Types of Fog in Aviation

Introduction

• Speaker: Greg, FAA flight instructor, lead instructor at Pilot Institute.
• Topic: Understanding the seven types of fog for pilots.
• Purpose: To help avoid visibility issues caused by fog during flights.

What is Fog?

• Definition: Fog is a low-lying cloud formed by tiny water droplets near the Earth's surface.
• Formation: Occurs when air temperature reaches the dew point, causing water vapor to condense into visible droplets.
• Impact: Reduces visibility, affecting visual flight operations.

Difference Between Fog and Mist

• Visibility Criteria:
  • Fog: Visibility less than 5/8 statute mile.
  • Mist: Visibility greater than 5/8 statute mile.

Classification of Fog Types

• Classify fog based on how they form.

1. Radiation Fog

• Formation: At night, when surface and air cool.
• Conditions Required:
  • Clear sky: Allows maximum cooling.
  • Calm winds: Ensures uninterrupted cooling.
  • Long nights: Found in winter, allows prolonged cooling.
• Characteristics:
  • Known as ground fog if < 20 ft thick.
  • Dissipates after sunrise as ground warms.
• Common Locations: Found in high-pressure systems.

2. Advection Fog

• Formation: Warm, moist air moves over cooler ground or water.
• Characteristics:
  • Shallow and often with temperature inversion.
  • Can form with strong winds and cloud cover.

3. Upslope Fog

• Formation: Moist air rises over terrain, cooling adiabatically.
• Characteristics:
  • Common at high elevations, can extend into valleys.
  • Forms in high wind conditions due to increased lift and cooling.

4. Steam Fog (Evaporation Fog)

• Formation: Cold air moves over warm water, causing evaporation.
• Characteristics:
  • Wispy tendrils rising like steam from water surfaces.
  • Common over lakes, rivers, and reservoirs.
  • Occurs in early fall or late spring.

5. Freezing Fog

• Formation: In saturated air with surface temperatures below freezing.
• Characteristics:
  • Contains supercooled water droplets.
  • Common in cold regions, valleys, and areas with stagnant cold air.
  • Forms rime ice upon impact.

6. Ice Fog

• Formation: In extremely cold conditions.
• Characteristics:
  • Composed of tiny ice crystals.
  • Occurs well below 32°F (0°C).

7. Frontal Fog

• Formation: During warm/cold front passage.
• Characteristics:
  • Prefrontal fog with warm fronts, postfrontal with cold fronts.
  • Dissipates after front passes.

8. Precipitation Fog

• Formation: Rain falls through cold, dry air, increasing moisture and dew point.
• Association: Often with fronts, especially slow-moving cold fronts.

Conclusion

• Significance for Pilots: Fog significantly impacts VFR (Visual Flight Rules) operations.
• Advantage of IFR (Instrument Flight Rules): Less affected by fog.

Additional Resources

• Video Recommendation: Check out an uncut IFR flight video for more insights.