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3.3 Clouds, Visibility, and Fog

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FAA Part 107 Remote Pilot Certificate Exam

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1 Introduction to the FAA Part 107 Remote Pilot Certificate

FAA Part 107 Exam Overview Study Strategy and Test-Taking Tips

2 1. Regulations (14 CFR Part 107)

1.1 Applicability and Definitions (Subpart A) 1.2 Remote Pilot Certification (Subpart C) 1.3 Operating Rules Overview (Subpart B) 1.4 Registration and Marking Requirements 1.5 Remote Identification (Part 89) 1.6 Operations Over People (Subpart D) 1.7 Night Operations and Civil Twilight 1.8 Waivers and Authorizations (Subpart E) 1.9 Accident Reporting and Recordkeeping 1.10 Preflight Familiarization and Actions

3 2. Airspace Classification & Requirements

2.1 National Airspace System Overview 2.2 Class B Airspace 2.3 Class C and Class D Airspace 2.4 Class E and Class G Airspace 2.5 Reading Sectional Charts 2.6 LAANC and Airspace Authorization 2.7 TFRs and NOTAMs 2.8 Latitude, Longitude, and Navigation

4 3. Weather

3.1 Weather Theory and Atmospheric Basics 3.2 Wind, Turbulence, and Wind Shear 3.3 Clouds, Visibility, and Fog 3.4 Reading METAR Reports 3.5 Reading TAF Reports 3.6 Weather Hazards for Drone Operations 3.7 Weather Information Sources

5 4. Loading and Performance

4.1 Weight, Balance, and Center of Gravity 4.2 Density Altitude and Performance 4.3 Load Factor and Maneuvering 4.4 Battery Performance and Management 4.5 Performance Calculations and Limitations

6 5. Operations

5.1 Crew Resource Management (CRM) 5.2 Aeronautical Decision Making (ADM) 5.3 Emergency Procedures 5.4 Physiological Factors Affecting Pilots 5.5 Radio Communication and Frequencies 5.6 Airport Operations and Traffic Patterns 5.7 Maintenance, Inspection, and Condition 5.8 Special Operations and Considerations 5.9 Flight Planning and Risk Mitigation 5.10 Sectional Chart Interpretation Exercises

3.3 Clouds, Visibility, and Fog

Key Takeaways Explain This Topic AI

Part 107 minimums: 3 statute miles visibility, 500 ft below clouds, 2,000 ft horizontal from clouds.

A ceiling is the lowest BKN (broken) or OVC (overcast) layer; FEW and SCT are never ceilings.

Radiation fog forms on clear, calm nights in low areas and burns off after sunrise.

Advection fog forms when warm, moist air moves over a cooler surface and can persist any time of day.

Cumulonimbus (Cb) clouds mean thunderstorms, the most hazardous cloud type for aviation.

Last updated: June 2026

  • Clouds, Ceilings, and Visibility
  • The Part 107 Weather Minimums (Memorize These)

Under 14 CFR 107.51(c) , every operation must meet both a visibility and a cloud-clearance standard, measured from the control station.

  • Requirement Value
  • Minimum flight visibility 3 statute miles (SM) from the control station
  • Below clouds 500 ft
  • Horizontal from clouds 2,000 ft

A handy memory aid is "3-cubed minus" : think 3 SM, 5(00), 2,000. If a question shows visibility under 3 SM or a ceiling that prevents 500 ft of vertical clearance, the answer is no-go .

Cloud Classification

Clouds are named by altitude and form (Latin roots: cirro = high, alto = middle, strato = layered, cumulo = heaped, nimbo = rain).

High clouds (above ~20,000 ft):

  • Cirrus (Ci) — thin, wispy ice-crystal streaks
  • Cirrocumulus (Cc) — small white ripples
  • Cirrostratus (Cs) — thin sheet causing a halo around the sun or moon

Middle clouds (~6,500-20,000 ft):

  • Altostratus (As) — gray-blue sheet over much of the sky
  • Altocumulus (Ac) — gray-white patches, larger than cirrocumulus

Low clouds (surface-6,500 ft):

  • Stratus (St) — uniform gray blanket
  • Stratocumulus (Sc) — low, lumpy gray rolls
  • Nimbostratus (Ns) — dark, steady-rain layer

Clouds of vertical development:

  • Cumulus (Cu) — puffy fair-weather clouds, flat bases
  • Towering cumulus (TCu) — tall, building rapidly, a warning sign
  • Cumulonimbus (Cb) — the thunderstorm cloud and most dangerous for flight
  • Cloud Coverage and the Definition of a Ceiling

Coverage is reported in eighths of the sky (oktas):

  • Code Meaning Coverage
  • SKC / CLR Sky clear 0/8
  • FEW Few 1/8-2/8
  • SCT Scattered 3/8-4/8
  • BKN Broken 5/8-7/8
  • OVC Overcast 8/8

A ceiling is the lowest BKN or OVC layer . FEW and SCT are never ceilings because they do not cover most of the sky.

