The Rain Shadow

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The Rain Shadow

• Our Learning Target
• Describe the rain shadow effect and how it
  influences vegetation in Washington State.

2
Weather vs. Climate

• What is the difference between weather and
  climate?
• Climate is what you expect weather is what you
  get.
• Climate is what an area receives over a period of
  time.
• Weather is what we get that day or week.

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Weather vs. Climate

• Weather refers to the conditions in the
  atmosphere at a given place and time OR the
  day-to-day or short-term change in atmospheric
  conditions
• It includes temperature, atmospheric pressure,
  precipitation, cloudiness, humidity, and wind

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Weather vs. Climate

• Climate is the average weather condition that
  occurs at a place over a period of time, usually
  two or three decades
• It includes temperature and precipitation

5
Weather vs. Climate

• Climate extends over a long period of time,
  whereas weather is short term
• Precipitation includes fresh water falling from
  the atmosphere as rain, snow, sleet or hail
• Differences in precipitation are due to
  temperature, humidity and location on Earth

6
Weather vs. Climate

• Water exists in three states on earth
• The liquid state is called water
• The solid state is called ice
• The gaseous state is called vapor, cloud, fog,
  steam.

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Weather vs. Climate

• The process of changing state requires that
  energy is transferred in the form of heat.

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Weather vs. Climate

• If the air moves high enough, it will cool enough
  to eventually reach its dew point, and
  condensation will begin.
• This is the level at which cloud formation
  occurs.

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Weather vs. Climate

• Northern hemisphere wind blows east to west
• Westerlies winds blowing west across Pacific
  Ocean to the United States
• Moist air pushed up coastal mountains
• When the warm air is pushed up several things
  occur
• Air cools
• Moisture condenses and becomes heavy

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The Rain Shadow

• As the Westerlies hit the state of Washington
  they rise to go over the Olympics.
• As the clouds rise they cool and condense causing
  rain to fall.

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• This rain shadow effect makes the western side
  of the mountains very wet (windward side) and
  causes the eastern side of the mountains to be
  very dry (leeward side).

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Windward side of the mountains
Leeward Side or protected side of the mountains
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The Rain Shadow

• Rain shadows exist on the dry side of mountains
• They do not get much rain due to the mountains
  blocking the rain
• Deserts are usually located here, or even short
  grass prairie

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Windward side of the Mountain
Leeward side of the Mountain
Rain Shadow
Graphic created by EJoyce
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The Rain Shadow

• The rain shadow influences the amount of
  vegetation a region will have by altering
  precipitation amounts.

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Temperate Pine Forests
Steppe Grasslands
Evergreen Forest
Temperate Forests
Desert
Rain Forest
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The Rain Shadow

• The rain shadow is a dry region located on the
  leeward side of a mountain.
• Prevailing winds like Westerlies push clouds into
  the windward side of mountains.
• A rain shadow area is dry because, as moist air
  masses rise to the top of a mountain range or
  large mountain, the air cools and the maximum
  moisture content decreases until it reaches the
  dew point, where the water vapor condenses as
  rain or snow and falls on the windward side or
  top of the mountain.

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The Rain Shadow

• As the amount of rain is altered by the geography
  and the rain shadow the vegetation changes.