Which fog occurs when a warm and moist underlying surface evaporates additional water vapor into the overlying air and the air mass becomes saturated?

Which fog occurs when a warm and moist underlying surface evaporates additional water vapor into the overlying air and the air mass becomes saturated?

• A. Frontal fog
• B. Evaporation/Steam fog
• C. Radiation fog
• D. Ice fog

Answer: (B)

Fog forms when air reaches its dew point, which can happen either by cooling or by adding moisture to the air. In this scenario, a warm, moist surface continuously releases water vapor into the layer of air above. As that vapor mixes with the cooler air, the humidity rises toward 100 percent. When the air becomes saturated, the vapor condenses into tiny droplets and a visible fog forms at the surface. This is evaporation (or steam) fog, often seen over a lake or warm ground when the surface keeps sending moisture upward into cooler air. Radiation fog, by contrast, forms mainly from nighttime cooling of air near the ground, without extra moisture being added from a warm surface. Frontal fog comes from evaporation of precipitation within moist air at a front, and ice fog occurs in very cold conditions where water vapor deposits as ice crystals.

Fog forms when air reaches its dew point, which can happen either by cooling or by adding moisture to the air. In this scenario, a warm, moist surface continuously releases water vapor into the layer of air above. As that vapor mixes with the cooler air, the humidity rises toward 100 percent. When the air becomes saturated, the vapor condenses into tiny droplets and a visible fog forms at the surface. This is evaporation (or steam) fog, often seen over a lake or warm ground when the surface keeps sending moisture upward into cooler air.

Radiation fog, by contrast, forms mainly from nighttime cooling of air near the ground, without extra moisture being added from a warm surface. Frontal fog comes from evaporation of precipitation within moist air at a front, and ice fog occurs in very cold conditions where water vapor deposits as ice crystals.