For a tornado to form, there has to be spinning air near the surface that gets dragged up and connects with a supercell thunderstorm.
“These are thunderstorms that have strong updrafts and pick up low-level horizontally rotating air, imagine a wheel of wind slightly above the surface, the thunderstorm picks that up and rotates it into a vertical rotating column,” he said.
“So you need a really intense storm with a really strong updraft and rotation happening within that as well. To have all those factors together are uncommon in Australia.”
However, Mr McDowell said tornadoes in Australia aren’t as rare as people might think, but may occur in rural areas and go unwitnessed.
“It does happen but it’s nowhere near as common as in Tornado Alley in the US, and usually not to the same magnitude,” he said.
“It does look like the Armidale one was worse than the one in Bathurst, likely because it was in a more populated area. We don’t have readings of peak wind strength but there were reports of flipping cars, damaged buildings.”
The Bathurst tornado also destroyed entire buildings and tore roofs off homes on its path between Bathurst and Lithgow.
Both tornadoes were a part of major storm cells that moved across the state.
On Thursday, hail and flash flooding hit parts of Sydney and the Hunter Valley, with a Westfield shopping centre in Mount Druitt evacuated after part of its roof collapsed.
Emergency services received nearly 500 calls for assistance across the state, nearly 200 of which came from Mount Druitt and Penrith in Sydney’s west.
About 30 also came from the Hunter Valley, which was hit with severe hail.
In Armidale, dozens of volunteers remain on the ground, with more on their way from the state’s northern regions and from Bathurst.
“We also got great support from the Rural Fire Service and Fire and Rescue NSW,” Mr Rankin said.
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