Science ~ chapter 8 weather Miss Nelson

Section 4 Storms

Anticipatory set What are the four types of fronts? What happens when air masses with different pressure and humidity meet?

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

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

Key terms 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

Storms involve sudden changes in air pressure In turn cause rapid air movements Conditions that bring one kind of storm often cause other kinds of storms in the same area Conditions that cause thunderstorms can also cause tornados

How thunderstorms form 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

Lightning and thunder 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

Thunderstorm damage 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

floods A major danger during thunderstorms is flooding

Thunderstorm safety During thunderstorms, avoid places where lightning may strike Also avoid objects that can conduct electricity, such as metal objects and bodies of water

Read Thunderstorms on pages 319-320 of your textbook

tornadoes 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

Tornados most commonly develop in think cumulonimbus clouds How tornados form Tornados most commonly develop in think cumulonimbus clouds The same clouds that bring thunderstorms

Are most likely to occur How tornados form Are most likely to occur in spring and early summer in late afternoon when the ground is warm The Great Plains have the kind of weather pattern that is likely to create tornados Warm, humid air mass moves north from the Gulf of Mexico into the lower Great Plains A cold, dry air mass moves south from Canada

Tornado alley Tornados are rare in California About 800 occur in the United States every year View figure 21 on page 321 of your textbook

Read Tornadoes on pages 320-321 of your textbook

snowstorms 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 needs Snow 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

hurricanes 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

How hurricanes form 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 move 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

Read Hurricanes on pages 324-325 of your textbook

Check for understanding 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.

What is a hurricane? How do hurricanes form? Guided practice 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.

Complete Weather 8-4 Independent Practice