Australia Weather News

Lightning strikes have started multiple bushfires and destroyed at least three homes across Victoria amid searing heatwave conditions. 

More than 500,000 lightning strikes were recorded across Victoria and its coastal waters over a 24-hour period from midday Sunday as bushfires forced western Victorian towns to evacuate. 

Three homes have been destroyed by lightning: one from a direct hit in Taylor's Lakes in Melbourne's north-west, and two others when lightning started a bushfire south of Mildura. 

On Sunday, 114 new fires were started on private and public land most of which were ignited by dry lightning.

Fire authorities have issued repeated warnings about the phenomenon, but what exactly is "dry" lightning?

"Dry lightning is a thunderstorm that produces thunder and lightning and rainfall as well, but the rain evaporates as it falls towards the earth and none of it actually reaches the ground," said Angus Hines, senior forecaster at the Bureau of Meteorology.

Mr Hines said the cloud base with dry thunderstorms sat higher in the atmosphere, and that any rain produced fell through dry air and evaporated before reaching the surface. 

"Dry lightning is a major risk for bushfire ignitions because you get these lightning strikes, but you get no rain to suppress any potential sparks or ignition — and that's the real dangerous part," he said.

What are the warning signs?

The ABC's resident science guru Karl Kruszelnicki said it would pay to keep an eye out for something called pyrocumulonimbus clouds, which are formed by a rising column of hot air coming off fires.

"We're early on but the [currently burning] fires are massive," Dr Karl said. 

Dr Karl said around 80 such clouds have been discovered in the past 50 years, two-thirds of which occurred in Australia during the Black Summer bushfires. 

"And when I say these are massive clouds, mate, they punch higher than Mount Everest. They go into the stratosphere," he said

"Keep an eye on the weather, you might get some pyrocumulonimbus clouds happening."

How do you count lightning? 

Counting lightning bolts is no easy task. 

Special receivers set up across Australian skies detect any waves emitted during lightning activity — whether it be cloud-to-cloud or strikes that eventually reach the ground.

These pulses are found through the radio wave frequency, Mr Hines said, with each pulse hitting three different receivers. 

The time at which the pulse hits the respective receivers is used to triangulate where lightning struck. 

"It's a bit of a complicated process," Mr Hines admitted. 

"A little maths equation is done to determine where they've come from."

What is in store this week?

The lightning receivers will be working overtime over the next 48 hours, with thunderstorms forecast across regional Victoria and Melbourne on Tuesday. 

Conditions are set to relent somewhat on Wednesday as heatwave conditions ease. 

Of the 500,000 lightning strikes recorded during a 24-hour period to Monday, around 50,000 made it to the ground. 

Forest Fire Management Victoria's Chris Hardman said he was particularly concerned about the lightning that ignited bushfires in the Cape Otway National Park. 

While difficult to forecast the amount of lightning on the horizon, Angus Hines said thunderstorm conditions would persist. 

"Tuesday's another day with a fairly widespread thunderstorm risk across western and central Victoria, including around the Melbourne region," he said. 

"It'll likely be a combination of thunderstorms that do produce rainfall and some drier thunderstorms in the mix as well, which could create some hazardous fire conditions and damaging wind.

"It's another day where we need to be on high alert for those those fire threats."

ABC