What epic 'wall clouds' means for Aussie weather this summer

Australians have been captivated by striking images of the freak storms that battered large parts of the east coast over the past week. Powerful systems caused widespread destruction in some areas and triggered flash-flooding in others, leaving communities with huge clean-up efforts still underway.

In parts of NSW, including Sydney's metro, some regions recorded a whopping 100mm of rain in 24 hours.

Stunned locals watching the spectacle unfold took to social media to share their shots, with one, in particular, generating hundreds of reactions.

The photograph of "wall clouds" rolling in over the Woonona Rock Pool, at Bulli Beach just south of Sydney, was described by onlookers as "so cool" and almost "alien-like" in appearance. Some questioned what the phenomenon taking place actually was.

Speaking to Yahoo News Australia, Dr Ailie Gallant, associate professor at Monash University, said the reality is relatively simple.

Wetter-than-normal summer may mean more storms

Gallant, Chief Investigator at the ARC Centre of Excellence for Weather of the 21st Century, warned that as we head into what's expected to be quite a wet summer, we may well soon see more scenes like this.

"We often call these wall clouds," she explained. "There's a part of the storm called an updraft, and this is where the storm is basically sucking in air from around it.

"Storms have a lot of energy behind them and there's a lot of energy sucking the air into the storm. As it does so, it gets more and more powerful and what happens is that the air cools and condenses lower and lower.

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"That's when you get, what we call organisation at the bottom of the updraft of the storm, and then you get the wall cloud. They tend to be quite rectangular in shape and look like walls."

Gallant said the phenomenon occurs naturally "quite a lot", but the storm typically has "to be pretty severe".

"A wetter-than-normal summer has been forecast, which could — though it's hard to say definitively — mean more storms. December for Sydney is very much storm time, so it won't be surprising if you see more systems like this moving through." While the rain has eased slightly, authorities warned of the risk from saturated catchments and potential flash flooding in the coming days.

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