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Weather. State Objectives 4.c, 4.e, 4.h. . Discussion. What are some ways in which weather affects your everyday life?. What is Weather?. Atmosphere layer of gases surrounding Earth. Weather is the conditions of the atmosphere. Temperature Air Pressure Humidity Wind Clouds

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State Objectives 4.c, 4.e, 4.h.



What are some ways in which weather affects your everyday life?

What is weather

What is Weather?

  • Atmosphere layer of gases surrounding Earth.

  • Weather is the conditions of the atmosphere.

    • Temperature

    • Air Pressure

    • Humidity

    • Wind

    • Clouds

    • Precipitation

    • Main cause for changes in weather is energy from the sun.

Layers of the atmosphere

Layers of the Atmosphere



  • Indicates the amount of heat(kinetic energy) in the atmosphere.

  • Represents the speed of the molecules.

    • The higher the temperature, the faster the air molecules are moving.

  • Warmer air rises and cooler air sinks which causes convection currents.

  • Measured with a thermometer.

    • Standard unit is Fahrenheit (°F)

    • SI Unit is Celsius (°C)

Convection in the atmosphere

Convection in the Atmosphere

Air pressure barometric pressure

Air Pressure/Barometric Pressure

  • Air has weight because it has mass.

  • Air pressure is a measure of the force of air being exerted on a given area of Earth’s surface.

    • As temperature increases pressure decreases.

      • Cool air is more dense, which causes it to sink (high pressure).

    • As altitude increases air pressure decreases.

Weather and air pressure

Weather and Air Pressure

  • Changes in pressure indicated a change in weather is approaching.

    • Lowpressure systems are associated with clouds & precipitation.

    • Highpressure systems are associated with clear skies.

  • Steady pressure indicates current conditions will continue.

  • Measured with a barometer

    in inches of mercury or in millibars.

  • Humidity


    • Amount of water vapor in the air.

    • Relative humidity is a percentage of the amount of water vapor in the air compared to the maximum amount of water vapor it can hold at that temperature.

      • The warmer the temperature the more water vapor it can hold.

      • Saturated means the air is holding 100% of the water vapor it can hold at that temperature.

    • Measured with a hygrometer or a psychrometer.

    Relative humidity chart

    Relative Humidity Chart

    Dew point

    Dew point

    • Dew is the water vapor that has condensed on a surface into a liquid.

      • Depends on two factors:

        • Amount of water vapor in the air

        • Temperature near the surface

    • Dew point is the temperature at which water vapor condenses into a liquid.



    • Caused by differences in air pressure

      • Air moves from areas of high pressure to areas of low pressure

    • Wind Speed

      • Measure of how fast the air is moving.

      • Measured with an anemometer.

    • Wind Direction

      • Direction from which the wind is coming, NOT the direction it is blowing

        • Ex. North winds blow from N to S

      • Measured with a wind vane.

    Global wind patterns

    Global Wind Patterns

    • Blow steadily across Earth in paths that are thousands of kilometers long

      • Steer weather in certain directions (usually west to east in the U.S.)

    • Caused by thermal energy from the sun

      • The sun does not heat the surface evenly causing uneven heating of the atmosphere.

    Global winds

    Global Winds

    Types of global winds

    Types of Global Winds

    • Surface winds at low altitudes:

      • Trade winds: blow from east to west near the equator.

      • Westerlies: blow from west to east in the mid-latitudes.

      • Coriolis Effect: Earth’s rotation causes winds to curve to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

    Types of global winds1

    Types of Global Winds

    • Jet streams at high altitudes are bands of strong winds (up to 350 km/h) near the top of the troposphere at the northern and southern boundaries of the prevailing westerlies.

      • Race from west to east



    • Clouds form when air rises, cools, and condenses. They are classified according to their height and shape.

    Types of clouds

    Types of Clouds

    • 1. cumulus- a low, puffy cloud that forms on sunny days when heat from the surface causes warm air to rise.

    • 2. stratus- a low, gray, sheet-like cloud that forms when warm, moist air moves over cooler ground. They are seen most often during the winter and may bring steady rain.

