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Supercell thunderstorms set to batter south-east Queensland as BOM warns of 'giant hail', destructive winds

By Rory Callinan, Wednesday October 13, 2021 - 09:47 EDT
ABC image
Thunderstorms are expected to move across Queensland from the state's west bringing hail and destructive winds. - ABC

South-east Queensland should prepare for a battering on Thursday, with several supercell storms set to sweep in from the west, bringing "giant hail", the Bureau of Meteorology (BOM) has warned.

Having just copped a drenching on Monday, the region now faces a new destructive weather system that will be slow moving and likely feature severe thunderstorms with possible "giant hail",  which the bureau classifies as anything larger than 5 centimetres.

But the potential for tornados, such as the one that cut a swathe around Bathurst in New South Wales last week was low, meteorologist Dean Narramore said.

He said cold air coming across Australia was going to hit the warm, moist air coming in from the Coral Sea, and lead to an outbreak of severe thunderstorms that were typical for this time of year.

"It's looking like another big storm day," Mr Narramore said.

"It's kind of a combination of more moisture around the country providing more energy for the weather systems that do move through."

Tornado activity not likely

While the storms that produce giant hail and destructive winds are classified as supercells, they are unlikely to unleash tornados into built-up areas of south-east Queensland due to their arrival en masse. 

The tornado that hit the Bathurst region last week prompted speculation a similar weather system could form across Queensland but Mr Narramore said that was not likely.

Mr Narramore said the scenario where storms presented in a group, with several storms in close proximity to each other, lessened the chances of them producing a tornado.

He said a tornado was more likely when it was just one super-cell storm in the right atmospheric conditions, and not a group of four or five all competing for the same energy out of the atmosphere.

"As they [the storms] get closer to the coast they tend to all congeal together and if you get lines of storms and things like that then you are less likely to get tornados,'' Mr Narramore said.

"They need to be discreet isolated storms with all the right ingredients in place for a tornado to form. If there are five or six storms, they are all kind of fighting for that energy.

"There's a chance of those [tornados] further inland on and west of the ranges like the Darling Downs, but more so into northern NSW, but even then the chance is very low."

Supercells set to hit south-east

Mr Narramore said the bureau was unable to specify exactly where the storms were likely to be most severe until Thursday morning but predicted they would generally come from the west or north-westerly direction.

"It's not until the morning of day that we can see how the atmosphere is set up, where the converging wind boundaries and mountain ranges are that act as a focus point to provide a lifting mechanism to initiate the thunderstorms,'' he said.

"They're likely to come toward south-east Queensland from Kingaroy down through Toowoomba and Esk as they move off the ranges.

"Some of these storms could be supercells and it's these storms that have the potential to bring giant hail and destructive winds to some communities across inland south-east Queensland and north-eastern NSW on Thursday."

Heavy rainfall recorded

Over the past two days, heavy rainfall has been recorded with Mount Glorious receiving 75 millimetres, Beerburrum on the Sunshine Coast racking up 48mm and Brisbane 35mm.

Gatton and Amberley also had major rainfall, recording 36 and 38mm respectively ? the highest rainfall in four years in those areas.

Despite the high totals, the downpour has done little to shift the levels of the south-east's under-pressure water supply.

Wivenhoe Dam's water supply showed a slight increase from 40.2 per cent on October 6 to 40.7 on October 9 but then dropped back to 40.2 per cent on October 12.

Seqwater has warned water restrictions would likely come into effect in south-east Queensland if the combined total of the region's dams dropped below 50 per cent, which could occur by December.


© ABC 2021

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