Tropical Continental

Tropical continental air affects the British Isles predominantly during the summer. This air mass affects Britain when pressure is high over northern or eastern Europe with surface winds between east and south drawing hot air from North Africa. The air is initially unstable but very dry. It acquires some moisture in its passage across the Mediterranean Sea but it is still usually too dry to produce any significant amounts of precipitation. South-westerly winds at a higher altitude can occasionally inject sufficient moisture to produce high-based showers or thunderstorms.

Our highest temperatures usually occur under the influence of tropical continental air (over 30°C by day and around 15-20°C at night). Visibility is usually moderate or poor due to the air picking up pollutants during its passage over Europe and from dust particles blown into the air from Saharan dust storms. Occasionally, the Saharan dust is washed out in showers producing

coloured rain and leaving cars covered in a thin layer of orange dust.

Tropical continental air may affect the country from March to October, although it is most common in June, July and August. During winter months, tropical continental air is more difficult to identify, but may reach the UK on south or south-easterly winds ahead of slow-moving Atlantic fronts. When high pressure prevails during the winter, strong cooling near the surface makes the air stable, rather than cold and moist. Low cloud and poor visibility may be very persistent under such conditions.