Understanding Weather

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Chapter 16

• Understanding Weather

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• Climate
• The average of all weather conditions of an area
  over a long period of time
• Includes temperature, pressure, humidity
• Affected by the angel at which light strikes the
  Earth

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Section 1 Water in the Air

• Water Cycle
• Evaporation, Condensation, Precipitation, Run-Off
• Condensation
• The change of sate from gas to Liquid
• Weather
• Present state of the atmosphere and the current
  conditions in the environment
• Air pressure, wind, temperature, moisture,
  humidity

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• Humidity
• Amount of water vapor in the air
• Depends on the temperature of the air
• As Temp. increases, the amount of water vapor
  that air can hold goes up
• Relative Humidity
• Measure of the amount of water vapor in the air
  compared to what the air could hold ()

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• Dew Point
• Temperature at which air is saturated and
  condensation takes place
• Saturated
• Air is holding all of the moisture it possibly
  can at a particular temperature

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• Clouds
• humid air is cooled to its dew point, the water
  vapor forms drops of water around dust particles

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Clouds

• Cumulus
• Flat bottoms
• Form from warm air rising
• Indicate fair weather
• Cumulonimbus
• Cumulus clouds that have grown larger
• Produce Thunderstorms

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Clouds

• Stratus
• Clouds that form in layers
• Often block out the sun
• Nimbostraus, produce light to heavy rain
• Cirrus
• Thin, Feathery, white clouds
• Form at high Altitudes and Strong winds
• Thinking of Cirrus clouds indicate a change in
  weather

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Cloud Prefixes

• Nimbus
• Likely to produce Precipitation
• Nimbo
• Likely to produce Precipitation
• Cirro
• Describe clouds at High Altitudes
• Alto
• Describe clouds that form at Middle Altitudes

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• Fog
• Air that is cooled to its dew point near the
  ground
• Condenses and forms a stratus cloud
• Status cloud on the ground

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• Precipitation
• falling water drops
• Can form rain, snow, sleet, or hail depending on
  the temperature

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Section 2 Air Masses and Fronts

• Air mass
• A large body of air that has the same properties
  as the surface over which it develops
• Weather is always changing because of the
  constant movement of air and moisture

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Types of Air Masses (North America)

• Warm Air Masses
• Come form Tropical Regions
• Cold Air Masses
• Come from Polar Regions
• Types
• Maritime form over water (Wet Air)
• Continental form over land (Dry Air)

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Air Masses Affect on Weather

• Maritime Polar
• Cold air formed over water
• Wet Cold Air
• Continental Polar
• Cold Air formed over land
• Dry Cold Air

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Air Masses Affect on Weather

• Maritime Tropical
• Warm air formed over water
• Wet Warm Air
• Continental Tropical
• Warm air formed over land
• Dry Warm Air

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• Front
• Boundary that forms between two air masses that
  collide
• Warm air is being cooled to cause precipitation

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Types of Fronts

• Cold Front
• Cold air moving under warm air
• Move quickly

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Types of Fronts

• Warm Front
• Warm air moves over cold air
• Gradually replaces cold air

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Types of Fronts

• Occluded Front
• Warm Air Mass caught between 2 cold air masses
• Stationary Front
• Cold Air mass meets Warm Air mass
• Cold Air mass does not have enough force to lift
  the warm air mass

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Weather Patterns from Fronts

• Warm
• Cirrus followed by stratus clouds, rain and snow
• Bring drizzly rainy conditions
• Warm clear weather follows

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• Cold
• Cumulus and cumulonimbus, rain and thunderstorms
• Bring Thunderstorms, heavy rain, or Snow
• Cooler dryer weather follows

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Weather Patterns from Fronts

• Stationary
• Light winds precipitation
• Brings Many days of cloudy wet weather
• Occluded
• Strong winds and heavy precipitation
• Larges amounts of rain or snow
• Cool Temperatures

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Air Pressure and Weather

• Pressure
• High means clear weather
• Low means cloudy weather, occur along fronts and
  cause most of the weather in the U.S.

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Air Pressure and Weather

• Cyclones
• Low Pressure center
• Winds spiral inward
• Anticyclones
• High Pressure center
• Winds Spiral outward

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Section 3 Severe Weather

• Thunderstorms
• Result from the rapid upward movement of warm
  moist air
• Heavy rain (hail), strong wind, lightning,
  thunder

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Severe Weather

• Lightning
• Electric dischage that take place between two
  oppositely charged surfaces
• Cloud to Ground, Cloud to Cloud, Inside the Cloud
• Thunder
• Sound caused by rapid expansion of air along a
  Lightning Strike
• Strike is 1 mile away if you hear Thunder 5
  seconds after seeing the Lightning Strike

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Tornado

• Violent, whirling wind that moves in a narrow
  path over land,
• Extremely low pressure which causes an updraft
• 75 occur in the USA
• Happen in 1 of Thunderstorms
• Average wind speeds 120-180 km/h

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Hurricane

• Large, swirling, low pressure system that forms
  over oceans
• (120 km/h winds minimum)
• Receives energy from the warm moist air of a body
  of water
• Dies out when it reaches land

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Section 4 Forecasting the Weather

• Meteorologist
• A person who studies the weather
• Watch prepare for severe weather
• Warning take immediate action due to weather

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Tools used to Forecast Weather

• Thermometer
• Indicates tempurture
• Barometer
• Indicates atmospheric pressure
• Anemometer
• Indicates winds speeds
• Occasionally set up with a wind sock or wind vane
  to measure direction

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Tools used to Forecast Weather

• Radar
• Used to find location, movement, of storms
• Can also be used to determine amount of
  precipitation
• Satellites
• Can track storms, measure wind speeds, humidity,
  and temperature at different altitudes inside the
  storm

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• Station Model
• weather maps for larger areas that show the
  information collected by meteorologists in
  specific areas

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• Isotherm
• a line that connects points of equal temperature
• Isobar
• a line drawn to connect points of equal pressure

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