3 Anticipatory setWhat are the four types of fronts? What happens when air masses with different pressure and humidity meet?
4 standardsS 6.4.e – Students know differences in pressure, heat, air movement, and humidity result in change in weather
5 What are the main kinds of storms, and how do they form? The big ideaWhat are the main kinds of storms, and how do they form?
6 Key terms Storm – a violent disturbance in the atmosphere Thunderstorm – a small storm with heavy precipitation and frequent thunder and lightningLightning – 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
7 Key termsTornado – a rapidly whirling, funnel-shaped cloud that reaches down to touch Earth’s surfaceHurricane – a tropical storm that has winds of about 119 kilometers per hour or higherStorm surge – a “dome” of water that sweeps across the coast where a hurricane lands
8 Storms involve sudden changes in air pressure In turn cause rapid air movementsConditions that bring one kind of storm often cause other kinds of storms in the same areaConditions that cause thunderstorms can also cause tornados
9 How thunderstorms form Thunderstorms form in large cumulonimbus cloudsAlso known as thunderheads
10 How thunderstorms form Most cumulonimbus clouds form on hot, humid afternoonsAlso form when warm air is forced upward along a cold frontMany thunderstorms form in the spring and summer in southern states or on the Western Plains
11 Lightning and thunderDuring a thunderstorm areas of positive and negative electric charges build up in the storm cloudsLightning is a sudden spark, or electric discharge, as these charges jump between parts of a cloudSimilar to the shocks you sometimes feel when you touch a metal object on a dry day… but on a MUCH larger scale!
12 Lightning and thunderA lightning bolt can heat the air near it to as much as 30,000 degrees CelsiusMUCH hotter than the sun’s surfaceThe rapidly heated air expands suddenly and explosivelyThunder is the sound of the explosionBecause light travels faster than sound, you see lightning before you hear thunder
13 Thunderstorm damage Can cause severe damage The heavy rains associated with thunderstorms can flood low-lying areasLightning strikes can shatter tree trunks or start forest firesWhen lightning strikes a person it is like a powerful electric shockCan cause burns, unconsciousness, or even heart failure
14 floodsA major danger during thunderstorms is flooding
15 Thunderstorm safetyDuring thunderstorms, avoid places where lightning may strike Also avoid objects that can conduct electricity, such as metal objects and bodies of water
16 Read Thunderstorms on pages 319-320 of your textbook
17 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 surfaceIf it occurs over a lake or ocean it is known as a water spoutAre usually briefMay touch the ground for 15 minutes or lessOnly a few hundred meters acrossWind speeds may approach 500 kilometers per hour
18 Tornados most commonly develop in think cumulonimbus clouds How tornados formTornados most commonly develop in think cumulonimbus cloudsThe same clouds that bring thunderstorms
19 Are most likely to occur How tornados formAre most likely to occurin spring and early summerin late afternoon when the ground is warmThe 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 PlainsA cold, dry air mass moves south from Canada
20 Tornado alleyTornados are rare in CaliforniaAbout 800 occur in the United States every yearView figure 21 on page 321 of your textbook
21 Read Tornadoes on pages 320-321 of your textbook
22 snowstormsAll 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
23 snowstormsIn California, snowstorms generally occur only at high elevationsCalifornians depend on snow to provide part of their fresh water needsSnow that accumulates during the winter melts in the spring and summerThis snowmelt provides fresh water for a variety of needs, including irrigation and electricity production
24 hurricanesA hurricane is a cyclone that has winds of 119 kilometers per hour or higherForm in the Atlantic, Pacific, and Indian oceansIn the western Pacific Ocean, hurricanes are called typhoons
25 How hurricanes formA hurricane begins over warm ocean water as a low-pressure area, or tropical disturbance
26 How hurricanes formA hurricane draws its energy from the warm, humid air at the ocean’s surfaceAs the air rises from the clouds, more air is drawn into the systemThe lower the air pressure at the center of the storm, the faster the winds blow toward the center
27 How hurricanes formHurricane winds are strongest in the narrow band around the center of the stormAt the center is a ring of clouds, called the eyewall, that enclose the quiet “eye”
28 How hurricanes move Hurricanes last longer than other storms Usually a week or moreDuring this time they can travel quite farHurricanes that form in the Atlantic are steered by the trade winds toward the Caribbean islands and the southeastern United StatesAfter a hurricane passes over land, it no longer has warm, moist air to draw energy from, and gradually loses strength
29 Read Hurricanes on pages 324-325 of your textbook
30 Check for understanding What weather conditions are most likely to produce tornadoes? Why do tornadoes occur most often in “tornado alley?”
31 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.
32 What is a hurricane? How do hurricanes form? Guided practiceWhat is a hurricane? How do hurricanes form?
33 Guided practiceWhat 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.