The boom in air travel over the Easter holiday week has had a unique consequence for regional NSW, with residents in the state's north west reporting a dramatic increase in vapour trails filling horizons.
Also known as 'contrails', some people have photographed up to 10 at a time over Armidale, Tamworth, and the Liverpool Plains.
Weatherwatch director Don White said the phenomenon was caused by planes flying at high altitudes during cooler weather.
He said, above 8,000 metres, temperatures over the region dropped to below minus 30 degrees Celsius.
"[Vapour trails] are formed in the upper atmosphere, caused by the hot air from the plane creating ice crystals and water droplets creating a visible trail," he said.
There has been a boom in air travel due to Easter and COVID restrictions easing, and Mr White said aircraft travelling between major cities was the main cause of vapour trails because they had the highest flight paths over regional NSW.
"You don't get them near the airport," he said.
"Melbourne to Gold Coast, Sunshine Coast, or even Sydney to Sunshine Coast follow a circle over the Northern Tablelands and Tamworth region at maximum height.
Trails line up weather forecast
Although this week proved to have the perfect conditions for maximum vapour trails, Mr White said the sight would be short-lived.
"There will be fewer of them around after this week, as the upper atmosphere becomes more stable. But there'll be periods over winter where it will have more moisture," he said.
The spectacle had locals in the region sharing their vapour trail snaps on social media.
One Tamworth community weather Facebook page attracted more than 120 comments with locals sharing their experiences.
But on top of the photographic opportunity, Mr White said vapour trails could also help predict the weather.
"If they break up fairly quickly and disappear, the upper atmosphere is quite stable," he said.
"If they persist for longer, you can check the direction of movement.
"If they expand a little bit, there's a little bit of instability in the atmosphere and that usually indicates there's the potential for rain around."
