gravity wave cloud
Sydneysiders have been treated with a bizarre weather display after dozens of photos began circulating online of strange tubular clouds.

The eerie weather phenomenon was photographed and filmed over the city on Tuesday afternoon, with many querying what the reason was for the strange formations.

"Is it aliens?" one man asked. "I feel that as a society we all have the right to really know what is going on. Should we be concerned?"

Comment: Footage below - please note, contrary to the comment in the X-post, there's no evidence these are chemtrails. For further detail, see final comment:

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"What is going on?" said another. "Help."

But experts say there is an easy explanation for the unique cloud formations.

"These clouds are known as gravity waves," Sydney's 7NEWS weather reporter Angie Asimus said.

"In a westerly wind pattern, the air rises and cools as it goes over the mountains and then cools and condenses on the way down.

"The rise and fall creates these long clouds."

Although interesting to look at from the ground, Asimus warns the clouds could be trouble for air travellers.

"These (clouds) can also be a sign of turbulence for aircraft."