Storms

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Storms

• Chapter 13
• Section 4

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Essential QuestionsChap 13 Sec 4

1. What are the main kinds of storms, and how do
   they form?
2. What measures can you take to ensure safety in a
   storm?

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Storms
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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

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Types of Storms

• Thunderstorms
• Tornadoes
• Snow Storms
• Hurricanes

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Thunderstorms
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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)

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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

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Stages in the Development of a Thunderstorm
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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

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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!!!!!!!

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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

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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

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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

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Tornadoes
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All About Tornadoes

• A frightening and destructive storm
• A rapidly whirling, funnel-shaped cloud that
  reaches down from a storm cloud to touch Earths
  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)

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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)

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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

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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.

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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
• Dont 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

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20.3 Severe Storms
? Tornado Intensity
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.
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Fujita Tornado Intensity Scale
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Snowstorms
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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 persons body rapidly

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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

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Hurricanes
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Satellite View of Hurricane Floyd
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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

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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

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Formation Continued

• Warm, humid air at the oceans 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)

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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

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Cross Section of a Hurricane
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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

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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

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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

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20.3 Severe Storms
? 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.
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Saffir-Simpson Hurricane Scale
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Essential Questions AnsweredChap 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

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Essential QuestionsChap 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

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Section 5 Predicting the Weather
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Essential Questions (Ch 13 S 5)

1. How do weather forecasters predict the weather?

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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

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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

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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

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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

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The Butterfly Effect

• A scientist once suggested that even the flapping
  of a butterflys wings causes a tiny disturbance
  in the atmosphere. This tiny event might cause a
  larger disturbance that could grow into a large
  storm.

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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

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Review

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