Friday 25 October 2013


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Its all white outside and visibility is low, but what is the difference between a fog and a mist?

It has been said that fog feels eery whilst a mist feels empty.  I think this sums them up pretty well.
I remember once driving through dense fog for over an hour and it is so disorientating as if I was driving through outer space.

Both fog and mist are caused by microscopic droplets of water suspended in the air.  Light travelling through this space is scattered when it comes in contact with these droplets which results in reduced visibility and the white veil we are familiar with. The larger and denser the droplets are the worse the visibility becomes.


A fog is defined in meteorological terms as a very low cloud, often in contact with the ground. Fog droplets are larger than mist droplets, and are closely packed together.  This reduces visibility significantly and causes the cloud like fog.

A fog occurs when the relative visibility is below 1 km and the relative humidity exceeds 95%.
The most common cause of fog is cooling by radiation when the ground cools, causing a layer of air next to the ground to cool also. A fog starts to form and condenses heat, and so becomes cooler. Gentle movement of the air makes the fog thicker.

Fogs are more common in colder weather (autumn and winter) and often form during the night.
Ground fog (also known as radiation fog) often occurs over damp or wet ground after a rainy night or when clouds touch the ground. Sea fog (also known as Advection fog) is caused when warm air flows over cold sea surface, or even the land.


A mist comprises of small droplets suspended in air. The droplets are smaller than those present in a fog and not so densely packed.  A mist occurs when visibility is between 1 km and 2 km.

Mist is commonly seen in cold air above warm water such as in a bathroom, when you breathe out on a cold day or the steam of a sauna.

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