How is hail formed?
Today, Mika and I went for a walk near the mountains. Mika told me about the incredible experiences he’d had in the Arctic during the airborne measurement campaign. I listened intently and pictured the icebergs off Spitsbergen that Mika must have seen during the research flights. In doing so, I forgot that it was actually very warm. It was a glorious day with plenty of sunshine, and Mika was absolutely delighted to see flowering plants again and, above all, so much greenery.
When, at the end of our hike, we treated ourselves to a refreshing break outside an ice cream parlour with two large scoops of ice cream, we saw the sky suddenly obscured by a huge storm cloud. We sat down in the ice cream parlour and watched from the large window as large, white ice pellets suddenly fell from the sky. By a pond, you could even see how these ice pellets were causing the water to splash!
Well, why are ice balls falling from the sky? Fascinated by this, I asked Mika if he perhaps had any idea why ice balls were falling from the sky despite such a hot day. “An excellent question,” said a man sitting next to us suddenly, smiling as he looked out of the window. He introduced himself as Christian. He told us that thunderstorms both fascinate and frighten him in equal measures. Christian is a scientist and wants to tell us how these ice balls form on such hot days.
Temperature, he said, plays an important role in this, because hail – as these ice pellets are called – occurs mainly in summer. When a severe thunderstorm has built up, many water droplets are formed. Inside these storm clouds, many water droplets are carried upwards by powerful winds called updrafts. High up in the cloud, it is so cold that the droplets freeze into ice. This makes them heavier and they sink back down. As they do so, further water droplets can freeze onto the ice, so that the ice pellets become bigger and bigger. If the storm is strong enough, the ice crystals can be blown upwards again, growing steadily as they do so. Just like yo-yo, I thought to myself. This continues until the ice pellets are so heavy that they can no longer be carried by the updrafts within the cloud and eventually fall to the ground as hail.
Christian said that hailstones can grow as large as a scoop of ice and, in rare cases, even bigger. It’s truly unbelievable when I think about how dangerous it is when such large hailstones fall from the sky. Luckily, the storm soon passed. The sun came out again, the air felt cool and fresh, and we stepped outside to enjoy the rest of the day!
Text: Christian Buhren, Illustration: Patrizia Schoch, Translation: Fathima Cherichi Purayil