Air masses and fronts

How air masses form, what happens at the boundary between two of them, and the sequence of weather each type of front brings.

14 min read · Weather

After this lesson you can

  • Describe how an air mass takes on the temperature and moisture of its source region.
  • Distinguish a warm front, a cold front, a stationary front, and an occluded front.
  • Predict the sequence of pressure, temperature, and cloud changes as a front approaches and passes.
  • Recognize a squall line and explain why it is treated as more dangerous than an ordinary line of showers.

Almost all significant, organized weather comes from the collision of two air masses that do not want to mix. Understanding what each air mass carries with it, and what happens at the boundary where they meet, lets you read a lot of weather from very little information: a single METAR trend, a falling barometer, or a shift in wind direction can tell you where a front is and what it is about to do.

This lesson builds the vocabulary for everything that follows in the module: the fronts described here are what triggers the clouds, the icing, and the thunderstorms covered in the next three lessons.

The rest of this lesson

  1. 1.What makes an air mass
  2. 2.The warm front
  3. 3.The cold front
  4. 4.Stationary and occluded fronts
  5. 5.Reading the passage of a front
  6. 6.Deciding in VFR: reading a front for a go/no-go call

These 6 sections, their figures, the checks along the way and the end-of-lesson quiz come with the PPL track. Paid once, yours for good.

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

Key terms

Try to recall each definition before turning the card.