Balloons Over Bristol
Weather to fly?
On most sunny summer evenings, you can almost guarantee the skies over Bristol will hail the colourful sight of hot air balloons flying gently with the breeze. Bristol is the UK capital of ballooning thanks to Cameron Balloons, the largest manufacturer in the UK.
Ballooning is wholly dependent upon the weather ?? having no steerage, pilots are at the mercy of the winds ?? therefore the most important aspect when deciding to fly is the science of meteorology. All pilots must sit a compulsory exam in the subject in order to be safe in the air. This is something that you too can look at if you want to know whether you will see balloons in the sky on any given day??
Meteorology encompasses many aspects of the Earth??s atmosphere, including atmospheric pressure, temperature, wind and cloud formation - all of which are important factors in determining the weather we experience on the ground. You will normally only see balloons flying early in the day or just before dusk as these are the periods when the air is most stable for flying.
Wind is the term used to describe the flow of air over the Earth??s surface. Both the direction of the wind and its speed are important to balloonists and are given by meteorologists as two figures; e.g. 270/12 would denote a wind speed of 12 knots (Kt) blowing from a westerly direction (270?? true corresponding to West on a compass). In order to avoid flying over the River Severn pilots flying from Bristol would look for a wind direction blowing roughly from West to East. A wind speed below 10 knots is preferable or the landing can be fast and painful!. Generally, if you notice a lot of movement in the leaves of trees, sensible balloon pilots will not be flying ?? although this is more difficult to gauge in winter when the leaves have fallen!
Looking at the clouds will also give you an indication of whether it is a flyable day. Clouds are divided into four main groups for identification: cirriform (fibrous looking); cumuliform (heaped); stratiform (layered clouds); nimbus (rain-bearing clouds). Clouds are then further divided according to the altitude (or height) at which they form. Generally, thick flat grey clouds are bearing rain or snow and are therefore indicative of poor flying conditions. Heaped fluffy cloud with a dark base may also yield rain and any clouds forming with a vertical ??tower?? are the balloonist??s nightmare as these hail a thunderstorm and very unstable conditions unsuitable for floating in a bag of hot air!
Submitted by: Marie Orchard, 10 September 2004
