Thunderstorms and Thunderstorms and Severe WeatherSevere Weather

13.1 and 13.213.1 and 13.2

ThunderstormsThunderstorms

The intensity and The intensity and duration of duration of thunderstorms thunderstorms depend on local depend on local conditions that create conditions that create them. them.

Thunderstorm factsThunderstorm facts At any given time there are 2000, thunderstorms At any given time there are 2000, thunderstorms

occurring around the world!occurring around the world! Most storms are harmless , but storms are Most storms are harmless , but storms are

responsible for great destruction. responsible for great destruction.

How do thunderstorms form? How do thunderstorms form?

In order for a thunderstorm to form three In order for a thunderstorm to form three conditions must exist.conditions must exist.

1.1. A source of moisture. A source of moisture.

2.2. Lifting of the air mass. Lifting of the air mass.

3.3. An unstable atmosphere. An unstable atmosphere.

MoistureMoisture

In order for storms to In order for storms to form there must be an form there must be an abundance of abundance of moisture in the lower moisture in the lower atmosphere.atmosphere.

The humid air is less The humid air is less dense than the dry air dense than the dry air and is lifted. and is lifted.

The humid air cools The humid air cools and forms water and forms water droplets or cloudsdroplets or clouds

LiftingLifting

A mechanism is needed A mechanism is needed to lift air into cooler to lift air into cooler regions in the regions in the atmosphere. atmosphere.

Examples cold fronts Examples cold fronts push up warmer air, cities push up warmer air, cities or bodies of water can or bodies of water can create a heat source to create a heat source to push up air. push up air.

Only when the water Only when the water vapor condenses can it vapor condenses can it release latent heat and release latent heat and keep the cloud rising. keep the cloud rising.

StabilityStability

If the air remains cooler If the air remains cooler than the rising air mass, than the rising air mass, the unstable conditions the unstable conditions can produce clouds that can produce clouds that grow upwards.grow upwards.

When the density of the When the density of the rising air mass and the rising air mass and the surrounding air are nearly surrounding air are nearly the same, clouds stop the same, clouds stop growing. growing.

Types of ThunderstormsTypes of Thunderstorms

2 major types of 2 major types of Thunderstorms areThunderstorms are

1. Air-Mass 1. Air-Mass ThunderstormsThunderstorms

2. Frontal 2. Frontal Thunderstorms.Thunderstorms.

Air-Mass Thunderstorms:Air-Mass Thunderstorms: A type of thunderstorm in which air rises A type of thunderstorm in which air rises

because of unequal heating of Earth’s surface because of unequal heating of Earth’s surface with in a single air mass and is most common with in a single air mass and is most common during the afternoon and evening. during the afternoon and evening.

2 Types of Air-mass 2 Types of Air-mass ThunderstormsThunderstorms

1.1. Mountain Mountain Thunderstorms: Thunderstorms: occurs when an air occurs when an air mass rises from low mass rises from low elevation to a high elevation to a high elevation, which elevation, which involves air moving involves air moving up the side of a up the side of a mountain. mountain.

(Mountain barrier)(Mountain barrier)

2. Sea- breeze 2. Sea- breeze Thunderstorm: Local Thunderstorm: Local air-mass air-mass thunderstorm that thunderstorm that commonly occurs commonly occurs along a coastal area along a coastal area because land and because land and water store and water store and release thermal release thermal energy differently. energy differently.

Frontal thunderstormsFrontal thunderstorms A type of thunderstorm usually produced by an advancing A type of thunderstorm usually produced by an advancing

cold-front, which can result in a line of thunderstorms cold-front, which can result in a line of thunderstorms hundreds of kms long or more rarely an advancing warm hundreds of kms long or more rarely an advancing warm front, which can result in a relatively mild thunderstorm. front, which can result in a relatively mild thunderstorm.

Thunderstorms develop in three Thunderstorms develop in three stages. stages.

1.1. Cumulus StageCumulus Stage

2.2. Mature StageMature Stage

3.3. Dissipation StageDissipation Stage

Cumulus StageCumulus Stage

Air starts to rise vertically Air starts to rise vertically creating updrafts that creating updrafts that which transport water which transport water vapor to cooler upper vapor to cooler upper regions in the cloud.regions in the cloud.

As water condenses the As water condenses the clouds become larger and clouds become larger and heavier until updrafts can heavier until updrafts can no longer sustain them no longer sustain them and they fall back to and they fall back to Earth as precipitation. Earth as precipitation.

Mature StageMature Stage

Updrafts and downdrafts Updrafts and downdrafts exist side by side. exist side by side.

