Mountain Effect
Take a look at the next three slides and
try to answer the following
• Try to decide why each city has the climate it
does.
• Why does it rain more in certain places than
others?
Seattle, WA
Boston, MA
Las Vegas, NV
Memphis, TN
Austin, TX
Jacksonville,
FL
Seattle, WA
Average Monthly Temperature:
January
40.9
April July October
50.2
65.3
52.7
Annual Amount of Precipitation:
Inches: 37.07
Days: 155
Annual Snowfall: 11.4''
Jacksonville, FL
Average Monthly Temperature:
January
53.1
April July October
66.6
81.6
52.3
Annual Amount of Precipitation:
Inches: 52.34
Days: 116
Annual Snowfall: Trace
Why does it rain more in certain places
than others?
• Mountains near the ocean hold part of the
answer.
• When water evaporates from the ocean, it
becomes water vapor in the air.
• The warm, moist air rises and moves over
land.
• Air that meets mountains is forced to go higher,
where temperatures are colder.
• Clouds form that can drop rain or snow on one side
of the mountain.
• This side is called the windward side (closest to the
ocean/ wind).
• Some of the wettest places on Earth are on the windward
side of mountains.
After the clouds
have dissipated,
the air finally
crosses to the
other side of the
mountain. There
is usually very
little moisture
left.
• Because there is not much moisture left,
clouds are not likely to form. This leaves the
back side of the mountains often dry and
desert-like.
Sierra Nevada Mountain Range
The Sierra Nevada
Mountains
span 400 miles
across CA.
The windward side
(eastern side) of the
Sierra Nevada
Mountains receive
much precipitation
and are lush with
vegetation.
The leeward side (western
side), however, is a very dry
desert region.
What’s the reason for this?
It’s all about the Mountain Effect!
• Why is there little moisture left in the air by
the time it reaches the leeward side of a
mountain?
Most of the
moisture has
already fallen
as
precipitation.
• Why does more rain and snow fall at the top
of a mountain than at its base?
At the base of a mountain, the air is warmer. The
air needs to cool to form clouds that drop
precipitation.
• If you chose G, you are correct!
• The air on the leeward (backside) of the
mountain is drier than on the windward
(front) side of the mountain.
• If you chose J, you are correct!
• The air cools as it rises, causing fog to form.
Notes:
• Water evaporates from the ocean, and it becomes
water vapor.
• This warm, moist air rises and moves over land.
• Clouds form that can drop rain or snow on one side
of the mountain.
• The clouds dissipate, and the air crosses to the other
side of the mountain. There is usually very little
moisture left.
*** In your notes, draw a diagram of a mountain
and the mountain effect.
Review
If you chose J, you are correct.
The land on the leeward side of the mountain receives air with
the least amount of moisture, making it hotter.
The correct answer is G.
The air is drier at Y than at X. There is more moisture in the air at point X,
on the top of the mountain. All of the moisture will be lost on the
mountain, making the air at Y drier.