Severe Weather:Tornadoes and Hurricanes

Thunderstorms and Lightning

S6E4b 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 windsTHE 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.

LOOK

AT

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 damage

Wind 86 to 110 mph. Considerable roof

damage. Winds can uproot trees and

overturn single-wide mobile homes.

Flagpoles bend.

EF-2. Considerable damage

Wind 111 to 135 mph. Most single-wide

mobile homes destroyed. Permanent

homes can shift off foundation. Flagpoles

collapse. Softwood trees debarked.

EF-3. Severe damage

Wind 136 to 165 mph. Hardwood trees

debarked. All but small portions of houses

destroyed.

EF-4. Devastating damage

Wind 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, 2008

Catastrophic 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 millibars

Is 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:

Moisture

Unstable Air

Lift

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.