Precipitation cools the air, Precipitation cools the air, the new cool air sinks the new cool air sinks rapidly causing down rapidly causing down drafts. drafts.

The updrafts and down The updrafts and down drafts form a convection drafts form a convection cells which cause winds cells which cause winds to develop. to develop.

DissipationDissipation

Once the supply of Once the supply of warm air is used up warm air is used up convection stops. convection stops.

The cool downdrafts The cool downdrafts spread out and spread out and eventually stop. eventually stop.

The storm eventually The storm eventually dissipates or dies out. dissipates or dies out.

What causes lightning What causes lightning

Lightning is the transfer of electricity Lightning is the transfer of electricity generated by the rapid rushes of air in a generated by the rapid rushes of air in a cloud. cloud.

Clouds become charged when friction Clouds become charged when friction between the updrafts and downdrafts between the updrafts and downdrafts cause atoms to lose or gain electrons.cause atoms to lose or gain electrons.

Stepped LeaderStepped Leader

Is a channel of Is a channel of partially charged air. partially charged air.

A path of ionized air A path of ionized air which extends which extends downward from the downward from the cloud during the initial cloud during the initial stages of a lightning stages of a lightning strike. strike.

Return StrokeReturn Stroke

A branch channel of A branch channel of positively charged positively charged ions that rushes ions that rushes upward from the upward from the ground to meet the ground to meet the stepped leader. stepped leader.

ThunderThunder

Lightning heats air to Lightning heats air to 30,000 degrees 30,000 degrees Celsius! (5 times the Celsius! (5 times the temperature of the temperature of the Sun’s surface!)Sun’s surface!)

Thunder is the sound Thunder is the sound produced by this produced by this super heating of air super heating of air expanding and expanding and contracting.contracting.

ThunderThunder Because sound travels Because sound travels

more slowly than light you more slowly than light you see lightning before you see lightning before you hear thunder. hear thunder.

Sound travels through air Sound travels through air at about 1100-1200 feet at about 1100-1200 feet (330-350 meters) per (330-350 meters) per second, which is a little second, which is a little more than one mile per more than one mile per five seconds.five seconds.

Time between lightning Time between lightning and thunder / 5 = and thunder / 5 = distance from lightning distance from lightning strike in miles. strike in miles.

Thunderstorms and Lightening Thunderstorms and Lightening SafetySafety

Each year Lightening Each year Lightening causescauses 7,500 forest fires7,500 forest fires 300 injuries300 injuries 93 human deaths93 human deaths

Precautions for Thunderstorms and Precautions for Thunderstorms and lighteninglightening

Inside precautionsInside precautions Stay at least a few feet away from Stay at least a few feet away from

open windows, sinks, toilets, tubs, open windows, sinks, toilets, tubs, showers, electric boxes, outlets, and showers, electric boxes, outlets, and appliances. Lightning can flow through appliances. Lightning can flow through these systems and "jump" to a person. these systems and "jump" to a person.

Do not shower or take a bath during a Do not shower or take a bath during a thunder or lightning storm.thunder or lightning storm.

Avoid using regular telephones, except Avoid using regular telephones, except in an emergency. If lightning hits the in an emergency. If lightning hits the telephone lines, it could flow though telephone lines, it could flow though the phone. Cell or cordless phones, the phone. Cell or cordless phones, not connected to the building's wiring, not connected to the building's wiring, are safe to use. are safe to use.

Outside precautionOutside precaution

Crouch down on the balls of your feet Crouch down on the balls of your feet with your feet close together. Keep with your feet close together. Keep your hands on your knees and lower your hands on your knees and lower your head. Get as low as possible your head. Get as low as possible without touching your hands or knees without touching your hands or knees to the ground. DO NOT LIE DOWN! to the ground. DO NOT LIE DOWN!

If you are in a boat and cannot get to If you are in a boat and cannot get to shore, crouch down in the middle of shore, crouch down in the middle of the boat. Go below if possible. the boat. Go below if possible.

If you are on land, find a low spot away If you are on land, find a low spot away from trees, metal fences, pipes, tall or from trees, metal fences, pipes, tall or long objects. long objects.

If you are in the woods, look for an If you are in the woods, look for an area of shorter trees. Crouch down area of shorter trees. Crouch down away from tree trunks. away from tree trunks.

Severe Weather 13.2 pg 350Severe Weather 13.2 pg 350

All thunderstorms produce wind, rain and All thunderstorms produce wind, rain and lightning, which can have dangerous and lightning, which can have dangerous and damaging effects under certain damaging effects under certain circumstances. circumstances.

