Depressions are low pressure weather systems that produce cloudy and rainy weather conditions.
Depressions develop when warm air (possibly tropical maritime) meets cold air (possibly polar maritime).
The boundary between the different air masses is called a front.
Depressions show up clearly on satellite images as great swirls of cloud.
Depressions bring a sequence of weather changes as they pass over head. Due to the rising of air caused by the movement of the fronts and interaction between the warm and cold air there are lots of clouds and precipitation.