Fog???
 

Does anyone know how and why fog is formed? Is it more than just greater humidity in the air? Is it just really low cloud? What is fog?

When the dew point and temperature are the same it causes fog to form.

Water vapor in the air condenses when the temperature drops to or below the dew point. At the dew point, the air is too dense to hold the amount of water vapor in the air. It's the same idea as sugar crystallizing out of water as it cools in order to make rock candy. (I know it's not exactly the same, but it's an easy to understand comparison)

This is essentially correct.

When you super-saturate a solution, the solute (particles held in suspension in this case) will be forced out of solution (the air in this case) at a certain point (in this case, the dew point).

An interesting related note:

Cold air can hold far less water in suspension than warm. This is why the air is more dry during the winter time. Hwoever, in some areas this effect is countered by sublimation of snow.

Another interesting point:

When it rains, the air temperature will increase slightly. This is due to the breaking of many water-water hydrogen bonds as the water droplets fall. The reason it appears to be colder is because water has a high specific heat capacity (4.18 J/'C) and will conduct heat away from your (warmer) body (entropy).

Thanks guys. Whats a dew point though?

Dew point is just the calculated temperature that dew will form based on the humidity.

And just to save time: Dew is that stuff that gets your shoes wet when you walk through the grass in the morning. :D

:D

Cool. Thanks all.

low clouds?

The dew point is the temperature at which the air can no longer hold all the water vapor (humidity) present.
Warm air can hold a lot more water vapor than cold air.
That's why most fog "burns off" by late morning. It really doesn't burn off, but as the air becomes warmer, it is able to absorb the water vapor.
That's also why - barring a weather front moving through - the (relative) humidity is always higher in the morning, goes down throughout the day, and then rises after the sun goes down. Relative humidity is a function of air temperature and the amount of water vapor present.

Yeah Man,

When the temperature is low and the moisture content is high the relative Humidity rises until water vapour begins to mist. If this process continues and the relative humidity continues to rise it will form water droplets on any sharp cornered surface. If it still continues to rise then it will rain. Fog and Clouds form a little differently but are exactly the same thing.
skippy