Australian Weather Calendar: August 2015

August photograph by Peter Elfes

Fog covers the desert near Kati Thanda – Lake Eyre, South Australia

In 2012 much of Australia's semi-arid interior was recharged by floodwaters from Queensland. Water in Kati Thanda – Lake Eyre, usually a salt pan, provided moisture for the fog in Peter Elfes' photograph. 'So much water in an area that normally doesn't have it,' he says, 'creates weather situations that you don't normally get to see.'

Fog forms when water vapour condenses into tiny droplets of liquid water suspended in air. When visibility is greater than 1 km this phenomenon is called mist, but when visibility is reduced to less than 1 km it is called fog. Radiative cooling of the ground overnight can result in the formation of fog—given sufficient moisture, light winds and clear skies. In the hours following sunrise, fog often 'burns off' as the sun's heat evaporates the water droplets.

'This fog was actually over the water,' recalls Peter, 'then as the morning sun comes up it creates a breeze... and then the breeze blows the fog over the desert.'

Peter took this picture from a helicopter, at about 120 m off the ground, with a Canon 5D Mark III camera at focal length 24 mm.