This activity relates cloud and sky observations to weather changes.

What types of clouds make rain or snow?

Think about a glass of ice water sitting outside on a hot, humid day. What forms on the outside of the glass of ice water?

Temperature is the major factor affecting the amount of invisible moisture air can hold at any given time. Cooler air cannot hold as much water in the gaseous form as warmer air. As the air cools around the glass, the water vapor in air changes from a gas to a liquid to form water droplets on the side of the glass. This change of the water from a vapor to liquid water is called condensation.

This is not unlike what happens in clouds. Clouds form when warm, moist air rises and cools. For clouds to form, the water vapor must have something to condense around. There are all sorts of very small (microscopic) particles in the air like dust, soot, pollen, bits of rock, salt from the sea, and smoke from car exhaust or factories. What we see as fog or clouds is tiny droplets of water that have condensed onto these particles. Clouds may look solid at a distance, but up close they are just like fog.

• temperature sensor
• 1 pair of scissors per student group
• 1 small convex mirror per student group [51 mm (2 inch) – 95 mm (3.75 inch) diameter] (easily found in automotive section of discount stores)
• masking tape (if convex mirror is not a stick-on)
• Cloud Flow Chart
• Cloud Detective Wheel
• paper and pencil (for outside recording of clouds and wind direction)
• 1 pair of scissors per student group
• black permanent marker
• white poster board [18 mm (7 inch) x 28 mm (11 inch)]
• paper fastener (often called a brad)
• 1 compass per student group (optional)

Water in nature is always moving. It rises up to form clouds and then comes down again in different forms of precipitation. How many different forms of precipitation can you name? List the forms below.

1. High altitude winds affect cloud movements that bring changes in weather. The direction of these winds can be very important. High altitude winds do not necessarily blow in the same direction as ground winds. Can you think of some reasons why this might be true?
2. At higher altitudes, winds can move considerably faster and in a definite direction. A convex mirror marked
with the points on a compass (i.e., N, NE, E, SE, S, SW, W, NW) helps you safely view clouds and indicates
the direction of the cloud movement. This type of device is easy to make. Obtain a round convex mirror.
Notice that the mirror is not flat. This will help you see clouds across the full sky.
3, Place and attach the convex mirror in the center of a piece of poster board. Most mirrors of this type have adhesive on the back so they just stick on. If there is no adhesive on the back of the mirror, use masking tape to attach the mirror to the center of the poster board.

6. Mark the points on the poster board as shown below with a permanent marker.
7. Locate a piece of flat level ground outside that is not blocked by a tree or building. Once you have found your location either use a compass or ask your teacher which way is north. Place your convex mirror on the ground with N facing north.
8. Look in the mirror and follow the path of a cloud as it passes across the circle and past the edge of the mirror’s surface. What direction was the cloud moving?
9. Draw a picture below of the cloud that you are tracking.
10. The point at which the cloud begins its journey across the mirror indicates the high altitude (level) wind direction. For example, if clouds are moving toward the east, the wind is coming from the west. What direction was the wind moving as you observed your cloud?

11. There are many different types of clouds. Observing the shape, color, and altitude of clouds can sometimes tell us about what the weather will be like in the hours and days ahead. Let’s look at the different ways to classify clouds.

Shape: There are two different shapes or forms of clouds. They are either “heaped” (cumulus) or “spread sheeted” (stratus).

The dense, huge masses of varying heights are called cumulus clouds.

Cumulus
http://commons.wikimedia.org/wiki/Image:Bluesky2.jpg

The low, horizontal sheets of layered, lifted fog are called stratus clouds.

Stratus
http://commons.wikimedia.org/wiki/Image:Stratus.jpg

Clouds that are both heaped and spread out in layers are called stratocumulus clouds because they’re a bit like stratus and a bit like cumulus clouds.

Stratocumulus
http://commons.wikimedia.org/wiki/Image:Stratocumulus-cylinders.jpg

Color: When the color changes from a fluffy white to a dark cloud, the word nimbus is added to the beginning or ending of the cloud form. For example, a dark cumulus cloud with a dark base that is threatening to rain or hail is called a cumulonimbus cloud.

Cumulonimbus
http://commons.wikimedia.org/wiki/Image:Big_Cumulonimbus.JPG

A dark gray horizontal stratus cloud that is threatening to snow, rain, or drizzle is called a nimbostratus cloud.

