Heavy fog has brought a gloomy start for Sydney with visibilities falling below 50 metres in places. Many parts of Sydney have been affected this morning. Even the CBD and harbour have seen visibility reduced to less than 100 metres. Some patchy rain last evening and overnight provided the moisture to develop the gloomy conditions. During the early hours the cloud that brought the rain cleared, allowing temperatures to fall rapidly, condensing the moist air at the surface as a result. Fog is affecting the airport too, with visibility reported below 500 metres. The fog will likely burn off rapidly this morning after sunrise leading to bluer skies and just the chance of a shower later.