The Rain ShadowThe Rain Shadow

Our Learning Target:Our Learning Target:Describe the rain shadow effect Describe the rain shadow effect and how it influences vegetation and how it influences vegetation

in Washington State.in Washington State.

Weather vs. ClimateWeather vs. Climate

• What is the difference between What is the difference between weather and climate?weather and climate?

•““Climate is what you expect; weather is Climate is what you expect; weather is what you get.”what you get.”

• Climate is what an area receives over Climate is what an area receives over a period of time.a period of time.

• Weather is what we get that day or Weather is what we get that day or week.week.

Weather vs. ClimateWeather vs. Climate

• WeatherWeather refers to the conditions in refers to the conditions in the atmosphere at a given place and the atmosphere at a given place and time OR the day-to-day or short-term time OR the day-to-day or short-term change in atmospheric conditionschange in atmospheric conditions– It includes temperature, atmospheric It includes temperature, atmospheric

pressure, precipitation, cloudiness, pressure, precipitation, cloudiness, humidity, and windhumidity, and wind

Weather vs. ClimateWeather vs. Climate

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

precipitationprecipitation

Weather vs. ClimateWeather vs. Climate

• Climate Climate extends over a long period of extends over a long period of time, whereas time, whereas weather weather is short termis short term– Precipitation includes fresh water Precipitation includes fresh water

falling from the atmosphere as falling from the atmosphere as rain, snow, sleet or hailrain, snow, sleet or hail

– Differences in precipitation are due Differences in precipitation are due to temperature, humidity and to temperature, humidity and location on Earthlocation on Earth

Weather vs. ClimateWeather vs. Climate

• Water exists in three states on earthWater exists in three states on earth– The liquid state is called waterThe liquid state is called water– The solid state is called iceThe solid state is called ice– The gaseous state is called vapor, cloud, The gaseous state is called vapor, cloud,

fog, steam.fog, steam.

Weather vs. ClimateWeather vs. Climate

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

Weather vs. ClimateWeather vs. Climate

• If the air moves high enough, it will If the air moves high enough, it will cool enough to eventually reach its cool enough to eventually reach its dew point, and condensation will dew point, and condensation will begin.begin.

• This is the level at which cloud This is the level at which cloud formation occurs.formation occurs.

Weather vs. ClimateWeather vs. Climate

• Northern hemisphere wind blows east Northern hemisphere wind blows east to westto west

• Westerlies: winds blowing west across Westerlies: winds blowing west across Pacific Ocean to the United StatesPacific Ocean to the United States

• Moist air pushed up coastal mountainsMoist air pushed up coastal mountains• When the warm air is pushed up When the warm air is pushed up

several things occurseveral things occur– Air coolsAir cools– Moisture condenses and becomes heavyMoisture condenses and becomes heavy

The Rain ShadowThe Rain Shadow

• As the Westerlies As the Westerlies hit the state of hit the state of Washington they Washington they rise to go over the rise to go over the Olympics.Olympics.

• As the clouds rise As the clouds rise they cool and they cool and condense causing condense causing rain to fall.rain to fall.

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

Windward side of the mountains

Leeward Side or

“protected” side of the mountains

The Rain ShadowThe Rain Shadow

• Rain shadowsRain shadows exist on the dry side exist on the dry side of mountainsof mountains– They do not get much rain due to They do not get much rain due to

the mountains blocking the rainthe mountains blocking the rain– Deserts are usually located here, or Deserts are usually located here, or

even short grass prairieeven short grass prairie

Windward side of the Mountain

Leeward side of the Mountain

Rain Shadow

Graphic created by EJoyce

The Rain ShadowThe Rain Shadow

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

Rain Rain ForestForest

Evergreen Evergreen ForestForest

Temperate Temperate ForestsForests

Steppe Steppe GrasslandsGrasslands

DesertDesert

Temperate Temperate Pine Pine

ForestsForests

The Rain ShadowThe Rain Shadow• The rain shadowThe rain shadow is a dry region located is a dry region located

on the leeward side of a mountain.on the leeward side of a mountain.• Prevailing winds like Westerlies push clouds Prevailing winds like Westerlies push clouds

into the windward side of mountains. into the windward side of mountains. • A rain shadow area is dry because, as moist A rain shadow area is dry because, as moist

air masses rise to the top of a mountain air masses rise to the top of a mountain range or large mountain, the air cools and range or large mountain, the air cools and the maximum moisture content decreases the maximum moisture content decreases until it reaches the dew point, where the until it reaches the dew point, where the water vapor condenses as rain or snow and water vapor condenses as rain or snow and falls on the windward side or top of the falls on the windward side or top of the mountain. mountain.

The Rain ShadowThe Rain Shadow

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