Sustained Sydney fog

Hannah Wilson, 7 July 2019

Residents right across Sydney would have woken up to a thick layer of fog which blanketed the city and its surrounds this morning; persisting in some areas until after 10am as light winds struggled to clear it. 

This thick fog was as a result of a few persistent showers which fell overnight, adding to existing surface moisture. As the sky cleared of cloud cover, the surface rapidly cooled allowing the thick fog to form. Allowing this fog to persist for most of the morning was a strong inversion layer. The air above the inversion is warmer than the surface air and so it trapped the fog at the surface, with Road Weather Alerts issued by the BoM for all Sydney suburbs. 

Visibility was as low as 100 metres in Bankstown at 6am and still only 500 metres at Sydney Airport at 9am and 800 metres at 9:30am. This led to numerous flight delays and cancellations for the airport. It has been six years since visibility from fog remained below 1000 metres after 9am.

Not only was Sydney affected, with the thickest fog actually experienced in Bathurst as well as the Hunter and Illawarra regions. Nelson Bay in the Hunter was still recording a visibility below 50 metres at 9am this morning. 

Foggy mornings are a common occurrence during winter as minimal cloud cover allows the Earth’s surface to cool rapidly overnight. Therefore we should continue to see many more foggy mornings continue over this season.