Supercells Supercells

Self-sustaining, extremely powerful storm. Self-sustaining, extremely powerful storm. Supercells are characterized by intense, Supercells are characterized by intense,

rotating updrafts taking 10 to 20 mins to rotating updrafts taking 10 to 20 mins to reach the top of the cloud. reach the top of the cloud.

Super storms can last for hours and have Super storms can last for hours and have updrafts as strong as 240 km/hr!updrafts as strong as 240 km/hr!

HailHail

Tornadoes!Tornadoes!

Tornado: a violent, Tornado: a violent, whirling column of air in whirling column of air in contact with the ground. contact with the ground.

If the tornado never If the tornado never reaches the ground it is reaches the ground it is called a funnel cloud. called a funnel cloud.

Tornados are visible Tornados are visible because of the debris because of the debris picked up by the swirling picked up by the swirling column of air or vortex. column of air or vortex.

Development of TornadoesDevelopment of Tornadoes

Tornadoes most often form at the leading Tornadoes most often form at the leading edge of an advancing cold front or along a edge of an advancing cold front or along a line of thunderstorms where winds are line of thunderstorms where winds are converging to a center of very low converging to a center of very low pressure.pressure.

A tornado forms when a vertical cylinder of A tornado forms when a vertical cylinder of rotating air develops in a thunderstorm.rotating air develops in a thunderstorm.

Fujita Tornado Intensity ScaleFujita Tornado Intensity Scale

FTIS: ranks FTIS: ranks tornadoes according tornadoes according to their paths of to their paths of destruction, wind destruction, wind speed and duration. speed and duration.

Tornado DistributionTornado Distribution

Most tornadoes form Most tornadoes form in the spring when in the spring when temperatures temperatures contrasts between contrasts between polar air and tropical polar air and tropical air. air.

Large temperature Large temperature differences occur differences occur frequently over frequently over central United States central United States

Tornado AlleyTornado Alley The main reason the plains in

this area are prone to the more devastating tornadoes than any other region in the US is because this is where cold, dry air flowing south from Canada meets the warm, moist air moving northward from the Gulf of Mexico.

The flat, open lands in these states are prime breeding grounds for tornadoes. Tornadoes cannot grow, stay on the ground, and thrive in mountainous regions or areas with lots of forest.

Texas, Lousiana, Oklahoma, Arkansas, Kansas, Missouri, Iowa, Nebraska,South Dakota, North Dakota and Minnesota.

Tornado SafetyTornado Safety

Average of 80 human deaths and 1500 injuries Average of 80 human deaths and 1500 injuries result from tornadoes every year. result from tornadoes every year.

Tornado Warnings: is an alert issued by Tornado Warnings: is an alert issued by government weather services to warn that government weather services to warn that severe thunderstorms with tornadoes may be severe thunderstorms with tornadoes may be imminent. imminent.

Tornado Watches: is issued when conditions are Tornado Watches: is issued when conditions are right for a tornado to form right for a tornado to form

Tornado PrecautionsTornado Precautions Inside PrecautionsInside Precautions Go at once to a windowless, interior Go at once to a windowless, interior

room; storm cellar; basement; or room; storm cellar; basement; or lowest level of the building lowest level of the building

If there is no basement, go to an inner If there is no basement, go to an inner hallway or a smaller inner room hallway or a smaller inner room without windows, such as a bathroom without windows, such as a bathroom or closet or closet

Get away from the windows Get away from the windows Get under a piece of sturdy furniture Get under a piece of sturdy furniture

such as a workbench or heavy table or such as a workbench or heavy table or desk and hold on to it desk and hold on to it

Use arms to protect head and neck Use arms to protect head and neck If in a mobile home, get out and find If in a mobile home, get out and find

shelter elsewhere shelter elsewhere

If outdoors:If outdoors: If possible, get inside a building If possible, get inside a building If shelter is not available or there is no If shelter is not available or there is no

time to get indoors, lie in a ditch or time to get indoors, lie in a ditch or low-lying area or crouch near a strong low-lying area or crouch near a strong building. Be aware of the potential for building. Be aware of the potential for flooding flooding

Use arms to protect head and neck Use arms to protect head and neck

If in the car:If in the car: Never try to out-drive a tornado in a Never try to out-drive a tornado in a

car or truck car or truck Get out of the car immediately and Get out of the car immediately and

take shelter in a nearby building take shelter in a nearby building If there is no time to get indoors, get If there is no time to get indoors, get

out of the car and lie in a ditch or low-out of the car and lie in a ditch or low-lying area away from the vehicle. Be lying area away from the vehicle. Be aware of the potential for flooding aware of the potential for flooding