Severe Weather: Tornadoes and Hurricanes

Thunderstorms and LightningS6E4b Relate unequal heating of land and water surfaces to form large global

wind systems and weather events such as tornados and thunderstorms.

c Relate how moisture evaporating from the oceans affects the weather patterns and weather events such as

hurricanes

Task:•

• Scenario: You are a team of storm chasers from the Weather Channel. Your job is to educate the public about severe weather as it is happening. You will need a team of researchers to do this project. Each person will play a role, but you will need to do the research on the severe storm alone.

Your Task:• Create a group product to share the

information about your storm with the rest of the class during a “gallery walk.”

• Products could be a song, poster, informational flyer, brochure, 3 minute information video, recipe card or any other product your group comes up with and gets approved by the teacher

As you work think about these questions :

• What are the “ingredients” for your storm to form?• How does your storm form?• What are the atmospheric conditions that are

likely to occur?• Does your storm form during a specific season or

month(s)?• Is there a particular location where this storm

forms?• How does this storm affect the people who live

through it?• What are some safety tips to survive this storm?

Grab Toto!!TORNADOES

•Are a low pressure storm that usually forms over land

•in an average year, 800 tornadoes are reported in the U.S.

•a tornado is defined as a violently rotating column of air extending from a thunderstorm to the ground… the rotating column of air is called the vortex

•the vortex is only visible when debris and dirt gets carried up with the winds

THE HOOK

Where do they come from?

Tornadoes come from the energy released in a thunderstorm.

What makes them dangerous (as compared to hurricanes) is that their energy is concentrated in a small area, only a hundred yards across

When & Where do they occur?

Most common east of the Rocky Mountains and west of the Appalachian Mountains.

They occur mostly during the spring and summer (April-June) They usually occur during the late afternoon and early evening.

Usually happen along cold fronts

How fast do tornadoes move?

Movement can range from virtually stationary to more than 60 miles per hour ... Average is 10-20 miles per hour.

Watch—means conditions are likely for tornado to develop

Warning—means that tornado has been spotted

THE WIND!

• Take a look at this piece of wood that was driven into the palm tree.

LOOKAT

THESE

MEASURING DESTRUCTION

The Enhanced Fujita Scale rates tornadoes based on the amount and type of wind damage produced.

EF-0. Light damage

Wind 65 to 85 mph. Causes some damage to siding and shingles

EF-1. Moderate damageWind 86 to 110 mph. Considerable roof damage. Winds can uproot trees and overturn single-wide mobile homes. Flagpoles bend.

EF-2. Considerable damageWind 111 to 135 mph. Most single-wide mobile homes destroyed. Permanent homes can shift off foundation. Flagpoles collapse. Softwood trees debarked.

EF-3. Severe damageWind 136 to 165 mph. Hardwood trees debarked. All but small portions of houses destroyed.

EF-4. Devastating damageWind 166 to 200 mph. Complete destruction of well-built residences and large sections of school buildings

EF-5. Incredible damage.Wind +200 mph. Significant structural deformation of mid- and high rise buildings.

Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 yards

May 25th, 2008Catastrophic damage was reported in Parkersburg as much of the town was destroyed, with reports of flattened houses and debarked trees. Six people were killed in Parkersburg and at least two fatalities were reported where a housing development was destroyed. At least 70 people were injured

At 9:45 p.m. on May 4, 2007, Greensburg was hit by an EF5 tornado. The tornado was estimated to be 1.7 miles (2.7 km) in width and traveled for nearly 22 miles (35 km). Ninety-five percent of the city was confirmed to be destroyed, with the other five percent being severely damaged. The National Weather Service estimated winds of the tornado to reach 205 mph (330 km/h). This was the first tornado to ever be rated EF5 since the update of the Fujita scale.

HURRICANES

•Low pressure systems that form over warm, tropical waters near the equator

•Most form between 5 and 20 degrees north latitude — they almost never form in the South Atlantic

They have the lowest barometric pressure ever recorded with and storm (905 millibarsIs the lowest recorded

These huge areas of low pressure is what creates The rapid, inward spiraling of winds

When winds have developed speeds from 39 to 73 miles per hour, it is called a tropical storm (storms are given names when they begin to have winds of this speed).

HURRICANE DEVELOPMENT

2005 Katrina Developing

The storm becomes a hurricane when it reaches a wind speed of over 74 mph

Hurricane Formation

THE END OF A HURRICANE

When a hurricane travels over land or cold water, its energy source (warm water) is gone and the storm

weakens, quickly dying.

HURRICANE SEASON

•Occurs from June through November

•Most hurricanes form during the late summer months because the ocean is still retaining heat from the warmer earlier months

MEASURING DESTRUCTION

•We use the Saffir-Simpson scale to rank hurricane intensities

Saffir-Simpson Scale

CATEGORY WIND SPEED STORM SURGE

DAMAGE

1 74-95 mph 4-5 feet Minimal

2 96-110 mph 6-8 feet Moderate

3 111-130 mph 9-12 feet Extensive

4 131-155 mph 13-18 Extreme

5 Greater than 155

Greater than 18

Catastrophic

Video Clip on Wind Tunnel

STORM SURGE ACCOUNTS FOR 90% OF

HURRICANE-CAUSED DEATHS

ThunderstormsA storm containing thunder and Lightning Usually produces heavy wind and Occasionally hail.

Thunderstorms need:MoistureUnstable AirLift

Thunderstorm Formation• Thunderstorms form when warm, humid air

rises in an unstable environment. • A number of things, such as unequal heating

of Earth's surface or lifting of warm air along a front can trigger the upward air movement needed to create thunderstorm-producing cumulonimbus clouds.

• Severe thunderstorms produce high winds, damaging hail, flash floods, and tornadoes.

Tornado Precautions

• Go to a basement, if you have one.• Get in the innermost room of your house.

Avoid rooms with windows. Bathrooms are good.

• Crouch with arms above your head.• If outside, lie in a ditch or get under a

bridge.• If you live in an area with a frequency of

tornadoes, listen to forecasts.

Thunderstorm

• Lightning • Lightning is a charge of

electricity that travels out from a thunder cloud.

• Like electricity, the bolt of lightning moves from the negative to the positive.

• This creates a giant spark.

Have you ever rubbed a balloon against your hair and then placed the balloon on the wall?As you rub the balloon, it gets covered with negative charges. The wall has a positive charge and the balloon has a negative charge. The negative charge is attracted to the positive charge and this is why it sticks to the wall. Opposites attract!

How is this similar to lightning? Lightning is made in a similar way. The electricity moves from the negative towards the positive. Some parts of clouds end up with a lot of negative charges (like the balloon). The earth can have positive charges (like the wall). If the difference between the two is big enough, the negative charge will be attracted to the positive charge. A spark will jump between the cloud and the earth because opposites attract.

Sum Things Up!• Can tornadoes happen anytime or only in

certain times of the year?

• Why do tornados happen most in tornado alley?

What you should Know…Some low pressure systems can give rise to weather events ‐

that are damaging to people, their property, and the land. These incidents can occur almost anywhere and at any time of the year. If the conditions are right for a severe storm to occur, the National Weather Service posts a watch. This means that it is possible to experience the event that the watch is posted for. If the storm is sighted and on its way to you, a warning is posted.