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.