IMC, ceilings and visibility

What instrument weather actually is, and how ceiling and visibility are measured and reported.

14 min read · IFR weather

After this lesson you can

  • Identify the cloud families and explain which ones threaten icing or turbulence.
  • Read a cold front or warm front weather sequence and predict how ceiling and visibility will change as it passes.
  • State precisely what "ceiling" means and which cloud layers define it.
  • Distinguish flight visibility, prevailing visibility, tower visibility, and RVR, and know which one 14 CFR 91.175(c) is built on.

Two numbers -- a ceiling and a visibility -- decide whether an approach can be flown to landing. They sound simple, but "visibility" alone hides at least four different measurements, taken by different instruments or different people, and only one of them is the one the regulation actually asks about. Confusing them costs an approach that was legal, or worse, continues one that was not.

This lesson builds the vocabulary the rest of the module leans on: the cloud families that produce icing and turbulence, the fronts that move ceiling and visibility around, and the precise definitions -- ceiling, flight visibility, RVR -- that turn a METAR into a landing decision.

The rest of this lesson

  1. 1.The cloud families
  2. 2.Fronts move the numbers
  3. 3.Ceiling, precisely
  4. 4.Four different measurements, one word
  5. 5.Runway Visual Range
  6. 6.Descending below DA/DH or MDA: 91.175(c)
  7. 7.When fog is the story

These 7 sections, their figures, the checks along the way and the end-of-lesson quiz come with the IFR track. Paid once, yours for good.

See what the IFR track costsEvery module 1 is free to read, no account, no card.

Key terms

Try to recall each definition before turning the card.