Weather Factors

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Weather Factors

• Chapter 12, Section 1Notes

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I. Weather Factors

• Weather is defined as the state of the atmosphere
  at a specific time and place
• Describes conditions such as air pressure, wind,
  temperature, and the amount of moisture in air
• Sun provides energy that drives the weather

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I. Weather Factors

• B. 4 main factors that create our weather
• 1. Air temperature
• a. measure of motion of molecules
• 1. when temperature is high, molecules
  move quickly
• 2. when temperature is low, molecules
  move slowly

HOT
COLD
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I. What is weather?

• B. 4 main factors that create our weather
• 2. Wind
• a. due to differences in heating on
• Earth (uneven heating of Earths
  surface)
• 1. Scientific law that air wants to
• be equal
• 2. Warm, expanding air has low
  pressure
• 3. Cooler, denser air has high
• pressure
• b. When air moves from
  high pressure to
• low pressure, there is horizontal movement
  of air
• called wind
• 1. Global winds winds
  that blow over long distances
• 2. Local winds winds that blow over
  short distances

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Wind!

• Always blows from high pressure to low pressure

HIGH
LOW
High Pressure ? Low Pressure
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I. What is weather?

• B. 4 main factors that create our weather
• 3. Humidity
• a. amount of water vapor in the air
• b. measured in grams
• c. warm air can hold more water
• vapor (more space between air
  molecules)
• d. cold air holds less water vapor (less
  space between air molecules)

COLD
WARM
Water Vapor
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I. What is weather?

• B. 4 main factors that create our weather
• 4. Relative Humidity (expressed as percent)
• a. amount of water vapor in the air
  COMPARED to amount needed for saturation at
  a specific temperature
• 1. saturation when air is holding as much
  water vapor as it possibly can
• 2. relative can be thought of as the
  words depends
• a. Amount of humidity depends on the
  temperature of air

COLD
WARM
Water Vapor
Amount of humidity is relative to the temperature
Check this website out!!
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Gizmo on Relative Humidity

• www.explorelearning.com

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(No Transcript)
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II. Dew Point

• Temperature at which air is saturated with water
  vapor condensation forms is the dew point
• Condensation occurs at cooler temperatures
  because there is less space between slow-moving
  cold molecules water vapor molecules collide
  more frequently combine, turning back into
  liquid water

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III. Forming Clouds

• Clouds form as warm air is forced upward,
  expands, and cools
• As air cools, amount of water vapor needed for
  saturation decreases because there is less room
  for water vapor to fit
• As a result, relative humidity increases
• When relative humidity reaches 100, the air is
  saturated with water vapor and condensation takes
  place
• Must have condensation particles/nuclei (solids
  in air salt, dust, smoke, pollen, etc.) in air
  in order for condensation to take place

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IV. Classifying Clouds

• Clouds are classified by shape and height
• 1. 3 types of clouds classified by shape
• a. Stratus
• 1. form layers or smooth, even sheets in
  sky
• 2. usually form at low altitudes
• 3. May be associated with fair weather,
  rain,
• snow
• 4. Stratus cloud near ground is called fog

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IV. Classifying Clouds

• b. Cirrus
• 1. high, thin, white,
• feathery clouds
• 2. made of ice crystals
• 3. associated with fair
• weather but may indicate approaching storms
• 4. Form high in Earths atmosphere

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IV. Classifying Clouds

• c. Cumulus
• 1. Masses of puffy, white
• clouds with flat bases
• 2. Associated with fair
• weather
• 3. Can be up to 18 km
• high

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IV. Classifying Clouds

• b. Height of clouds
• 1. Prefixes used to describe height of
• clouds
• a. cirro high
• b. alto middle
• c. strato low
• 2. Combine prefix with cloud shape to identify
  clouds
• Cirrostratus high stratus clouds
• Altostratus stratus clouds at mid-level

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IV. Classifying Clouds

• Nimbus/Nimbo can be added to cloud to indicate
  precipitation falling out of them
• Cumulonimbus rainy cumulus cloud (suffix)
• Nimbostratus rainy stratus cloud (prefix)

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V. Precipitation

• When clouds droplets combine and grow large
  enough to fall to Earth, it is called
  precipitation
• Air temperature determines what form of
  precipitation falls from clouds
• c. 4 main types of precipitation
• 1. rain raindrops vary in size due to updrafts
  in cloud rate of evaporation
• 2. snow when air temperature is so cold that
  water vapor turns directly to solid
• 3. sleet raindrops pass through layer of
  freezing air near Earths surface, forming ice
  pellets
• 4. hail lumps of ice that forms in
  cumulonimbus clouds when water freezes in layers
  around a small nucleus of ice

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V. Precipitation
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HAIL
Hail Formation Animation