Transcript The Rain Shadow - Boise State University

The Rain Shadow
Our Learning Target:
Describe the rain shadow effect and
how it influences vegetation in
Washington State.
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.
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
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
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
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.
Weather vs. Climate
• The process of changing state requires
that energy is transferred in the form of
heat.
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.
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
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.
• 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).
Windward side
of the
mountains
Leeward Side
or “protected”
side of the
mountains
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
Windward side of
the Mountain
Leeward side of
the Mountain
Rain
Shadow
Graphic created by EJoyce
The Rain Shadow
• The rain shadow influences the amount of
vegetation a region will have by altering
precipitation amounts.
Evergreen
Forest
Rain Forest
Temperate
Pine Forests
Temperate
Forests
Steppe
Grasslands
Desert
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.
The Rain Shadow
• As the amount of rain is altered by the
geography and the rain shadow the
vegetation changes.