A unique weather phenomenon stretched for hundreds of kilometres across the New South Wales coast today, fascinating onlookers.
A long and rolling line of cloud was spotted by Sydney residents from Blacktown to Parramatta and covered the entire city by mid-afternoon.
For about three hours, the cloud stretched for about 300 kilometres.
The cloud was also visible over the Sydney Harbour Bridge and the Opera House.
Despite the cloud’s extra-terrestrial appearance, Bureau of Meteorology senior meteorologist Christie Johnson said there was a simple explanation.
“These are what we call altocumulus volutus – that’s the Latin name,” Johnson said.
“They’re clouds that form high up in the atmosphere.
“They are a rare phenomenon, you need to get the right mix of ingredients.
“It’s not 100 per cent clear what’s kicked off these particular clouds.
“It takes sort of quite specific conditions to get these clouds which is why they are rare.”
Written by: Emily Bennett.
This article was originally published on 9NEWS.