What are shelf clouds and how do they form during lightning and thunderstorms?

As torrential rain, large hail and lightning struck western Victoria on Thursday morning, a large plume of low-lying clouds began to gain momentum and move ominously across the county.

While the whirling dervish of the weather was a delight for photographers, it proved devastating for those with land in its way.

The circling column of cloud is called a “shelf cloud,” according to the Bureau of Meteorology.

“It's spreading ahead of the thunderstorms,” ​​said meteorologist Belinda House.

Shelf clouds, also known as arc clouds, form at the edge of a gust front.

According to the bureau, it is officially an elongated wedge-shaped cloud stuck to the leading edge of a supercell.

Cold downdrafts of wind essentially push warm, moist air upward.

“Warm, moist air is drawn into the thunderstorm… but then as the thunderstorm develops and you see the rain falling from the thunderstorm, the cool air crashes back to the ground.”

The devastation is great

The shelf clouds were accompanied by lightning and hailstones, some of which were 5 centimeters in diameter.

The storm cell leveled crops and destroyed dozens of buildings in areas such as Casterton, a farming town four hours northwest of Melbourne.

The state emergency service received 85 calls from the city, where cars and buildings were destroyed by the large hailstones.

“It's caused a lot of building damage – cracked windows, cracked skylights, cracked tiles, a lot of hits to cars from these huge hailstones,” SES spokesman Jamie Devenish told ABC Radio Melbourne.

Ms House said hail usually formed during thunderstorms but often melted before reaching the ground.

This means that much of the damage is prevented before it reaches a city.

“You don’t often see it reach the ground,” Ms. House said.

“But sometimes when severe thunderstorms develop, that hail can grow to a much larger size and therefore we may see significant hail touching the ground.”

The bureau issued a severe weather warning on Thursday for damaging winds across regional Victoria, with areas between Hamilton, Edenhope and Stawell.

A similar warning for damaging wind gusts remains in effect for the central mountain ranges in places, with a deep low pressure system expected across the state through Friday morning.