Storms Chapter 13 Section 4

Essential Questions Chap 13 Sec 4 What are the main kinds of storms, and how do they form? What measures can you take to ensure safety in a storm?

Storms

Storms A storm is a violent disturbance in the atmosphere It is involves sudden changes in air pressure, which can cause rapid air movements There are several types of storms

Types of Storms Thunderstorms Tornadoes Snow Storms Hurricanes

Thunderstorms

Thunderstorms Thunderstorms are small storms with heavy precipitation and frequent thunder & lightning Many thunderstorms form in the spring and summer in southern states and on the Western Plains Thunderstorms form in large cumulonimbus clouds (either on hot, humid afternoons or when cold fronts pass through)

How thunderstorms form: Warm, humid air rises rapidly The air cools, forming dense thunderheads (cumulonimbus clouds) Heavy rain and sometimes hail falls The clouds contain strong upward and downward winds (called updrafts and downdrafts) Thunderstorms contain thunder & lightning

Stages in the Development of a Thunderstorm Makes no sense without caption in book

Thunder & lightning Lightning is a sudden spark (an electrical discharge) as positive and negative charges jump between parts of a cloud, between nearby clouds, or between a cloud and the ground Thunder is caused by the superfast heating of the air by lightning Lightning heats the air around it to 30,000° C (much hotter than the surface of the sun) The rapidly heated air expands suddenly and explosively Thunder is the sound of the explosion Because light travels much faster than sound, you see lightning before you hear thunder

Calculate the distance of lightning: Count the number of seconds between the moment you see the lightning and when you hear the thunder Divide that number by 5 to get the approximate distance in miles Example: 15 seconds divided by 5 = 3 miles Do this inside!!!!!!!

Damage & Danger from Thunderstorms: Heavy rains can cause flooding Lightning can strike and damage trees, homes, electronics in our homes, animals, and people Lightning can start fires When it strikes people and animals, it can cause unconsciousness, serious burns, or even heart failure

Floods Floods are caused by too much water pouring into streams and rivers at once In cities floods can be caused by lack of ground to absorb the water (covered with roads, buildings, etc) If the ground is already soaked because of previous rains it is more likely to flood Floods can destroy human structures and wildlife habitats Floods can be good! They can provide rich new soil for agriculture

Safety during Thunderstorms Go inside Avoid touching telephones, electrical appliances, or plumbing fixtures (all conduct electricity) Cars are generally safe if they have a hard top because the electricity will flow along the metal surface of the car to the ground Avoid metal objects, tall structures, and bodies of water such as: Trees, poles, high hills, fences, being in pools or lakes (even in a boat) Get in a low area as close to the ground as possible

Tornadoes

All About Tornadoes A frightening and destructive storm A rapidly whirling, funnel-shaped cloud that reaches down from a storm cloud to touch Earth’s surface A waterspout is a tornado over a lake or ocean Tornadoes usually touch the ground for 15 minutes or less and are usually only a few hundred meters across Winds in the tornado reach up to 500 kilometers per hour (311 mph)

How Tornadoes Form Tornadoes usually develop in cumulonimbus clouds just like thunderstorms, but can develop in any situation that produces severe weather They are most likely to occur in the spring and early summer, often late in the afternoon when the ground is warm (just like thunderstorms)

Formation continued A special situation on the Great Plains creates perfect weather for tornadoes to form A 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 When the air masses meet, the cold air moves under the warm air, forcing it to rise A squall line (narrow band of thunderstorms) is formed and the storms travel from southwest to northeast A single squall line can produce ten or more tornadoes

Tornado Alley The US has more tornadoes per year than any other country (about 800) Tornadoes occur in nearly every part of the US Because of the warm air from the Gulf of Mexico and the cold air from Canada, there is Tornado Alley It includes Texas, Oklahoma, Kansas, Nebraska, and Iowa (and a very small area of South Dakota). See page 453 for a map.

Tornado Safety The safest place to be is in a storm shelter or the basement of a well-built building Stay away from windows and doors and avoid flying debris Lie on the floor under a sturdy piece of furniture (such as a strong table) Outside – lie flat in a ditch Don’t take cover under an overpass or bridge (the forces are actually strengthened here) There is usually little warning of a tornado – take shelter immediately if you hear of a warning

20.3 Severe Storms Tornadoes  Tornado Intensity  Tornado Safety • Because tornado winds cannot be measured directly, a rating on the Fujita scale is determined by assessing the worst damage produced by the storm.  Tornado Safety • Tornado watches alert people to the possibility of tornadoes in a specified area for a particular time. • A tornado warning is issued when a tornado has actually been sighted in an area or is indicated by weather radar.