    Cumulus and stratus

    Cumulus and Stratus

    Types of clouds1

    Types of Clouds

    • 3. cumulonimbus (thunderheads) - vertical clouds that may be over four miles tall. They form where cold air forces warm air to rise quickly.

    • 4. cirrus- high, featherlike clouds. They are the highest clouds in the sky. They do not produce precipitation.

    Cumulonimbus and cirrus

    Cumulonimbus and Cirrus



    Precipitation – occurs when drops of water or crystals of ice become too large to be suspended in a cloud and fall in the form of rain, freezing rain, sleet, snow, or hail.

    The water cycle

    The Water Cycle

    • Earth’s surface is about 70% water and it exists in all three states.

    • The water cycle is the constant movement of water on Earth.

    • The Sun provides the energy for the water cycle.

    Parts of the water cycle

    Parts of the Water Cycle

    • 1. Evaporation occurs when water changes from a liquid into a gas after gaining heat energy from the Sun.

    • 2. Transpiration is the evaporation of water from the leaves of plants.

    Parts of the water cycle1

    Parts of the Water Cycle

    • 3. Condensation occurs when water vapor changes into liquid water to form clouds or fog.

    • 4. Precipitation occurs when water droplets fall to Earth.

    What is an air mass

    What is an Air Mass?

    • An airmassis a large body of air that develops over a particular region.

    • It has characteristics of the area over which it develops.

    • Cold, dry air masses come from Canada and warm, dry air masses develop over Mexico.

    Air masses

    Air Masses

    Air mass locations

    Air Mass Locations



    • A front is a boundary between two air masses.

    • When two fronts meet, the cold air mass will move under the warm air mass because the cold air is more dense.

    Types of fronts

    Types of Fronts

    • 1. A coldfront forms when a cold air mass pushes under a warm air mass. Cumulus clouds form and thunderstorms may occur.

    • 2. A warm front forms when a warm air mass moves up and over a cold air mass. Cirrus and stratus clouds form and light, steady precipitation occurs.

    Warm and cold fronts

    Warm and Cold Fronts



    Types of fronts1

    Types of Fronts

    • 3. A stationary front forms when a warm air mass meets a cold air mass but neither advances.

    • 4. An occluded front forms when a fast-moving cold air mass overtakes a slower warm air mass. Weather is similar to, but less severe than, the weather along a cold front.

    Stationary and occluded

    Stationary and Occluded





    • A scientist that studies the weather & uses the data to make predictions about weather.

      • Observe patterns & create weather maps

    • A weather forecast is a prediction of present conditions based on observations and data.

    Weather maps

    Weather Maps

    • Satellite map: allow meteorologists to monitor weather on the global scale

    • Radar Map: uses electromagnetic waves to monitor velocity and altitude.

    Types of maps

    Types of Maps

    Weather map symbols

    Weather Map Symbols

    Weather map symbols1

    Weather Map Symbols



    Severe weather

    Severe Weather

    • Thunderstorms: brief, intense storms produced by rapidly rising clouds.

      • May produce hail

      • Lightning is huge electrical discharges.

  • A tornado is a violent, whirling wind that moves in a narrow path over land.

  • Tornadoes


    Tornado damage


    Watches and warnings

    Watches and Warnings

    • A watch is issued when conditions are favorable for severe weather to occur.

    • A warning is issued when severe weather has been sighted.

    • The National Weather Service monitors weather and issues watches and warnings when appropriate.

    What is a hurricane

    What is a Hurricane?

    • A hurricane is a low-pressure system that forms over tropical oceans.

    • Also called typhoons or tropical cyclones.

    • Named for the Mayan god Hurakanwho blew his breath across the water.

    Disturbances depressions and storms

    Disturbances, Depressions, and Storms

    • A tropical disturbance is an area of organized convection that originates in the tropics. It has no eye or rotation.

    • A tropical depression is a cyclone that has a maximum wind speed of 38 mph.

    • A tropical storm has a wind speed between 39 mph and 73 mph.

    Conditions required for hurricane formation

    Conditions Required for Hurricane Formation

    • Warm ocean waters of at least 80° F.

    • High humidity in the troposphere.

