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Surface-based temperature inversion

Remote Pilot (Part 107) practice question 13 of 25 on Weather / Effects on Performance. ACS element UA.III.B.K1c · difficulty: standard. Want to answer it in a timed quiz? Use the Remote Pilot (Part 107) practice mode.

Question bank updated 2026-09-22

QUESTIONA remote pilot plans an early-morning flight after a clear, cool, calm night. Which atmospheric condition is most likely to exist near the surface?

  1. AStrong convective turbulence caused by rapid surface heating overnight
  2. BA shallow layer of smooth, stable air with a temperature inversion
  3. CA deep layer of unstable air with cumuliform clouds forming
Show the answer and explanation

Correct answer: B. A shallow layer of smooth, stable air with a temperature inversion

  • A — incorrect The ground cools rather than heats overnight, and cooling of the lowest layer suppresses convection instead of producing it.
  • B — correct Surface-based inversions form on clear, cool nights when the ground cools the air within a few hundred feet of the surface, creating a shallow layer of smooth, stable air.
  • C — incorrect Cooler air beneath warmer air is stable; unstable air and cumuliform clouds are associated with warm, moist conditions.

BACKGROUND

Normally the temperature of the air decreases as it rises and expands. When the temperature instead rises with altitude, a temperature inversion exists. Inversion layers are commonly shallow layers of smooth, stable air close to the ground, and the air at the top of the layer acts as a lid that traps weather and pollutants below. Surface-based inversions occur on clear, cool nights when the air close to the ground is cooled by the ground itself, so the air within a few hundred feet of the surface becomes cooler than the air above it. If humidity is high, fog, haze or smoke can reduce visibility within the inversion.

STUDY TIP

Associate "clear, cool, calm night" with a surface inversion, and expect smooth air but possibly poor visibility in the morning.

KEY POINTS

  • An inversion exists when temperature rises with altitude.
  • Surface inversions form on clear, cool nights as the ground cools the lowest air.
  • Inversion layers are shallow, smooth and stable but can trap fog, haze and smoke.

SOURCES

  • remote_pilot_study_guide.txt ch3b "Inversion"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on 14 CFR part 107, 14 CFR part 89, and the FAA Remote Pilot – Small UAS Study Guide (FAA-G-8082-22). Regulations and handbooks are revised; confirm details against the current edition.