Visibility & Fog
Visibility & Fog is a core knowledge area on the Aviation Weather FAA written exam. This hub collects our 6 in-depth, ACS-aligned visibility & fog articles — each written in plain English and grounded in the official FAA handbooks. Work through them below, then drill the topic with practice questions.
Advection Fog and Sea Fog: How Moving Air Creates Low Visibility
Advection fog forms when moist air moves over a colder surface, cooling below its dewpoint; at sea this becomes sea fog. Unlike radiation fog, it can strike any time of day, persist for days, and intensify with winds up to about 15 knots.
Fog Formation Basics: Cooling, Saturation, and Condensation Nuclei
Fog forms when air cools to its dewpoint or gains moisture until saturated, creating suspended water droplets at the surface that reduce visibility below 5/8 statute mile. Understanding the six fog types and their formation mechanisms is essential for safe flight planning.
Upslope, Steam, and Frontal Fog: Lesser-Known Fog Types
Upslope, frontal, and steam fog form through moisture-addition or orographic cooling rather than simple radiative cooling — understanding each type's trigger, behavior, and hazards is essential for safe flight planning.
Haze, Smoke, and Mist: Non-Fog Visibility Restrictions
Haze, smoke, mist, and other non-fog obscurants can severely reduce visibility for pilots. Understanding how each forms, disperses, and differs from fog is essential for safe flight planning and in-flight decision-making.
Blowing Snow, Dust Storms, Haboobs, and Volcanic Ash
Blowing snow, dust storms, haboobs, and volcanic ash are severe visibility hazards that can reduce horizontal and slant-range visibility to zero with little warning, threatening aircraft operations from ground level to the upper atmosphere.
Freezing Fog and Ice Fog Hazards in Cold Weather
Freezing fog and ice fog create invisible icing hazards on the ground and in flight; understanding how supercooled droplets and ice crystals behave in sub-freezing conditions is critical for safe cold-weather operations.
More Aviation Weather subjects
Articles are original summaries grounded in the public-domain FAA handbooks and cite their source. ACS-aligned study aids — not a substitute for the official handbooks or regulations.