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Fog and Aviation: Understanding Different Types of Fog

Fog is one of the most significant weather hazards in aviation. While it may look harmless from the ground, fog drastically reduces visibility, making takeoffs, landings, and even taxiing extremely challenging and sometimes unsafe. Pilots must understand how fog forms, the different types that exist, and the operational impacts it can have on flight safety.


Let’s break down the primary types of fog relevant to aviation: radiation fog, advection fog, upslope fog, steam fog, and ice fog.



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What is Fog?

In meteorology, fog is essentially a cloud that forms at or near the ground. It develops when the air becomes saturated with moisture and water vapor condenses into tiny droplets suspended in the air. For pilots, the key concern is reduced visibility, often dropping below 1 statute mile, which can create instrument flight rules (IFR) conditions and delay or prevent VFR (visual flight rules) operations.


Types of Fog in Aviation

1. Radiation Fog

  • Formation: Radiation fog forms on clear nights with calm or light winds. As the ground radiates heat into space, it cools rapidly, chilling the air close to the surface. If this cooling brings the air temperature down to the dew point, fog forms.

  • Where it’s common: Valleys, flat terrain, and airports surrounded by fields.

  • Aviation impact: It often develops overnight and may persist into the morning until the sun warms the ground enough to dissipate it. Pilots should expect early morning delays in areas prone to this type of fog.


2. Advection Fog

  • Formation: Advection fog occurs when warm, moist air moves horizontally (advects) over a cooler surface, causing condensation. Unlike radiation fog, it doesn’t depend on nighttime cooling.

  • Where it’s common: Coastal areas, particularly when warm air moves over a cold ocean current or landmass.

  • Aviation impact: Advection fog can be persistent and widespread, sometimes lasting for days, significantly impacting airport operations along coastlines.


3. Upslope Fog

  • Formation: Upslope fog forms when moist air is forced up a sloping terrain (such as a mountain or hill) and cools as it rises, reaching saturation.

  • Where it’s common: Mountainous and hilly regions where winds push moist air uphill.

  • Aviation impact: Upslope fog can cover large areas and linger, making flying in mountainous terrain especially dangerous for VFR pilots.


4. Steam Fog (Evaporation Fog)

  • Formation: Steam fog occurs when cold air moves over warmer water. The warm water evaporates into the cold air, quickly saturating it and forming fog.

  • Where it’s common: Lakes, rivers, and coastal waters during cold weather.

  • Aviation impact: Steam fog is usually patchy and localized but can still cause sudden reductions in visibility for aircraft operating near bodies of water.


5. Ice Fog

  • Formation: Ice fog develops in extremely cold temperatures (below about –30°C/–22°F). Instead of liquid water droplets, it forms from tiny ice crystals suspended in the air.

  • Where it’s common: Arctic and polar regions, or very cold inland areas.

  • Aviation impact: Ice fog severely reduces visibility and can create dangerous conditions for both pilots and ground crews. It also poses additional challenges like frost accumulation on aircraft surfaces and airport equipment.


Fog and Flight Operations

For pilots, fog means:

  • Reduced visibility: Often requiring instrument flight rules (IFR).

  • Delays and diversions: Many airports will hold or reroute flights during dense fog events.

  • Decision-making challenges: Pilots must evaluate departure and destination conditions carefully, paying close attention to forecasts of fog dissipation or persistence.


Conclusion

Fog is a common yet potentially dangerous weather phenomenon in aviation. By understanding how different types of fog form—radiation, advection, upslope, steam, and ice fog—pilots can anticipate conditions that may lead to reduced visibility. Careful preflight planning, knowledge of local geography, and weather awareness are essential tools for safely navigating foggy conditions.



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