Brisbane storm: What is a 'supercell'?

The storm injured a dozen people in Australia's third-largest city

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The Independent Online

The Australian city of Brisbane is in recovery mode after experiencing its worst storm in decades: a lethal mixture of wind, rain and hail ripped off roofs, flooded streets and injured several people.

The country's third-largest city saw around 90,000 homes without electricity on Friday, according to the state-owned supplier Energex, after power lines were downed by winds of 87mph. The power outage trapped commuters on electric trains for several hours when the storm hit on Thursday afternoon.

News footage showed windows smashed, light-planes flipper and cars disappearing on the flooded streets of the city, home to 2.2 million people.

Queensland state Premier Campbell Newman said the storm was the worst to hit the city since 1985, with 12 people suffering injuries.

The storm, classed as a Category Two Cyclone, has been called a “supercell” storm by meteorologists, and is thought to have caused $100 million (Australian dollars) worth of damage.

What is a supercell storm?

Eddy Carroll, chief forecaster at the Met Office, the UK's national weather service, spoke to The Independent about what causes a supercell storm.

"A supercell is a very large thunderstorm," Carroll explains. "Normally thunderstorms occur in relatively small structures and are self-limiting: when they grow and develop they precipitate and this kills the updraft (a current of rising air) that feeds them.

"In certain conditions, a thunderstorm can become self-sustaining: the updraft and the downdraft feed off each other and it grows and grows and becomes long-lasting. By becoming long-lasting, it can support hail; hail is heavy and relies on a strong updraft and because the storm lasts longer it can develop a strong updraft that is not interrupted by the downdraft.

"You can get tornadoes formed too or even strong straight-line winds where the downdraft hits the surface and spreads out."

When Carroll describes a supercell as long-lasting, that means it can occur for between six and 12 hours, whereas a normal storm will only last a couple of hours until it kills itself off.

Caroll explains that while supercells are rather rare, certain continental climates favour them: they occur in the midwestern United States and there is a "hot spot" in Eastern Australia.

That's not to say, however, that they cannot occur in the UK.

"The first supercell storm that was described over the UK is where the whole theory behind them started," Carroll explains.

"In 1959 there was something called the Wokingham Storm in Berkshire and it just so happened it was one of the first opportunities to study something like this in detail and really piece together what went on."

The storm was studied by a student who went onto work at the Met Office, Keith Browning, along with Frank Ludlam: the fathers of the supercell storm.

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