Air Masses & Frontal Systems

Temperature/Dewpoint and Clouds

Pilots should be able to anticipate marginal weather conditions, so they can either avoid or expect it. Temperature and dewpoint spread, as well as atmospheric stability, have major influence on the type of weather conditions that will form.

Lesson Notes

Visible moisture (clouds, fog, mist) only forms when temperature and dew-point are very close. Another way to say this is that visible moisture forms when the air is saturated.

Rising air expands and cools, which often causes the air to become saturated, forming clouds. The shape of clouds can tell us about the stability of the atmosphere. Unstable air is rising quickly, creating “poofy” clouds with substantial vertical development. Stable air creates relatively flat clouds with far less vertical development.

A narrow temperature/dew point spread can exist without visible moisture, but in such a circumstance, a slight disturbing of the air can cause the air to quickly saturate and form visible moisture. One such example is cool, moist fields in the early morning.

Additional Resources

• Weather Overview Handout
• Weather Symbols Handout

Flashcard Questions

• The shape of clouds is largely dependent on what?
• What kind of clouds are formed from a stable atmosphere?
• What kind of clouds are formed from an unstable atmosphere?
• What is dewpoint?
• What often happens with a close temperature and dewpoint spread?
• What does the suffix “nimbus” mean in relation to clouds?
• The temperature lapse rate, normally 2°C/1000 feet, is 5°C per 1,000 feet up to 4,000 feet. Is this a stable or unstable atmosphere.
• You are flying into a valley and notice a lot of smog and poor visibility down low. The weather clears around 2,000 feet. Is this indicative of a stable or unstable atmosphere?
• As you approach your local airport, you see small puffy clouds. If you were to fly through one, what would you expect?
• Your friend remarks to you that to avoid turbulence on warm summer days, you should avoid flying directly under clouds. Is this reasonable advice? Why or why not?