A New Zealander on holiday in the US captured some spectacular contrails while visiting California the other day.

Ian Forrest, a senior firefighter from Waikato, captured the jet vapour trails while visiting Yosemite National Park.

'Contrails are simply clouds that form when water vapor condenses and freezes around small particles that exist in aircraft exhaust,” says WeatherWatch.co.nz.

'In New Zealand we get a few contrails, especially over the South Island from flights travelling high above us as they travel from the Americas to Australia for example.”

Aucklanders sometimes see trails formed by flights from Fiji to Christchurch (which fly over Auckland at high altitude).

'Contrails are harmless - although after 9/11 when all flights were grounded in the US it was reported that air temperature rose by a couple of degrees due to the lack of contrails (clouds made by planes) in the sky.

'The reason for the pattern is because aircrafts fly in designated highways and lanes in the sky - and with so much air traffic in the US it doesn't take long in the right conditions to get the set up pictured above.”

Air traffic as of mid-afternoon Wednesday (late morning Thurs NZT) shows a line of flights tavelling along a highway in the sky - similar to what caused the contrail patterns above / Flightradar24