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Australian tornadoes flying under the radar but more common than you think, BOM warns

By Irena Ceranic, Friday June 8, 2018 - 12:02 EST
Audience submitted image
A tornado sweeps across the countryside close to a property at Greenhills, near the town of York east of Perth in 2012. - Audience submitted

They're quick, ferocious and hard to predict.

Tornadoes, while often associated with the Great Plains of the United States, are more common in Australia than people might think.

During the cooler months, cold fronts — which sweep up from the Southern Ocean bringing rain and strong winds to Southern Australia — will occasionally produce a burst of intense and violent weather in the form of a tornado.

On average there are five tornadoes reported in Western Australia's south during the cooler months, including two or three in Perth, but the actual number is likely to be higher.

Live fast, die young

Unlike tornadoes in the US, which can travel hundreds of kilometres, occur mostly during spring and summer and can last for hours, Australia's cool season tornadoes typically exist for about 10 to 30 minutes.

Bureau of Meteorology severe weather manager Bradley Santos said they normally occur between May and September.

"We call these systems 'cool season tornadoes'. They are different — they tend to live fast and die young," he said.

"They move at speeds of about 50 to 80 kilometres per hour and they can last as little as half an hour, but by that time most of the damage has been done.

"We've seen cool season tornadoes reported as far north as Geraldton, as far east as Esperance and even inland in the Kalgoorlie area, but the majority of reports come from the coastal strip between Lancelin and Walpole."

A tell-tale sign that a tornado has swept through an area, rather than a severe wind gust, is the path of destruction it leaves behind.

"Typically if the damage occurs in a long narrow line that is one of the signs … the line does not have to be continuous," Mr Santos said.

"They typically have paths of around 50 to 150 metres wide and several kilometres long.

"Damage to houses in their path can range from minor roof damage through to complete demolition of property."

Last year, leaving a trail of destruction across Sorrento, Duncraig, Warwick, Hamersley and Balga.

But it paled in comparison to on May 16 2005, packing winds of up to 200 kilometres per hour.

It caused $50 million in insured losses and forced the closure of the local primary school for four weeks.

On the same day, leaving a swathe of destruction through the town.

On September 22, 1993 a tornado in Mandurah demolished eight houses and damaged another 100.

Hard to predict

While forecasters can predict the environment in which there is potential for tornadoes to form, they cannot pinpoint exactly where they are going to hit.

Due to their small size, they can even be difficult to identify on radar.

"Some of the stronger tornadoes will have a definite radar signature, but because they are short lived — we have radar scans at every six minutes — it is possible for a tornado to touch down and dissipate in between those radar scans," Mr Santos said.

"The majority of the cool season tornados occur with the passage of a cold front, some can also occur in the very cold unstable squally airstream behind a front."

But Mr Santos said the other challenge for forecasters was that the majority of tornadoes did not occur during a severe storm system.

"So when that occurs, the majority of residents through Perth and the South West of WA wouldn't have experienced a strong cold front, yet we can have these narrow, short-lived strips of damage, and the damage is significant, very localised … but the majority of the area is damage-free," he said.


© ABC 2018

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