Why did it hail ‘golf ball-sized’ ice in the middle of a heatwave in Germany?

It was a hot summer’s day – as warm as 30°C- when huge hail balls rained from the sky and painted the ground white.

It sounds like science fiction but it happened for real in the German village of Sipplingen, near Lake Constance in the south of the country, on Tuesday.

The half-hour storm saw residents battered by 5cm long hailstones, with the hail piled up half a metre high.

The unexpected weather freaked out unsuspecting tourists.

One couple told the German broadcaster SWR: ‘The hail was pouring down the street in masses. You started to worry about whether the water and the hailstones might reach your room.’

Around 50 firefighters were needed to clear up the hail, with 14 basements flooded by the hail blitz.

Despite the chaos, the sun was shining again by the afternoon.

While it may seem like a freak weather event, hail during a heatwave is a perfectly natural phenomenon.

Hail the size of golf balls battered Austria last week and it once hit the UK.

After three weeks of blazing heat in the 2013 summer, south Londoners were rocked by hailstones overnight.

So how is this even possible? Well, it has everything to do with the temperature of the sky.

Dr Pete Inness, teaching fellow in meteorology at the University of Reading explained to The Guardian: ‘Even on a sunny day, the temperature falls rapidly as you go up.

‘It can be 30°C on the ground but the temperature falls by about 10°C for every kilometre you go up – so the freezing level is around 3,000m above the ground.

‘Hail forms in a cloud that is somewhere between 3km and 10km above ground. At the top of the cloud, 10km above ground, the temperature could be -59°C or -60°C.’

To be more specific, hail forms in a cumulonimbus cloud, which are giant clouds that cause storms.

Hail can actually be more common in the summer months because we see the formation of more cumulonimbus clouds due to moisture in the air.

The hail builds up inside one of these clouds, getting bigger and bigger until they are too heavy and drops.

Hail does gradually melt as it’s on the way down to Earth, but if the cloud is cold enough, it will still be a frozen ball by the time it lands.

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