... masses all occur in areas where surface atmospheric pressure is high and where wind speeds are usually slow, this aids the formation of a uniform surface as the slow moving air provides the time needed for temperature and humidity to equalize. Air masses move away from their origins due to surface winds blowing outwards from surface high pressure areas. This movement cause the air mass to alter, the different surfaces that an air mass travels over has a direct affect on its temperature and humidity, for example when tropical maritime air moves polewards its travels over surfaces cooler than its origin and so the surface layer is cooled. Polar Air Masses Affecting the UK With the air masses comes different weather, in the UK we are surrounded by mP, cP, mT, and cT air as you can see in the diagram above. The polar air masses are indicated by the arrows ...

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