Fog is a surface-based cloud composed of either water droplets or ice-crystals.
Fog is the most frequent cause of surface visibility below 3 miles.
Fog may form by cooling the air to its dew point or by adding moisture to the air near the ground.
A small temperature dew point spread is an indication that fog can form.
There are different types of fog, and it is classified by the way it is formed.
Radiation fog also known as ground fog.
It is formed when terrestrial radiation cools the ground which then cools the air in contact with it.
When the air is cooled to its dew point or when it is within a few degrees, fog will form.
This fog will form most readily in warm moist air over low flatland areas on clear calm nights.
Advection fog alson known as sea fog.
It is formed when warm moist air moves over colder ground or water.
It can be an air mass moving inland from the coast in the winter.
Upslope fog is formed when moist stable air is cooled to its dew point as it moves uphill.
Cooling will be at the dry adiabatic lapse rate of approximately 3 degrees celsius per 1,000 feet.
