Record “grapefruit-sized” hailstones measuring 16cm in diameter hit the Queensland region of Yalboroo, north of Mackay, yesterday as severe thunderstorms developed across eastern parts of the state during the afternoon and evening.

The Bureau of Meteorology defines “giant” hail as 5cm or larger.

“Sixteen is well above that - I think it might be gargantuan-sized hail,” BOM Senior Meteorologist Dean Narramore said. “We are talking grapefruit-sized hail.”

Many of the hailstones photographed by “citizen scientists” were comfortably in the 12-14cm range, some penetrating car windshields, he said. The previous record for largest hailstone observed in Australia was 14cm, set a year ago during severe “Halloween” thunderstorms in south-east Queensland.

BOM says hail needs exactly the right conditions to form, and giant hail needs even more varied factors to come together and so this event is quite rare. Yesterday, central Queensland had a contrasting combination of very cold, dry air and warm, moist air.

“To get hail that size, a lot of things have to come together,” Mr Narramore said in a video posted by the Australian Broadcasting Corporation.

Some unusual things stood out yesterday, he says: the air above the surface was up to 8 degrees colder than normal, drawing very warm and humid air higher and freezing rainfall into hailstones. Secondly, the updraughts that sucked the warmer air higher were very strong, holding the hail up longer and allowing it to get larger before “gravity finally took over and they fell to the ground”.

Numerous reports from residents emerged of the giant hail and the BOM, which verifies hail size mostly through public reports, says analysts will investigate, checking if there is an objective measuring device next to the hailstone in a video or image, any associated damage, and if weather data corroborates the reports.

“Luckily we had some residents with photos of the hailstones next to some tape measures or rulers. That was a good idea. We will chat to those people and confirm and make sure it is the right measurement and we will back that up with radar data,” Mr Narramore said.

IAG told insuranceNEWS.com.au it has only received two motor claims so far, helped by the event taking place in a fairly remote area.

While giant hailstones above 12cm cause severe damage, and social media images showed a number of cars with shattered windshields, Mr Narramore says “you won’t see widespread destruction from big hail that size” as most of the hail would still be smaller.

Another round of thunderstorms with large hail, damaging winds and heavy rainfall is expected in Queensland today for some isolated communities. Some areas of NSW were also subject to severe weather warnings.

A hailstone measuring more than 20cm in diameter fell in South Dakota in 2010.