Why is there fog over water?
Fog, dew and clouds are all related. In order for fog to form, the moisture must leave the air and condense. This means it must be cooled in some way, because cooler air cannot hold as much moisture as warm air. When the air is cooled below a certain point, called the dew or saturation point, then fog starts to form.
One of the conditions in which fog forms is when a mass of warm air passes over a cold area of water. Or it could be the opposite, with cold air passing over warm water. The currents of warm and cold air mix gently and you get those familiar fogs which seem to hang in mid-air over a body of water.
Why is snow white?
Snow is actually frozen water, and as we know ice has no colour, why then is the snow white? The reason is that each snowflake is made up of a large number of ice crystals. These crystals have many surfaces. It is the reflection of light from all of these surfaces that makes snow look white.
Snow forms when water vapour in the atmosphere freezes. As the vapour freezes, clear transparent crystals are formed. The currents that are in the air makes these crystals go up and down in the atmosphere.