How much does the climate vary across Washington State?
The first photo is of Olympic National Park by the Pacific Ocean. The area is wet; very, very wet. Moving eastward you find Mt. Baker, one of the Cascades volcanoes. The climate on the mountain is very different from the climate near the ocean. It is extremely cold with abundant snowfall in winter. The third photo is of eastern Washington. Much of the land is farmed. The climate is much drier for two reasons. Can you determine what they are?
Mountains and Climate
Did you ever hike or drive up a mountain? Did you notice that it was cooler near the top? Climate is not just different on a mountain. Just having a mountain range nearby can affect the climate.
Air temperature falls at higher altitudes. You can see this in Figure below. Why does this happen? Since air is less dense at higher altitudes, its molecules are spread farther apart than they are at sea level. These molecules have fewer collisions, so they produce less heat.
Air temperature drops as you go higher.
Look at the mountain in Figure below. The peak of Mount Kilimanjaro, Tanzania (Africa, 3° south latitude) is 6 kilometers (4 miles) above sea level. At 3°S it’s very close to the equator. At the bottom of the mountain, the temperature is high year round. How can you tell that it’s much cooler at the top?
Mount Kilimanjaro has very different climates at the top and bottom.
Mountains can also affect precipitation. Mountains and mountain ranges can cast a rain shadow. As winds rise up a mountain range the air cools and precipitation falls. On the other side of the range the air is dry and it sinks. So there is very little precipitation on the far (leeward) side of a mountain range. Figure below shows how this happens.
What role do prevailing winds play in a rain shadow?
- Where air is denser, the air temperature is higher.
- Rainshadow effect occurs on the leeward side of a mountain range.
- Maritime air may become stuck on the windward side of a mountain range. For this reason it is unable to bring cooler air further inland.
Use this resource to answer the questions that follow.
Mountain Effects on Climate at http://www.youtube.com/watch?v=yuvy4nLtWk4&feature=player_embedded (5:30)
- What two factors can affect climate on mountains?
- What occurs on the windward side of a mountain?
- Describe the climate on the windward side of the mountain.
- Describe the climate on the leeward side of the mountain.
- What are rain shadow deserts?
- Describe the characteristics seen on the windward side of the Sierra Nevada Mountains.
- Describe the characteristics see on the leeward side of the Sierra Nevada Mountains.
- Why does an increase in altitude cause a change in temperature?
- What is rainshadow effect?
- What are the two ways that a mountain range can affect climate?