SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/aero-atmosphere-water-vapor

Air holds only zero to about 5 percent water vapor. What does that small amount do?

It causes major changes in the weather.

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  1. Almost nothing, it is too small to matter
  2. It drives big changes in the weather ✔
  3. It makes the sky look blue

Why: Water vapor is a tiny part of the air, from zero to about 5 percent. But it forms clouds, rain, fog and storms, so it is behind most of our weather.

Huh, didn't know that: Water vapor is an invisible gas; clouds are tiny liquid drops or ice, not vapor.

The dad joke
Why did the water vapor feel important? It made all the weather decisions.
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References

Answer: It drives big changes in the weather. Water vapor is a tiny part of the air, from zero to about 5 percent. But it forms clouds, rain, fog and storms, so it is behind most of our weather.

  1. FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 12 Weather Theory www.faa.gov/regulations_policies/handbooks_manuals/aviation/faa-h-8083-25c.pdf
    This small amount of water vapor is responsible for major changes in the weather.
    Checked 2026-10-10.

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