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Thunderstorms
Severe Weather
Thunderstorms are storms with lightning and thunder.
Tornadoes can also form during thunderstorms.
What is a Thunderstorm?
Lightning Lightning is static
electricity.Negatively charged
particles gather in the cloud.
Positively charged particles gather on the ground.
When the difference is large enough, the particles try to connect to each other.
Thunderstorms Form in Three Steps
1. Cumulus Stage Rising humid air
forms a cumulus cloud.
The condensation continues. The updraft keeps the rain particles in the cloud.
The cloud continues building into a cumulonimbus cloud.
Thunderstorms Form in Three Steps
2. Mature StageIce particles form in
the top part of the cloud.
As they get larger they begin to fall and pull cold air down with them.
The strong downdraft brings heavy rain or hail.
Thunderstorms Form in Three Steps3. Dissipation StageThe downpour can
spread out and block any warm air from rising.
The storm slows down and ends.
At a Cold Front
Air is forced up quickly.
This creates a cumulonimbus cloud quickly.
Uneven heating can cause convection thunderstorms.
Remember convection is the rising and falling of air in a cycle.
When do Thunderstorms Form?
Within an Air Mass
Sea Breeze
Sea Breeze
Warm Air
A tornado is a violently rotating column of air stretching from a cloud to the ground.
You cannot see the air moving.What you DO see is the things that the
tornado has picked up or water droplets.
Tornadoes Form in Severe Thunderstorms
More tornadoes occur in North America than any other place in the world.
Warm air from the Gulf of Mexico moves north and meets cold air masses.
Most tornadoesSmall; last only a few minutesMay break branches or ruin billboards
20% of tornadoesKnock over large treesLift cars up
1% of tornadoesCompletely demolish sturdy buildings
Effects of Tornadoes
The path of the tornado is impossible to predict.
The tornado moves at the same pace as the thunderstorm it is attached to.
The National Weather ServiceThe National
Weather Service issues a “tornado watch” when conditions are right to form tornadoes.
A “tornado warning” is issued when a tornado has been detected.