Mild precipitation and seasonal changes in weather canbe easy for us to handle. However, severe weather can bea dangerous force, leaving destruction in its path.

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CHAPTER FOUR

STORMSSTORMS

Heavy lightning can cause power to go out.

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Lightning and ThunderBoom! Have you ever heard

the rumble of thunder andwondered why it happened?Lightning, created by theelectricity in clouds, heats the airaround it. The air moves sosuddenly that it makes a crashingsound, like an explosion. Lighttravels much faster than sound.That is why we often hear thethunder after we have seen thelightning. The farther away thelightning is, the longer it willtake to hear the thunder.

Calculate thedistance oflightning

You can easilyfigure out about howfar away lightning isfrom where you are.Light travels muchfaster than sound.You may see lightningright away, but thesound of the thundertravels five miles persecond. So, when yousee lightning, begincounting the secondsuntil you hear thethunder. “One-onethousand, two-onethousand, three-onethousand...Boom!”Stop counting whenyou hear the thunder.Then, divide yourtotal seconds by fiveto determine abouthow many miles awaythe lightning is.

Thunder follows lightning.

FrontsStorms often occur when large bodies of air, called air

masses, collide. Warm and cold air masses confront eachother over the land. The place where they meet is called a front.

A cold front occurs when a cold air mass is pushingagainst a warm air mass. The opposite condition would bea warm front. A cold front moves quickly and plungesbeneath warm air, often causing heavy rain or snow. Thesestorms are usually followed by cooling temperatures. Awarm front can also cause rain and temperature changes,but much more slowly.

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A satellite view of a frontal system moving over the United States.

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FloodsHeavy rains often bring the danger and destruction of

flooding. Flash floods can occur in areas where creeks andother smaller waterways flow into larger rivers. After just afew hours of heavy rain, water levels can rise dramaticallyand thrust a powerfulwall of water intosurrounding towns.

Other floods, liketsunamis, can bepredicted in advance.Tsunamis are giantwaves caused byundersea events likeEarthquakes,volcanoes, orlandslides. Tsunamis,sometimes called tidalwaves, can causeenormous damage tocoastal areas.

Severe flooding has submerged these cars.

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TornadoesTornadoes are violent windstorms that occur when

warm, moist air rises quickly toward cool air. Mosttornadoes are funnel-shaped, but tornadoes can come inmany different shapes and sizes. The rapidly swirling airoccurs during a thunderstorm and stretches from the

thunderstorm to theground.

According to theNational Oceanic andAtmosphericAssociation (NOAA),there are about1,000 tornadoesreported in theUnited States eachyear. Thesetornadoes can leavea path of destructionover 1 mile (1.6 km)wide and 50 miles(80 km) long.

A tornado leaves a path of destruction.

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Hurricanes Hurricanes are severe tropical storms that form over the

ocean and often traveltoward land, bringingstrong winds and flooding.In some parts of the world,hurricanes are calledtyphoons or cyclones.

Hurricanes begin astropical storms. Wind andrain rotates in acounterclockwise directionaround the “eye” of thestorm. When winds reach74 miles (119 km) perhour, the tropical stormbecomes a hurricane.

Hurricane force winds.

The aftermath of a hurricane.

Categories of HurricanesThere are five categories of hurricanes, mainly

determined by the strength of the winds and the amountof potential damage to structures. It is known as theSaffir-Simpson Scale.

Category 1: 74-95 mph (119-153 km/h) winds: very limiteddamage to structures

Category 2: 96-110 mph (154-177 km/h) winds: generallyminor damage to structures

Category 3: 111-130 mph (178-209 km/h) winds:considerable damage to small structures

Category 4: 131-155 mph (210-250 km/h) winds:considerable damage to most structures

Category 5: winds over 156 mph (251 km/h): considerabledamage to structures; devastating loss to small structuresand mobile homes

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Hurricanes are classified by the strength of their winds.

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BlizzardsHurricanes are confined to tropical regions, but colder

areas sometimes experience dangerous winter stormscalled blizzards. Strong winds and snowfall create adangerous environment where people cannot see throughthe blowing snow, and “whiteout” conditions often occur.

Sometimes blizzards are not made of falling snow, butof snow that has been picked up from the ground bystrong winds. These storms are called ground blizzards.

Heavy blizzards can cause whiteouts.

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This street and all the cars parked on it are covered in deep snow due to a blizzard.

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