The properties and movements of air masses are responsible for all the weather patterns we experience in daily life. An air mass is a large body of air, with a similar temperature and moisture content throughout. Air masses can be small or they can be gigantic, covering hundreds of thousands of miles. Air masses over water are called maritime air masses and contain a lot of evaporated moisture. Air masses over land are called continental air masses and are much drier.

A weather front is a boundary between air masses with different properties. There are four main types of weather fronts: cold fronts, warm fronts, occluded fronts and stationary fronts.

Check out the 2 Met Office videos for more details 

UK Air Masses

The main source regions are the high pressure belts in the subtropics (giving rise to tropical air masses) and around the poles (the source for polar air masses).

Warm source regions (tropical air masses):

• Sahara Desert – warm and dry
• Tropical Oceans – warm and moist

Cold source regions (polar air masses):

• Arctic Ocean – cold and moist
• Siberia – cold and dry
• Northern Canada – cold and dry
• Southern Ocean – cold and moist