Miss Nelson

SCIENCE ~ CHAPTER 8

WEATHER

Storms

SECTION 4

What are the four types of fronts?

What happens when air masses with different pressure and humidity

meet?

ANTICIPATORY SET

S 6.4.e –Students know differences in pressure, heat, air movement, and humidity result in change in weather

STANDARDS

What are the main kinds of storms, and how do they form?

THE BIG IDEA

Storm – a violent disturbance in the atmosphere

Thunderstorm – a small storm with heavy precipitation and frequent thunder and lightning

Lightning – a sudden spark, or energy discharge, caused when electrical charges jump between parts of a cloud, between nearby clouds, or between a cloud and the ground

KEY TERMS

Tornado – a rapidly whirling, funnel-shaped cloud that reaches down to touch Earth’s surface

Hurricane – a tropical storm that has winds of about 119 kilometers per hour or higher

Storm surge – a “dome” of water that sweeps across the coast where a hurricane lands

KEY TERMS

Storms involve sudden changes in air pressureIn turn cause rapid air movements

Conditions that bring one kind of storm often cause other kinds of storms in the same areaConditions that cause thunderstorms can also cause tornados

STORMS

Thunderstorms form in large cumulonimbus clouds

Also known as thunderheads

HOW THUNDERSTORMS FORM

Most cumulonimbus clouds form on hot, humid afternoons

Also form when warm air is forced upward along a cold front

Many thunderstorms form in the spring and summer in southern states or on the Western Plains

HOW THUNDERSTORMS FORM

During a thunderstorm areas of positive and negative electric charges build up in the storm clouds

Lightning is a sudden spark, or electric discharge, as these charges jump between parts of a cloud

Similar to the shocks you sometimes feel when you touch a metal object on a dry day… but on a MUCH larger scale!

LIGHTNING AND THUNDER

A lightning bolt can heat the air near it to as much as 30,000 degrees Celsius MUCH hotter than the sun’s surface

The rapidly heated air expands suddenly and explosively

Thunder is the sound of the explosion

Because light travels faster than sound, you see lightning before you hear thunder

LIGHTNING AND THUNDER

Can cause severe damage

The heavy rains associated with thunderstorms can flood low-lying areas

Lightning strikes can shatter tree trunks or start forest fires

When lightning strikes a person it is like a powerful electric shock

Can cause burns, unconsciousness, or even heart failure

THUNDERSTORM DAMAGE

A major danger during thunderstorms is flooding

FLOODS

During thunderstorms, avoid places where lightning may strike

Also avoid objects that can conduct electricity, such as metal objects and bodies of water

THUNDERSTORM SAFETY

Read Thunderstorms on pages 319-320 of your textbook

THUNDERSTORMS

One of the most frightening and destructive storms

A rapidly whirling, funnel-shaped cloud that reaches down from a storm cloud to touch Earth’s surface

If it occurs over a lake or ocean it is known as a water spout

Are usually brief May touch the ground for 15 minutes or less

Only a few hundred meters across

Wind speeds may approach 500 kilometers per hour

TORNADOES

Tornados most commonly develop in think cumulonimbus clouds

The same clouds that bring thunderstorms

HOW TORNADOS FORM

Are most likely to occur in spring and early summerin late afternoon when the ground is warm

The Great Plains have the kind of weather pattern that is likely to create tornadosWarm, humid air mass moves north from the Gulf of Mexico into the lower Great Plains

A cold, dry air mass moves south from Canada

HOW TORNADOS FORM

Tornados are rare in California

About 800 occur in the United States every year

View figure 21 on page 321 of your textbook

TORNADO ALLEY

Read Tornadoes on pages 320-321 of your textbook

TORNADOES

All year round, most precipitation begins in clouds as snow

If the air is colder than 0°C all the way to the ground, the precipitation falls as snow

SNOWSTORMS

In California, snowstorms generally occur only at high elevations

Californians depend on snow to provide part of their fresh water needsSnow that accumulates during the winter melts in the spring and summer

This snowmelt provides fresh water for a variety of needs, including irrigation and electricity production

SNOWSTORMS

A hurricane is a cyclone that has winds of 119 kilometers per hour or higher

Form in the Atlantic, Pacific, and Indian oceans

In the western Pacific Ocean, hurricanes are called typhoons

HURRICANES

A hurricane begins over warm ocean water as a low-pressure area, or tropical disturbance

HOW HURRICANES FORM

A hurricane draws its energy from the warm, humid air at the ocean’s surface

As the air rises from the clouds, more air is drawn into the system

The lower the air pressure at the center of the storm, the faster the winds blow toward the center

HOW HURRICANES FORM

Hurricane winds are strongest in the narrow band around the center of the storm

At the center is a ring of clouds, called the eyewall, that enclose the quiet “eye”

HOW HURRICANES FORM

Hurricanes last longer than other storms Usually a week or more During this time they can travel quite far

Hurricanes that form in the Atlantic are steered by the trade winds toward the Caribbean islands and the southeastern United States

After a hurricane passes over land, it no longer has warm, moist air to draw energy from, and gradually loses strength

HOW HURRICANES MOVE

Read Hurricanes on pages 324-325 of your textbook

HURRICANES

What weather conditions are most likely to produce tornadoes?

Why do tornadoes occur most often in “tornado alley?”

CHECK FOR UNDERSTANDING

What weather conditions are most likely to produce tornadoes?Think cumulonimbus clouds along a front are the conditions most likely to produce tornadoes.

Why do tornadoes occur most often in “tornado alley?”The area known as “tornado alley” often has cold dry air meeting warm, moist air.

CHECK FOR UNDERSTANDING

What is a hurricane?

How do hurricanes form?

GUIDED PRACTICE

What is a hurricane?A hurricane is a tropical cyclone with very high winds.

How do hurricanes form?Hurricanes form when low pressure systems form over warm water. The rising warm, moist air adds energy to the system, which eventually becomes a hurricane.

GUIDED PRACTICE

Complete Weather 8-4 Independent Practice

INDEPENDENT PRACTICE