Depressions

Weather fronts

A depression is an area of low pressure which moves from west to east in the UK.

Low pressure systems can be identified from a synoptic chart due to:

Warm front

In a low pressure system the warm front is the first to pass over. This occurs when warm air meets cold air and the warm air rises above it. Warm fronts bring steady, continuous rain.

Warm front

Cold front

The next front to pass over is the cold front. Cold fronts bring heavy rain showers.

Cold front

Occluded front

When the cold front catches up with the warm front the result is an occluded front. Occluded fronts bring sudden downpours of heavy rain.

Occluded front

All three fronts are associated with rain.

Watch the following clip to help you make sense of weather fronts.

Frontal rainfall

Depression characteristics

  • Wind - winds blow anticlockwise in a depression and along the isobars; where isobars are close together, wind is strongest.
  • Wet - where warm air meets cold air, the warm air is pushed upwards, it cools, condenses and clouds form.
  • Temperature - in general, the warm sector behind the warm front brings warmer temperatures and the cold sector behind the cold front brings cooler temperatures.

As a depression passes over the following changes occur.

Characteristics of a depression Characteristics of a depression