Download Clouds and Precipitation

Name: _________________________________Date: ________________________Period: ____
Unit 11: Meteorology
Cloud Formation and Precipitation
Your Task:
With our knowledge of humidity and dew point, we can start to understand how clouds and
precipitation form. In this activity, we are going to look at the ingredients necessary to make a cloud
and how they form.
Ingredients of Cloud Formation
Clouds are a large collection of tiny droplets of water or ice crystals. These droplets or crystals are so
small and light that they can float in air. Since most clouds are made from water droplets, the main
process involved in their formation is condensation. To have condensation, the air must be saturated.
If you have ever had a glass of cold lemonade outside on a hot day, you have seen condensation form
on the glass. You may have also noticed condensation form on the mirror in your bathroom when you
have taken a shower. In all cases, a surface is required for the water vapor to condense onto. In the
atmosphere, there are tiny particles known as condensation nuclei that provide this surface. They often
come from soil, the ocean in the form of sea salt, and the burning of vegetation and fossil fuels. These
particles are extremely small with a diameter of about 0.0002 – 0.006 mm.
Check your understanding:
1. What is the main phase change is involved with cloud formation? _______________________
2. What are the two main ingredients to form a cloud?
_________________________
_________________________
Reaching Saturation
Air can become saturated in two ways. We can add water vapor to the air, or we can cool the air down
until it reaches the dew point. There are many ways for air to be cooled to its dew point, such as
coming in contact with a colder surface or mixing with colder air.
The main way that air cools to form a cloud is by rising
into the upper troposphere. As an air parcel rises, it
experiences less pressure. The parcel will expand until the
inside pressure equals the atmospheric pressure (Patm)
outside the parcel. As the molecules of the parcel “push
out”, they use some of their internal energy. If they have
less energy, then the temperature of the air parcel
decreases. This process is known as adiabatic cooling.
Check your understanding:
1. As you go up in the troposphere, the air pressure (increases,
decreases, remains the same).
2. As you go up in the troposphere, air parcels (expand, contract).
3. As you go up in the troposphere, the temperature of an air parcel (decreases, increases,
remains the same).
Once air parcel reaches its dew point temperature, condensation will occur and the cloud will begin to
form. The altitude at which this occurs is known as the lifted condensation level. This is where the
base of the cloud will be located.
Check your understanding:
1. What is the dew point of the air parcel shown in the
diagram?
_______________________
2. What is the lifted condensation level of the air parcel
shown in the diagram?
______________
Precipitation
Precipitation includes all forms of water that fall from clouds. Common
forms of precipitation are rain, snow, sleet, and hail. In warm clouds,
precipitation forms from condensation. As they form, water droplets
within the cloud will merge. When they become too heavy they will fall
as rain. In cold clouds, precipitation forms from deposition. In these
clouds, water vapor changes directly to ice crystals like the ones shown.
Hail is associated with thunderstorm clouds. These clouds are
very tall so they contain a warm and a cold part. These types
of clouds also have a large updraft that will move water
droplets from the warm part up to the cold part of the cloud.
When these water droplets are moved up, they freeze. They
will then drop back down to the warm part of the cloud where
they become covered in water. Eventually they will move
back up to the cold part of the cloud and this new layer of
water will freeze. This cycle will repeat until the piece
becomes too heavy and falls to the ground. If you cut open a
hailstone you can see the different layers. Hail can come in
many different sizes, from the smallest marble-sized pieces to
the largest grapefruit or softball-sized pieces.
Check your understanding:
1. Rain is associated with (warm, cold) clouds while snow is associated with (warm, cold) clouds.
2. Cold clouds create precipitation through what phase change? ________________________
3. Warm clouds create precipitation through what phase change? ________________________
4. Can we have hail in the winter? Explain.