Polar Continental

The polar continental air mass has a source region over the Eurasian land mass north of 50° N and east of 25° E. It is only a winter phenomenon, as in summer months the land mass becomes very warm, and there are no high-pressure cells developing to 'push' the air over the country.

Polar continental air affects the British Isles when there is high pressure over Scandinavia and surface winds are blowing from an easterly direction. The characteristics of the air depend on the length of the sea track during its passage from Europe to the British Isles. The air is inherently very cold and dry and it can reach southern Britain after a short sea track over the English Channel, producing weather characterised by clear skies and severe frost. If there is a longer sea track over the North Sea, the air becoming unstable and moisture is added, giving rise to showers of rain or snow. This can be a hazard, especially near the east coast, when the air mass passes over the warmer seas before reaching the colder land surface.

This type of air mass usually creates the UK's lowest temperatures, with temperatures falling below minus 10°C at night, and sometimes remaining below freezing during the day.

Polar continental air only reaches Britain between November and April; at other times of the year, the source region is neither cold nor snow covered and winds from north-eastern Europe bring a more tropical continental form of air.