Overview

Clouds are divided into four basic forms (cirro-form, strato-form, cumulo-form and nimbo-form) at three basic levels (low, middle and high) in the atmosphere. Many locations may experience all of these different types of clouds daily. The students will become better observers of the sky by recording the different cloud types at various times daily.

Procedure

1. 

   Have the students cut out their disc and each of the eleven cloud images.
2. Glue or tape cloud images into their respective locations on the disc by matching the cloud abbreviation. (The clouds are grouped into low, middle and high clouds.)
3. Hold the disc up into the sky and peer through the hole at the clouds.
4. As best as possible, match each cloud type. If there is more than one type of cloud for any particular level (low, middle, high) the cloud that has the greatest sky coverage is the predominant cloud for that level. The only exception is the low cloud Cumulonimbus (Cb). If ANY Cb is observed, it is the predominant cloud type regardless of size or percentage of sky cover of any other low cloud.
5. Record the predominant cloud code onto the Cloud Observation Form.
   • If there are no clouds at any particular level then enter a zero (0) to indicate the absence of clouds at that level.
   • If the sky is overcast at any particular level and there is no ability to see clouds above the overcast, enter a dash (-) for any level(s) ABOVE the overcast level.
6. Have the students repeat the cloud observation procedure again at home this evening and to make their observations as close to the same time as possible each day.
7. Repeat for five days.

Discussion

Identifying clouds can be difficult at first. Have the students make their best effort in identifying the predominant cloud(s). Here are some helpful hints:

• Low level clouds usually move faster, and in a different direction, when compared to mid- and high-level clouds.
• When the sky is covered mostly by low level clouds, look through any gaps in the low-level clouds to determine if there are any mid and high level clouds above that lowest layer.
• After sunrise, fog often lifts from the ground and becomes a stratus (St) cloud.
• An overcast sky of stratus (St) or nimbostratus (Ns) usually gray and featureless. The difference between the two can be discerned by the type of precipitation (if any). If it is raining, then the cloud is nimbostratus. If NOT raining (it is drizzling/mist or there is no precipitation) then the cloud is stratus. In either case, weather conditions for nimbostratus and stratus will usually mean this will be the only type of cloud seen.
• Altocumulus (Ac) can be opaque or semi-transparent (as seen in the two examples on the disc).
• Use the 1-2-3 finger rule to discern the difference between stratocumulus (Sc), altocumulus, and cirrocumulus (Cc).
  • If the individual cloud element is smaller than the width of one finger, at arm's length, then the cloud is cirrocumulus.
  • If the individual cloud element is larger than the width of one finger, but smaller than the width of two fingers at arm's length, then the cloud is altocumulus.
  • If the individual cloud element is larger than the width of two fingers, at arm's length, then the cloud is stratocumulus.
• Cumulonimbus (Cb) clouds are large, low clouds that grow very tall. Hearing thunder or seeing lightning indicates the cloud type as a cumulonimbus. If you hear thunder, you must get indoors immediately as you are close enough to be stuck by lightning.

Discuss any changes in the cloud type between the daytime observation at school and the evening observation at home. Discuss how the types of clouds change during the week, especially if a front passes your location. Discuss how we can look at the clouds to help forecast the weather. The Cloud Cycle wheel shows how the types of clouds change before and after fronts.