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How are Clouds Born?
What type of air is the least
dense?
 Warm air is less dense than cold air.
 Moist air is less dense than dry air.
 The least dense air of all would be air that is
__________ and __________
What type of air is the least
dense?
 Warm air is less dense than cold air.
 Moist air is less dense than dry air.
 The least dense air of all would be air that is
warm and moist.
How does density affect air
movement?
 Cold, dry air is more dense and will ____.
 Warm, moist air is less dense and will ____
How does density affect air
movement?
 Cold, dry air is more dense and will sink.
 Warm, moist air is less dense and will rise.
What about temperature?
 As we rise up through the troposphere
temperature will _______.
 Therefore a column of warm moist air rising will
get colder as it gains altitude.
 This column of air will also expand due to the fact
that air molecules at higher altitudes are more
spread apart (less influence by gravity).
 Depending on the Relative Humidity of the air it
could eventually cool until it reaches _________
Temperature.
What about temperature?
 As we rise up through the troposphere
temperature will decrease.
 Therefore a column of warm moist air rising will
get colder as it gains altitude.
 This column of air will also expand due to the fact
that air molecules at higher altitudes are more
spread apart (less influence by gravity).
 Depending on the Relative Humidity of the air it
could eventually cool until it reaches dewpoint
Temperature.
Do the Dew!!
 At dewpoint the air is ________ and can no
longer hold more water vapor.
 If ________ ________ are present, tiny
water droplets will condense on them to
form a cloud.
 Once the water droplets grow in size and
mass, they can drop to the earth as
precipitation.
Do the Dew!!
 At dewpoint the air is saturated and can no
longer hold more water vapor.
 If condensation nuclei are present, tiny
water droplets will condense on them to
form a cloud.
 Once the water droplets grow in size and
mass, they can drop to the earth as
precipitation.
And that’s how clouds are born!
Do Now
 What is the Dew Point Temperature if the air
temperature is 8 ˚ and the Relative Humidity
is 51%?
 Answer: -2 ˚
Do Now
 What is the Relative Humidity if The dry bulb
is 16 ˚ and the dew point is 4 ˚?
 Answer: 45%
Do Now
 What is the Relative humidity of the
following air mass? Dry Bulb=26˚;
Dew Point=11 ˚?
 Answer: 39%
Do Now
 What is the Relative humidity of the
following air mass? Dry Bulb=26˚;
Dew Point=18 ˚?
 Answer: 64%
Do Now
 What is the Relative humidity of the
following air mass? Dry Bulb=26˚;
Dew Point=25 ˚?
 Answer: 92%
Do Now
 What happens to relative humidity as the
difference between air temperature and dew
point temperature gets smaller?
 Answer: Relative Humidity increases.
Do Now
 What happens to the difference between air
temperature and dew point temperature as
air descends? (Use the cloud base altitude
chart)
 Answer: It increases.
Do Now
 Is a descending air mass becoming more or
less humid?
 Answer: Less Humid.
Orographic Effect
Orographic Effect
 A mountain can force air to rise.
 As the air rises it cools and expands.
 When the air reaches dew point temperature
clouds form ( if condensation nuclei are
present).
 As the air moves past the mountain it will
sink and become dry due to an increase in
temperature.
Orographic Effect
 The moist side of the mountain is called the
windward side, and will have a lot of
precipitation throughout the year.
 The dry side of the mountain is called the
leeward side and will often be the site of
deserts.