Severe StormsSevere Storms

ThunderstormsThunderstorms

TornadoesTornadoes

HurricanesHurricanes

What are severe storms?What are severe storms?

• They form under very special conditions

• They often grow our of another, more common storm – thunderstorms!

Think about the last time you experienced a thunderstorm. What is associated with a thunderstorm?

ThunderstormsThunderstorms

• Thunderstorms are the most common kind of storm.

• They form in clouds called thunderheads – cumulonimbus clouds!

• They cause huge electrical sparks – lightning!

Thunderstorms con’t.Thunderstorms con’t.

• The lightning heats the air and causes thunder.

• Thunderstorms usually have heavy rains and strong winds.

• Some thunderstorms also produce hail.

Thunderstorm fun facts!Thunderstorm fun facts!

• Thunderstorms are the strongest natural phenomenon. At any given moment, about 2,000 thunderstorms are occurring on Earth. During these storms, lightning strikes Earth as frequently as 100 times every second.

TornadoesTornadoes

• The most violent thunderstorms spin off even more dangerous storms – tornadoes!

• A tornado is a violent whirling wind that moves across the ground in a narrow path.

Tornadoes – How do they happen?Tornadoes – How do they happen?

• When the updraft in a convection cell is really strong, the air rushes in from all sides at high speeds.

• The air curves into a spin. This lowers the air pressure. Air rushes in even faster, which lowers the air pressure even more. The tornado gets faster and faster!

How they happen…con’t.How they happen…con’t.

• As the tornado gets stronger, a funnel forms that eventually touches the ground. Winds can reach up to 300mph in the center of a tornado.

• Tornados move across the ground very fast but can change its direction continually.

Tornadoes – Where they happenTornadoes – Where they happen

• Tornadoes in the US seem to occur in the Midwest and in the South.

• Tornadoes form where dry, cold air masses mix with warm, moist air masses.

• In the US, this is most likely to happen in the Great Plains region and the Mississippi Valley.

• Tornadoes are most likely to occur when there are big differences in the air masses. This happens mostly in early spring and summer.

Hurricanes – How do they form?Hurricanes – How do they form?

• Hurricanes are very large swirling storms with very low pressure at the center.

• They form over tropical oceans – near the equator.

• Air masses near the equator don’t form fronts. Instead they form lots of thunderstorms.

• As global winds push these thunderstorms along, they line up in rows. Strong heating and lots of evaporation over the ocean can cause a large low-pressure center to form.

Hurricane TracksHurricane Tracks

Severe Storms - NotesSevere Storms - Notes

• Thunderstorms are the most common kind of storm.• They form in clouds called thunderheads –

cumulonimbus clouds!• They cause huge electrical sparks – lightning!

• The most violent thunderstorms spin off even more dangerous storms – tornadoes!

• A tornado is a violent whirling wind that moves across the ground in a narrow path.

• Hurricanes are very large swirling storms with very low pressure at the center.

• They form over tropical oceans – near the equator.