Describes three ways that clouds are formed. I placed a short video clip in this slide show and would like to have someone confirm that it plays. If anyone downloads this show, pleas let me know if the convection video plays as you go through the show.

1. How Warm Moist Air is Lifted to
Form Cloudsis Lifted to
How Warm Moist Air
Form Clouds
By Moira Whitehouse PhD
Free clip art http://www.webweaver.nu/clipart/

2. Clouds form when warm moist air is lifted
and cooled. Previously we said that this
lifting action for the water cycle was
provided by convection. Here we will
look at all three ways that air is lifted
and cooled to form clouds:
Convection
Mountain lifting
Air Mass movement

3. We really need to understand two things
for this “cloud making” lesson to make
sense.
First, the temperature of the air goes down
as the elevation gets higher. Roughly, for
every 1000 feet we go up the temperature
gets about 2 degrees F cooler.
Second, the temperature of the air
determines how much water vapor
(molecules of water in the gaseous form) the
air can hold. Warmer air holds more water.

4. 1. Convection
In cold air the molecules are closer
together and the air is therefore, more
dense and heavier than warm air.
Because it is heavier, gravity pulls
harder on cold air which then forces
the lighter warm air up and out of its
way. As a result, the warmer air is
pushed up (lifted) into cooler zones
above the surface.

5. Following is a simple demonstration of
convection where a candle is used to heat
the air and a piece of burning rope is used
to show the air’s movement. Notice that
air over the candle rises and is replaced by
cool air coming down the other chimney.
Note: There is a short video on the next slide after the still shot
(Quicktime may be required to view the video).

6. Quick time

7. In our world, the Sun’s heat replaces the
candle, heating the ground which heats the
warm moist air allowing it to
be pushed up by the
cooler air.
As the warm air goes up
it gets cooled. Cool air
cannot hold as much
water vapor as warm air.
As the warm moist air is
cooled, the vapor changes to
tiny droplets of liquid, the stuff of clouds.

8. 2. Mountain lifting
When warm moist air meets a
mountain, it is pushed upward into
cooler temperatures by the slope of the
mountain itself. As this warm, moist air
moves up the mountain, it is cooled and
cannot hold as much water vapor. Once
again, the vapor changes into tiny
droplets; exactly what is needed to make
a cloud.

9. As wind or air mass movement pushes this
warm moist air toward the mountain, the
slope of the
mountain forces
it up into higher
cooler air.
In this cooler environment, the air just
can’t hold as much water vapor, and
clouds are formed as the vapor changes to
liquid droplets.

10. 3. Air Mass movement
Clouds formed because of air mass
lifting are pretty much like clouds
formed by mountains, except that the
lifting is forced by another mass of air
instead of the mountain.
Air mass lifting can occur with both
warm and cold front movement but it
is always the warm air that gets lifted.

11. When a cool air mass moves into a mass of
warm moist air, the mass of warm air is
quickly forced up and thunderclouds
develop. Thunderstorms often occur.

12. When a warm air mass moves into a mass
of cold air, it slides over top of the cold air,
is cooled and stratus clouds form. A
gentler longer rain often follows.

13. In order for these clouds to form, water
vapor had be lifted up into the colder
atmosphere.
Can you remember the three ways they
might have been lifted?