Air masses

The five main air masses

An air mass is a large volume of air which travels from one area to another. The weather an air mass brings is determined by the region it has come from and the type of surface it has moved over.

There are five main air masses which affect the UK.

Air masses affecting the UK

To describe and explain the weather that air masses bring consider the following:

  1. Where has the air mass come from - is it the north (cold air) or the south (warm air)?
  2. Has the air mass passed over sea or land?

These two pieces of information will help you name the air mass and describe its characteristics. The basic ideas are as follows:

Source AreaCharacteristics

Weather characteristics

You should learn the information in the table below.

Weather characteristics
NameSource areaWeather characteristics
Tropical Maritime (mT)Atlantic OceanWarm and wet
Tropical Continental (cT)Southern Europe and North AfricaWarm and dry
Polar Maritime (mP)North AtlanticCold and wet
Polar Continental (cP)Northern EuropeCold and dry
Arctic MaritimeArctic OceanVery cold and wet

The temperature of an air mass is also determined by seasonal changes. Temperatures in the summer months are always higher than in winter months.

The air mass known as the Arctic Maritime does not occur very often, but when it does it brings heavy snow.