Pilots at the Coupe Aéronautique Gordon Bennett were today warned of possible thunderstorm activity in Italy, on their potential flight path later this week. We explain why that is such a serious issue for balloon pilots...

Pilots at the Coupe Aéronautique Gordon Bennett were today warned of possible thunderstorm activity in Italy, on their potential flight path later this week.

Thunderstorms are serious business for anything in the air, and especially so for something like a balloon, which has no engine and no propulsion system. Drifting like a leaf a balloon literally blows where the wind blows, and that’s why thunderstorms are so dangerous – because they both suck in air and blow it out.

There’s a lot to how a thunderstorm forms, but in brief, they are formed when warm air rises and condenses to form a cloud, which becomes a bigger cloud, then a thundercloud and then a full-blown storm cell.

Certain meteorological conditions are needed to encourage the growth of thunderstorms, but take a low pressure system, add a good quantity of moist air and mix with some warm late-summer sunshine and you’ll probably cook up a decent storm.

These are the conditions forecast for later this week in Italy, which is where pilots might be flying to.

Thunderstorms can reach tremendous heights – up to 10,000m. The convection system that sets up inside them is like a feeding system: shovelling warm moist air in from the bottom and carrying it right up to the stratosphere where it cools and comes right back down again. (Warm air raises, cool air descends.)

This creates a pull-up, push-down circulation of air within a storm system.

The forces involved are enormous – there is a reason commercial jets avoid them, as they will be flung about inside the storm, making life very uncomfortable for passengers and crew alike.

In an open-basket balloon they are simply a no-go zone. Once caught in the circulation system of a thunderstorm pilots can do nothing but go up, come down, and go up again, waiting – and hoping – until they circulate out into clearer air.

Pilots who have survived flying into thunderstorms talk of hours spent counting their last seconds, struggling to breath as they are swept up to 6,000m or more, hailstones like snowballs, complete blackness and freezing temperatures. And then there is the lightning.

Another feature of a thunderstorm is they have gust fronts. These are ‘exhalations’ from the storm, where cold air comes crashing out of the storm system, along with rain or hail. Gust fronts can extend 30km in front of a storm and can mean rapidly descending air and turbulence.

Read more on thunderstorms here.

Illustration: The development of a thunderstorm. Credit: NOAA National Weather Service / Public domain