    • An atmosphere that quickly cools with altitude.

    • A distance of at least 300 miles from the equator.

    • A surface system with convergent winds.

    • Low wind shear. Wind shear is the rate of wind speed or direction change with altitude.

    Hurricane formation

    Hurricane Formation

    Parts of a hurricane

    Parts of a Hurricane

    • The eye is the circular area of calm, relatively light winds at the center of a hurricane. It is the area of lowest pressure.

    • The eyewall is the ring surrounding the eye that contains the highest wind speeds.

    • Rainbands are bands of heavy rain that spiral outward from the storm’s center.

    Parts of a hurricane1

    Parts of a Hurricane

    Where hurricanes form

    Where Hurricanes Form

    When hurricanes occur

    When Hurricanes Occur

    • The Atlantic hurricane season lasts from June 1- November 30.

    • These dates include about 97% of hurricanes.

    • Most occur from August to October.

    When hurricanes occur1

    When Hurricanes Occur

    Tracking hurricanes

    Tracking Hurricanes

    • Hurricanes can be tracked using satellites, radar (near land), and hurricane hunters.

    • Hurricane Hunters is the nickname of the 53rd Weather Reconnaissance Squadron of the Air Force Reserve. They are based in Biloxi, Mississippi.

    • Gathers data including wind direction and speed, pressure, temperature, and humidity from the planes altitude to the water’s surface.

    Paths of hurricanes

    Paths of Hurricanes

    • Depends on where the hurricane forms.

    • Trade winds cause hurricanes to move east to west near the equator.

    • As hurricanes move north, they begin to turn back to the east.

    Hurricane paths

    Hurricane Paths

    Hurricane ike

    Hurricane Ike

    Effects of hurricanes

    Effects of Hurricanes

    • High winds

    • Heavy rain and flooding

    • Tornadoes after landfall

    • Storm surge is the rising wall of water that comes ashore with a hurricane. It causes the most damage and is responsible for 90% of deaths.

    Storm surge

    Storm Surge

    • Storm Surge Animation

    Naming hurricanes

    Naming Hurricanes

    • Hurricanes are named to ease communication between the government, forecasters, and the public.

    • Naming Atlantic storms began in 1953.

    • 2012 List of Names-Alberto, Beryl, Chris, Debby, Ernesto, Florence, Gordon, Helene, Isaac, Joyce, Kirk, Leslie, Michael, Nadine, Oscar, Patty, Rafael, Sandy, Tony, Valerie, and William.

    Rating hurricanes

    Rating Hurricanes

    • The Saffir-Simpson scale is uses wind speed to rate the strength of hurricanes.

    • Category 1- 74-95 mph Minimal

    • Category 2- 96-110 mph Moderate

    • Category 3- 111-130 mph Extensive

    • Category 4- 131-155 mph Extreme

    • Category 5- 156+ mph Catastrophic

    Strongest hurricanes in history

    Strongest Hurricanes in History

    • Typhoon Tip (1979) was the most intense (lowest pressure- 870 mb) hurricane in history.

    • Hurricane Wilma (2005) was the strongest Atlantic hurricane.

    • Typhoon Nancy (1961) had maximum sustained winds (two minute average) of 213 mph.

    Size of typhoon tip

    Size of Typhoon Tip

    • Had a diameter of almost 1,400 miles.

    Path of typhoon tip

    Path of Typhoon Tip

    Hurricane katrina 2005

    Hurricane Katrina (2005)

    • Costliest hurricane in U.S. history ($81 billion in damage).

    • Fifth deadliest hurricane (1,836 deaths)

    • Crossed Florida as a Category 1 but gained strength in the Gulf of Mexico.

    • Made landfall in Louisiana and Mississippi on August 29 as a Category 3.

    Path of katrina

    Path of Katrina

    Katrina from satellite

    Katrina from Satellite

    Katrina damage

    Katrina Damage

    Katrina damage1

    Katrina Damage

    Highway 90 from biloxi to gulfport

    Highway 90 from Biloxi to Gulfport

    Waveland mississippi

    Waveland, Mississippi

    Pass christian middle school

    Pass Christian Middle School

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