Air masses affecting the British Isles

The British Isles have variable weather that changes from day to day, between different regions and within different regions.

Consequently, it is very difficult to predict or forecast the weather.

An air mass is a large body of air that is usually thousands of kilometres wide.

It will remain over a place for a period of time and will pick up the key temperature and moisture characteristics of that area.

It will then start to move.

The variability of weather and climate in different regions of the British Isles is due to the different air masses over the Isles.

Each air mass brings with them different characteristics, as shown in the map below.

Illustration showing the four air masses that affect the UKAir masses affecting the British Isles

The four main air masses that affect the British Isles are:

Tropical maritime (warm and moist air)

  • Air moves from the warm south Atlantic ocean and moves over the south west of the British Isles.
  • Mild conditions in the winter but wet weather in the summer.
  • Brings nimbostratus clouds, drizzle and fog.

Tropical continental (warm and dry air)

  • Usually only works in the summer.
  • Warm, dry air from North Africa and the Mediterranean bring warm, dry weather.
  • Will bring mild conditions in the winter.

Polar maritime (cold and moist air)

  • The most common air mass, starting in the North Atlantic ocean.
  • Brings unstable air that creates cumulus and cumulonimbus clouds.
  • Can cause convectional rainfall in the summer.

Polar continental (cold and dry)

  • Occurs more in the winter than the summer.
  • Starts over north Europe and brings cold conditions in the winter but milder conditions in the summer.
  • Can bring unstable air in the winter (producing snow) but usually just brings cool, dry conditions.