Fog Flashcards
(12 cards)
Fog is…
Just a low level cloud.
What are the 5 main types of fog?
Radiation
Advection
Upslope
Evaporation
Ice
For each of the types of fog to form, three conditions must be present in the atmosphere:
Particles in the air for moisture to attach itself to
Air must have enough water in it
Low winds
Radiation or Ground Fog
Most prevalent in the cooler nights of the fall and winter months. The situation most conducive to radiation fog is warm, moist air, over low flatland areas on clear and calm nights.
Advection Fog
Unlike radiation fog, advection fog can occur when it is windy. The word advection means a horizontal movement of air. Fog from air that moves horizontally over an area. Occurs when warmer and moister air travels via winds over an area that is cooler and dryer. As the warmer and moister air moves into the region of cooler air, it cools and the moisture condenses to form fog. Once the wind reaches about 15 kts, the advection fog is lifted from the surface into low-level stratus clouds.
Where is advection fog likely to be seen?
Near the coast. It can occur from winds blowing inland and pushing moist air over land that is cooler than the water.
Upslope Fog
Forms when warmer, moister, and stable air is forced up sloping terrain to areas of cooler air. Only occurs when air is pushed up sloping terrain via winds. Low visibility from upslope fog can occur a considerable distance away from the peak or slope of the terrain.
Two Types of Evaporation Fog
Steam fog and frontal fog
Steam Fog
When warm water from a lake or ocean evaporates into the cool air above. When enough water evaporates, it saturates the air above it and fog is formed. A pilot should be on alert because of the rising most air, and for freezing conditions from the moisture in the cool air.
Frontal fog
Occurs in frontal zones when rain from warm air masses falls into cooler and dryer air below such that the raindrops are evaporated into water vapor. If it continues to rain, the cool air continues to add water vapor until it becomes saturated and the water vapor condenses once again into fog.
Ice Fog
Fog that consists of frozen ice crystals rather than water. It occurs only in areas where it is cold enough for water molecules within the air to freeze. Usually, water droplets exist in liquid form unless they have a surface to freeze onto. But, if the temperature is cold enough, (-10 C or lower) the droplets can freeze suspended in the air.
Industrial Fog
It is common in industrial areas and cities for fog to form due to the abundance of condensation nuclei.
