Look up at the sky and watch how the clouds change. Their shape, height and development offer clues about moisture, atmospheric stability and what the weather might do next.
Photo by Shyamal, Wikimedia Commons (CC0).
The World Meteorological Organization (WMO) groups cloud genera by the levels where they usually occur. The height ranges vary with latitude. These approximate values apply to temperate regions:
| Level | Approximate height | Examples |
|---|---|---|
| Low | Surface to 2 km | Stratus, Stratocumulus |
| Middle | 2–7 km | Altocumulus, Altostratus |
| High | 5–13 km | Cirrus, Cirrostratus |
Low clouds usually consist mainly of water droplets, although they can also contain ice crystals. A uniform sheet of stratus may produce drizzle. Stratocumulus forms banks or rolls, while cumulus grows upwards from its base.
Altocumulus appears in patches of rounded cloud elements. Altostratus forms a more extensive veil that can signal an approaching frontal system. Watch how the cloud cover develops over time before drawing conclusions from a single cloud.
Cirrus looks like fine threads or feathers. Cirrostratus spreads into a thin veil that sometimes produces a halo around the Sun or Moon. Cirrocumulus consists of small, repeating cloud elements.
High clouds can reveal moisture in the upper atmosphere. Changes in their coverage and form can also give clues to changes in the wider circulation.
Switch between total, high, middle and low cloud cover. Each layer shows the fraction of the sky the model expects clouds to cover. To identify a particular cloud type, you also need to look at its appearance.
Open the Meteorix map ↗Its base is usually low, but it grows vertically and can reach the upper troposphere.
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