Australian Government Bureau of Meteorology

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Following a week of severe thunderstorms that produced giant hail across parts of Queensland and New South Wales, one of Australia's most accomplished hail researchers has explained how tiny stones can grow to the size of a ten-cent piece, a cricket ball or even the record-breaking size of a mango.

Hail can occur at any time of the year, but for large hailstones to form, conditions must be just right.

According to the Bureau of Meteorology's Dr Joshua Soderholm, in Australia, severe hailstorms are most common during spring and early summer.

“This is a time of the year when surface temperatures are warm enough to promote the development of intense thunderstorms, but you also need the accompanying ingredients of strong winds and cool air in the upper atmosphere to support hail growth,” Dr Soderholm said.

Earlier this month, the Bureau confirmed that a hailstone, which fell near Yalboroo to the North of Mackay in Queensland, had established a new Australian record.

Hailstones measuring 16 centimetres in diameter were observed, eclipsing the previous record of 14 centimetres set in 1991 in Kempsey, New South Wales and again in 2020 in southeast Queensland.

A recent storm at Coffs Harbour in New South Wales also produced large accumulations of small hail leaving what appeared to be a layer of snow on the ground.

"Hail starts as water vapour near the ground. This condenses into tiny water droplets, cooling as it rises inside a thunderstorm updraft, collecting really cold water that’s below freezing, Dr Soderholm said.

This freezing water is called supercooled water and the longer the droplets – and eventually ice - fly through the supercooled water within the hailstorm updraft, the bigger it grows.

"So, whenever you see giant or large amounts of hail on the ground, a lot has had to happen for it to get there. It is also why there is not hail in every storm."

Severe thunderstorms that may produce hail will continue about parts of the country this week.

The Bureau urges the community to stay up-to-date with the latest warnings at or via the BOM Weather app.

Australia is currently in a severe weather season that runs through until April 2022