading edge of a cold front.
Why do you think this happens?
The cool air wedges under the warm air, which may result in wind moving in
opposite directions.
This movement may cause a layer of air to spin. Rapidly rising warm air can turn
the spinning layer into a vertical funnel.
A large, rotating tropical weather system that has wind speeds of at least
120 km/h (75 mph) is a hurricane.
Hurricanes are the most powerful storms on earth.
A Hurricane begins as a group of thunderstorms moving over tropical waters.
Winds traveling in two different directions meet and cause the storm to spin.
Because of the Coriolis Effect, the storm turns counterclockwise in Northern
Hemisphere and clockwise in the Southern Hemisphere.
At higher latitudes, the water is too cold for hurricanes to form.
Hurricanes vary in size from 160 to 1,500 km (99 to 935 miles) in diameter and can
travel for thousands of miles. A hurricane gets its energy from the
condensation of water vapor.
Once formed, the hurricane is fueled through contact with the warm ocean water.
Moisture is added to the warm air by evaporation from the ocean.
As the warm, moist air rises, the water vapor condenses and releases large
amounts of energy. The hurricane continues to grow as long as it is over its source
of warm, moist air.
When it moves over colder waters or land, it begins to die because it has lost its
source of energy. As the most powerful storm in the world, hurricanes cause a lot
of damage when they move onto or near land.
With high winds from 120 km/h (75 mph) to 300 km/h (186 mph) – hurricanes can
knock down trees, destroy buildings and homes.
Yet, most hurricane damage is caused by flooding associated with heavy rains
and storm surges. A STORM SURGE is a wall of water that builds up over the
ocean because of the strong winds and low atmospheric pressure.
The wall gets bigger as it reaches the shore, and it reaches its greatest height when
it crashes onto the shore.
Depending on its strength, a storm surge can be 1 to 8 meters high (26 ft) and
65 to 160 km long (100 miles).
Putting it together --
Write TWO important facts your learned about the following SEVERE WEATHER: