Weather Fronts

An area of air has properties that are affected by where the air has come from and the route that the air has travelled. An area of polar air will be cold. It can't mix with warm tropical air, and the area of transition between the two different air masses is called a 'weather front'.

Cold air is denser and therefore heavier than warm air, so lighter, warmer air has a tendency to rise above it. As the air rises it cools and the moisture contained within it condenses into clouds and eventually it rains. This is why it often rains as a warm front passes.

A cold front is shown by a line with blue triangles pointing in the direction the front is travelling. In the UK, a cold front often follows a warm front. Cold fronts travel faster, so can catch up with the leading warm front. The area of warm area behind the warm front is forced up over the cold air as the cold front approaches, and the cold air behind the cold front will also be pushing under the warm air. This means the warm air can be forced totally off the ground and this is called an occluded front. Fronts are only models. They are the perfect scenario, and in nature of course, things are rarely so cut and dried.

Sometimes it is difficult to tell exactly where the front is. Simply watching the temperature can be misleading. If the sun comes out after a cold front has passed, the temperature may actually rise. The clouds and rain are a better indication, as is a usual change in wind direction. However, mother nature works in mysterious ways and if she doesn't want to follow a model, she won't!