A front marks the boundary between two air masses of different density. It is really important to remember that air masses never mix- its just physics! There are three types of front. Cold WarmOccluded Here the warm and cold air have caught each other.

Here we can see the cold front, this is also called a leading edge, it is the start of colder air. Ironically, the air coming is colder than this air… what do I mean?

In a more simple format it looks like this…. But this leaves a problem, how do they pass each other?

Cold Warm Cold Warm Stratus cloud- continuous rain. Cumulonimbus thunder and lightening.

When warm air meets cold air, the warm air is forced to rise over the cold air, this is because it is less dense. As the warm air rises, it cools, condenses, forms nimbo-stratus clouds and there is continuous rainfall.

When cold air meets warm air, the cold air is forced to sink under the warm air, this is because it is more dense. As the cold air sinks it forces the warm air to rise. As the warm air rises, it cools, condenses, forms cumulu- nimbus clouds and rains. This collision of air is particularly violent, often there may be thunder and lightening.