Nimbostratus
http://commons.wikimedia.org/wiki/Image:Nimbostratus_praecipitatio.JPG

Height: The altitude above the ground can also describe clouds. Usually clouds are classified as low, medium, or high. Towering layered clouds that may extend to over 20,000 meters in height form a separate category called vertical clouds. Vertical clouds that have strong updrafts of air are associated with sometimes dangerous precipitation, winds, storms, and even tornadoes. There can be very strong rain and hail from these clouds.

Low: Clouds that range in height from 0 to 2000 meters are classified as low clouds. When many cumulus clouds appear in a layer over a large area of the sky these clouds are called stratocumulus. When the prefix strato- is used with the word cumulus it means a layer of cumulus clouds.

Stratocumulus
http://commons.wikimedia.org/wiki/Image:Large_Stratocumulus.JPG

Medium: Clouds that range in height from 2000 to 5000 meters are classified as medium clouds. Often the prefix alto- is used to indicate a specific medium height cloud. Altocumulus clouds often show up in regular patterns of rolls or puffs.

Altocumulus
http://commons.wikimedia.org/wiki/Image:Close_Altocumulus_in_front_of_Cs.JPG

High: Clouds whose bases are above 5000 meters are classified as high clouds. Often the prefix cirro- is used to indicate a specific high cloud height. Cirrus clouds are high level clouds that develop in filaments or wispy patches. Cirrocumulus clouds have a spotty appearance created by the many small patches. All of these clouds are so high and the air so cold that when water vapor condenses, it forms tiny ice crystals instead of water droplets.

Cirrus
http://commons.wikimedia.org/wiki/Image:Cirrus.jpg

Cirrocumulus
http://commons.wikimedia.org/wiki/Image:Cirrocumulus_to_Altocumulus.JPG

Contrails are clouds created by water vapor condensing into ice crystals on the small particles from the exhaust of planes that fly at high altitudes.

Contrails
http://commons.wikimedia.org/wiki/Image:Sfc.contrail.1.26.01.JPG

12. Click on this Cloud Flow Chart link to download and print a cloud map. With your group, discuss the various classifications of clouds. Think about different types of clouds that occur during different weather conditions. Which types of clouds are present during stormy weather?

13. Obtain the paper with the two parts of the Cloud Detective Wheel from your teacher.

14. Follow the directions on the page to cut out and connect your Cloud Detective wheel. Cut out the two discs.

15. Cut out the dark areas on the top disc where it reads “Cut Out.”

16. Make a small hole on each disc where the red stars are positioned.

17. Use a paper fastener (brad) to attach the bottom to the top. Make sure that the wheel can rotate easily, showing you different cloud types and their descriptions.

18. Notice the symbols that are used for each cloud. Review the above the descriptions of clouds with your group using your Cloud Flow Chart and be prepared to identify clouds.

19. Review your drawing of a cloud using the convex mirror. Use your Cloud Detective wheel to identify the type of cloud and choose the proper symbol.

20. Take your convex mirror outside with your Cloud Detective wheel three days in a row. Record on paper your findings.

21. Use the temperature sensor to record the air temperature.

22. Use the draw program to complete a journal below. Please include the date, observable weather conditions (for example, rainy, foggy, hazy, etc.), the type of clouds (sketch the symbol), the wind direction and air temperature for the day.

23. Continue journaling for four days at about the same time each day (weather permitting).

24. Based on your Cloud Journal, was there a change in weather conditions? Be prepared to share your observations with the class.

1. Why are high altitude winds important for weather forecasting?
2. If a cloud passes from northeast to southwest, which direction is the high altitude wind coming from?
3. What are low-leveled heaped clouds called?
4. What types of clouds are so high that when water vapor condenses, it forms tiny ice crystals?

Were there days when multiple types of clouds are present? If so, how did this relate to changing weather conditions? Be prepared to share your answers with the class.

• Observe and paint the color of the sky with watercolors to add further descriptions to an additional three-day cloud journal. How does the color of the sky relate to weather conditions?

• Use a digital camera to capture the cloud types to add further descriptions to an additional three-day cloud journal. Share your pictures of the clouds with other groups to check if the correct type of clouds were identified in your journal.