Fujita Tornado Intensity Scale Makes no sense without caption in book

Snowstorms

Snowstorms All year, 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. A snowstorm has high winds blowing the snow and even picking up snow from the ground and blowing it back into the air It is easy to become lost in a snowstorm because of poor visibility Strong winds cool a person’s body rapidly

Snowstorm Safety Try to find shelter from the wind Cover exposed parts of your body and try to stay dry If in a car, only run the engine if the exhaust pipe is clear of snow

Hurricanes

Satellite View of Hurricane Floyd Makes no sense without caption in book

Hurricane A tropical cyclone (remember from last week) that has winds of 119 km/h (kilometers per hour) or (74 mph) A typical hurricane is about 600 km (373 miles) across Hurricanes form in the Atlantic, Pacific, and Indian oceans Called typhoons in the western Pacific Ocean Called cyclones in the Indian Ocean

How Hurricanes Form A hurricane begins over warm ocean water as a low-pressure area (called a tropical disturbance) If the tropical disturbance grows in size and strength it becomes a tropical storm, then can become a hurricane Hurricanes that strike the US usually form in the Atlantic Ocean north of the equator near Africa in August, September, or October

Formation Continued Warm, humid air at the ocean’s surface rises and forms clouds The rising air draws more warm, moist air into the system Inside the storm are bands of very high winds and heavy rain Winds spiral inward toward the area of lowest pressure at the center The lower the air pressure at the center of a storm, the faster the winds blow toward the center Hurricane winds may be as strong as 320 km/h (199 mph)

Structure of the Hurricane The hurricane has bands of very high winds and heavy rains The narrow band around the center of the storm has the strongest winds At the center of the storm is a ring of clouds called the eyewall which encloses a quiet “eye” The winds get stronger as the eye approaches When the eye arrives, the weather suddenly changes to calm air and possibly clear skies After the eye passes, the storm resumes, but the wind blows from the opposite direction

Cross Section of a Hurricane Makes no sense without caption in book

How Hurricanes Move Hurricanes last much longer than other storms (usually a week or more) They travel a far distance over the ocean before making “Landfall” Hurricanes formed in the Atlantic Ocean are steered by trade winds toward the Caribbean Islands and the southeastern US (that is us!) After a hurricane moves over land, it loses its supply of warm, humid air and gradually loses strenght Even after losing strength, it can carry heavy rainfall for long distances over several days

Hurricane Damage Hurricanes bring high waves, severe flooding, damaging winds, and even tornadoes as they come ashore In the area of the hurricane while over the ocean, low pressure and high winds can raise water up to 6 meters (20 feet) above normal sea level As the hurricane makes landfall, a huge dome of water called a storm surge sweeps across the coast where the hurricane lands Storm surge is the most deadly part of a hurricane where it makes landfall Storm surges can cause great damage, washing away beaches, destroying buildings along the coast, and eroding coastlines

Hurricane Safety Prior to the 1950s people had little warning about hurricanes because of a lack of technology Today, we watch hurricanes move across the ocean for days Cities will issue hurricane warnings when hurricane conditions are expected with 24 hours Citizens are often told to evacuate which means they should leave the area immediately

20.3 Severe Storms Hurricanes  Hurricane Intensity • The intensity of a hurricane is described using the Saffir-Simpson scale. • A storm surge is the abnormal rise of the sea along a shore as a result of strong winds.

Saffir-Simpson Hurricane Scale Makes no sense without caption in book

Essential Questions Answered Chap 13 Sec 4 What are the main kinds of storms, and how do they form? Thunderstorms – form when warm, humid air rises quickly Tornadoes – form in cumulonimbus clouds Hurricanes – form in low-pressure areas over the ocean Snowstorms – form when it is really cold, windy, and snowing

Essential Questions Chap 13 Sec 4 What measures can you take to ensure safety in a storm? Thunderstorm – stay inside, avoid water & electricity Tornadoes – storm cellar, basement, avoid cars, windows, and doors Hurricanes – evacuate Snowstorms – find shelter, no exposed body parts

Section 5 – Predicting the Weather

Essential Questions (Ch 13 S 5) How do weather forecasters predict the weather?

Collect Data Collect data about clouds, air pressure, and other weather readings Analyze the data to predict what will happen next Meteorologists are scientists that study the causes of weather and try to predict it They use maps, charts, and computers to analyze weather data and to prepare weather forecasts Data is collected by local weather observers, instruments carried by balloons, satellites, and weather stations around the world The National Weather Service owns much of the equipment and provides data to the meteorologists

You can collect data too: Observe air pressure. Falling air pressure usually indicates an approaching low-pressure area, possibly bringing rain or snow Observe clouds. Thin cirrus clouds high in the sky indicate a warm front may be approaching. Cumulus clouds growing taller and taller on a warm afternoon can become cumulonimbus clouds and produce thunderstorms A red sky at sunrise might indicate an approaching low-pressure area and stormy weather A red sky at sunset often indicates storms are moving away and clear weather is ahead

Weather Maps The National Weather Service assembles weather maps using data from all over the country Isobars are lines often found on weather maps. These lines show areas having the same air pressure. Iso means equal and bar means pressure. Measurement may be in inches or mercury, millibars, or both. Isotherms show areas have the same temperature. Weather maps have symbols to show fronts, areas of high and low pressure, types of precipitation, and temperatures See the weather map on page 463

Limits of Weather Forecasts Computers, satellites, and radar have made weather monitoring and predicting much better However, we will probably never be able to predict the weather a month in advance because just a small change today can create big changes several days later

The Butterfly Effect A scientist once suggested that even the flapping of a butterfly’s wings causes a tiny disturbance in the atmosphere. This tiny event might cause a larger disturbance that could grow into a large storm.

Essential Questions Answered (Ch 13 S 5) How do weather forecasters predict the weather? They make observations, collect weather data, and interpret the data to make their predictions

Review What is the name of a scientist that studies and predicts weather? Which type of storm develops over the ocean over warm, humid air? Which type of storm usually develops inside a cumulonimbus cloud over land and has strong, swirling winds? Which type of storm produces heavy rain, thunder, and lightning?