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Bristol Balloon Fiesta – what’s the ideal weather for ballooning?

Copyright: Bristol International Balloon Fiesta Ltd

Copyright: Bristol International Balloon Fiesta Ltd

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    Friday, August 08, 2014, 14:30 GMT -

    The Bristol International Balloon Fiesta is Europe’s largest annual balloon festival and the showpiece events – the mass balloon launches – are heavily dependent on the weather.

    **Forecast update - Great weather this morning for the balloon launch but showers expected to move towards Bristol into Friday afternoon and evening, with gentle to moderate southwesterly winds. Saturday morning looks dry but again by the afternoon it will become cloudier with some fleeting showers. The event could be hit by ex-hurricane Bertha on Sunday though. Heavy rain is expected at times and the wind will be strong so check the Balloon Fiesta’s twitter page and our website's forecast page regularly to see whether the balloons will fly. **

    The fiesta, which runs from 7th August - 10th August, attracts over 100 hot air balloons with around 500,000 people attending. As well as the balloon launches, there are over 200 trade stands, airshows and firework displays.

    But the biggest draw is the balloon launches that happen every day. These flights have been cancelled in the past because of adverse weather conditions.

    The most important weather factors are wind direction and its speed as pilots use the wind to steer the balloons.

    Light showers are ok but clearly not enjoyable for the riders or the pilots. Heavy showers though can cause difficulty in controlling the balloon. Visibility is another key factor, not just for balloon safety reasons – but it can also spoil the spectators’ view.

    On the appropriate weather for ballooning Don Cameron, Chairman of the Flying Committee, said: "Ideally we (hot air balloon pilots) would like clear skies and winds under 8 knots. But there are other things that we think about.

    “We also ask about the stability of the air which depends on the temperature profile with height. If it is very stable, as often happens after a night of clear skies, that is good. If the ground layer is warmer, it is less stable and upper air mixing and thermals will be expected to start earlier in the day.”

    When the sun comes, the ground heats up which in turn warms the air above. As warmer air is less dense than colder air, it rises in what is known as a thermal. This can make the atmosphere fairly unstable for balloon rides as the strength of thermals can be highly variable.

    “Sometimes cloud is an advantage, because it cuts down the solar heating and makes the thermals start later. Thermals are good for gliders, but bad for balloons because they make the flight path on landing unpredictable,” added Don.

    Pic: ©Bristol International Balloon Fiesta Ltd

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