The Rain Shadow

1. 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.

3. 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

4. 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.

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

8. 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.

9. 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

11. 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.

12. 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).

13. Windward side of the mountains Leeward Side or “protected” side of the mountains

14. 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

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

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

18. Temperate Pine Forests Steppe Grasslands Evergreen Forest Temperate Forests Desert Rain Forest

19. 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.

20. The Rain Shadow • As the amount of rain is altered by the geography and the rain shadow the vegetation changes.