Worked example: With FEW010 SCT020 BKN040 , the ceiling is 4,000 ft AGL (the first broken layer) — not the lower few or scattered layers.

Visibility Obstructions

  • Obstruction (code) Typical visibility Operations impact
  • Haze (HZ) 3-5+ SM Marginal — confirm 3 SM
  • Mist (BR) 5/8 to under 7 SM May limit visual line of sight
  • Fog (FG) Less than 5/8 SM No-go
  • Smoke (FU) Varies Check actual value
  • Five Types of Fog

Fog type How it forms Telltale conditions

Radiation Ground cools on a clear, calm night, chilling the air Valleys/low ground; burns off after sunrise; winds under 5 kt

  • Advection Warm, moist air moves over a cooler surface Coastlines; any time of day; needs some wind; persistent
  • Upslope Moist air pushed up a slope cools to saturation Mountainous terrain; needs upslope wind
  • Steam Cold air moves over warm water Lakes/rivers in fall and early winter; shallow
  • Precipitation-induced (frontal) Warm rain falls through cool air and evaporates Ahead of warm fronts
  • Applying the Minimums to a Real Sky

Suppose you launch under a layer reported as BKN012 (broken at 1,200 ft AGL). Part 107 caps you at 400 ft AGL, and you must stay 500 ft below clouds — so the highest you could legally fly is 1,200 − 500 = 700 ft, which is above your 400 ft ceiling anyway. The flight is legal on cloud clearance. Now drop the layer to BKN004 (400 ft). The 500-ft-below rule would force you down to roughly the surface, so the operation is a no-go : you cannot hold both 400 ft of useful altitude and 500 ft of clearance. Working the arithmetic, rather than guessing, is what the exam rewards.

Visibility is judged from the control station , not the aircraft. A reported 3 SM exactly meets the minimum; anything lower (mist at 1.5 SM, fog under 5/8 SM) is an automatic no-go regardless of how clear it looks straight up.

Why Cloud Type Matters Beyond Naming

Memorizing Latin names earns a point or two, but the operational message is what counts. Cumulonimbus equals thunderstorm and everything in Section 3.6 that goes with it. Towering cumulus is the visible warning that the atmosphere is destabilizing and a storm may be an hour away. A lowering nimbostratus or stratus deck means a falling ceiling that can clip your legal clearance fast. Watching cloud trends, not just current coverage, keeps a flight legal as conditions evolve.

Common Cloud, Visibility, and Fog Traps

FEW or SCT counted as a ceiling. Only BKN and OVC form a ceiling.

Forgetting the hundreds-of-feet conversion. OVC008 is 800 ft, not 8 ft or 8,000 ft.

Swapping fog drivers. Radiation fog needs calm ; advection fog needs wind to push warm moist air over a cool surface.

Reading visibility from the aircraft. Part 107 measures the 3 SM minimum from the control station .

The Temperature/Dew-Point Spread

The single most useful fog predictor on the exam is the temperature/dew-point spread . As an air mass cools toward its dew point, relative humidity climbs toward 100 percent; when temperature and dew point converge (a spread near 0 to 2 deg C ), the air is saturated and fog or low stratus is likely . A METAR reading 02/01 (1 deg spread) is a fog warning; 24/09 (15 deg spread) is dry, clear air. The exam often gives you a METAR and asks which condition is most likely — pick the saturated, small-spread answer for fog.

Fog Types Compared

  • Type Forms when Wind needed? Persistence
  • Radiation fog Clear, calm, cool night cools the ground No — needs calm Burns off after sunrise
  • Advection fog Warm, moist air moves over a cooler surface Yes — light wind Can last all day
  • Upslope fog Moist air pushed up rising terrain, cooling adiabatically Yes Lasts while flow continues
  • Steam/evaporation fog Cold air over warm water No Patchy, localized

For the exam: The two heavily tested types are radiation fog (clear, calm, cool night, burns off) and advection fog (warm moist air over a cool surface, needs wind, can last all day). Note that advection fog needs wind while radiation fog needs calm — a classic contrast question. A small temperature/dew-point spread on the supplied METAR is your tell that fog is imminent.