01
Cumulus
Updraft
The cloud grows vertically. The FAA identifies the updraft as the defining feature of this stage.
Part 107 weather
Stable vs unstable air for Part 107
Stable air resists vertical motion. Unstable air lets it build. That one distinction explains the cloud shape, precipitation, turbulence, and visibility clues the exam combines.
WX · STABILITYShort answer
Layered points to stable. Vertical points to unstable.
Stable air suppresses rising parcels, so moisture tends to spread into layers. Expect stratiform clouds or fog, smoother air, steady precipitation, and visibility reduced by haze or smoke.
Unstable air supports rising motion, so clouds build upward. Expect cumulus, showers, turbulence, and usually better visibility between precipitation or blowing obstructions.
FAA comparison
Four clues, read together
The exam may give you one clue and ask for another. Use the whole pattern instead of memorizing a single word.
- Clouds
Stable air
Stratiform clouds and fog
Unstable air
Cumuliform clouds
- Precipitation
Stable air
Continuous
Unstable air
Showery
- Ride
Stable air
Smooth air
Unstable air
Rough air and turbulence
- Visibility
Stable air
Fair to poor in haze and smoke
Unstable air
Generally good, except in blowing obstructions
What the atmosphere is doing
Stability is about vertical motion, not whether the sky looks calm.
Stable: displaced air tends to return toward its original level. Vertical mixing is limited.
Unstable: rising air keeps moving upward. Vertical development and turbulence become more likely.
Thunderstorm lifecycle
The current tells you the stage
A thunderstorm cell moves through three stages. The transition is gradual, and a cluster may contain cells in different stages at the same time.
02
Mature
Updraft and downdraft
Precipitation reaches the surface and both currents coexist. Turbulence and other hazards are strongest here.
03
Dissipating
Downdraft
Descending air dominates and the cell weakens, although the remaining conditions are not a reason to fly near it.
Apply the pattern
Three ways the exam can ask it
These are original Drone Authority questions mapped to the FAA knowledge areas. Pick an answer for yourself, then reveal the explanation.
Worked question 1
Stable air is commonly associated with:
- APoor surface visibility from trapped haze, smoke, or moisture
- BStrong vertical currents, towering cumulus, and showery precipitation
- CGood surface visibility because pollutants mix vertically
- DFrequent abrupt wind shifts caused by convective cells
Show the answer and reasoningAnswer and reasoning
A. Poor surface visibility from trapped haze, smoke, or moisture
Stable air is often smooth, but it can trap haze, smoke, or moisture near the surface, reducing visibility.
Worked question 2
Unstable air is more commonly associated with:
- ATurbulence, good visibility, cumulus clouds, and showery precipitation
- BSmooth air, poor visibility, and widespread stratiform clouds
- CA surface inversion with smoke and haze trapped near the ground
- DSteady precipitation from layered clouds with little turbulence
Show the answer and reasoningAnswer and reasoning
A. Turbulence, good visibility, cumulus clouds, and showery precipitation
Unstable air favors vertical motion. It is often bumpier, with better visibility, cumulus clouds, and showery precipitation.
Worked question 3
A cold front is most likely to bring which concern for small UAS operations?
- AWidespread steady precipitation with smooth, stable air
- BGusty winds, turbulence, and possible thunderstorms
- CA gradual warming trend with little wind shift
- DPersistent fog with no turbulence or gusts
Show the answer and reasoningAnswer and reasoning
B. Gusty winds, turbulence, and possible thunderstorms
Cold fronts often bring abrupt weather changes, gusty winds, turbulence, precipitation, and thunderstorms.
Stable and unstable air questions
- Is stable air always safer for a drone?
- No. Stable air is usually smoother, but it can trap haze, smoke, fog, and moisture near the surface. That can reduce visibility below legal or practical flight limits.
- Does unstable air always mean a thunderstorm?
- No. Unstable air favors vertical motion, cumuliform clouds, showery precipitation, and turbulence. A thunderstorm is one possible result when enough moisture and lift are also present.
- Which cloud shape is the fastest exam clue?
- Layered or stratiform clouds point toward stable air. Puffy clouds with strong vertical development point toward unstable air.
- Which thunderstorm stage is most hazardous?
- The mature stage. Updrafts and downdrafts exist together, precipitation reaches the surface, and thunderstorm hazards reach their greatest intensity.
Primary source
FAA Remote Pilot Small Unmanned Aircraft Systems Study GuideEducational reference only. For an actual flight, use current weather observations and forecasts, aircraft limitations, and your own conservative go or no-go decision.