Moisture from the warm land or water evaporates into the lower layers of the cool air passing over, leading to a mixing of temperature that causes condensation and often fog formation.Īdvection fog forms when warm humid air passes over relatively cold surfaces, such as snow or frozen ground. Warmer air passing above the valley creates a temperature inversion leading to condensation of air in the valley, which can last for days in some cases.Įvaporation fog is formed when cold air passes over warmer water or warm moist land. Valley fog occurs in mountainous areas where the cold dense air is trapped by the steep sides of valleys.

This type of fog usually dissipates when the sun rises and is known as radiation fog or ground fog. On calm, clear winter nights, for example, heat absorbed by the ground during the day is then radiated into the air causing water in the air to form droplets near the ground. There are a variety fog types that form under different conditions. The title of foggiest place in the world goes to an area of the Atlantic Ocean called Grand Banks, lying off the coast of Newfoundland in eastern Canada. If you can see more than 1000 meters through the cloud it is mist, but if visibility drops below 1000 meters it’s called fog.ĭeserts regions, where cold winds meet dusty environments, or coastal areas where salt particles meet moist air, often results in thicker fog.

Fog is different from mist but only in how dense the cloud is, measured by visibility. Water vapour in humid air clings to dust and other microscopic particles to form water droplets that are suspended at ground level to create a cloud. The thickness of the fog, as well as the speed it forms and dissipates, dictates how hazardous it may be and how best to stay safe.įog requires very humid conditions to form.

These specific conditions also determine how quickly or slowly fog forms and dissipates. Depending on temperature and level of humidity it may be thicker or thinner, which leads to varying levels of visibility. Fog is essentially a cloud on ground level.

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