Cyclists, joggers,early morning motorists and those unlucky enough to be heading to work on a Saturday would have been greeted by a dense bank of fog over western suburbs this morning. The fog blanketed areas west of Blacktown, extending over Badgerys Creek and Campbeltown in the south and into the northern Illawara. Visibility went down to as low as 200 metres in Richmond. Locations north of Hornsby also experienced the eery humidity, as fog stretched all the way into the Lower Hunter. Although fog in summer seems out of place, all the ingredients for the foggy conditions were present this morning. The relatively cloudless evening and early morning meant the warm, moist airmass was cooled rapidly enough overnight for moisture to condense into fog. Moisture near the surface was also partially trapped by a phenomenon known as an inversion, where temperature briefly increases with height in a layer of the atmosphere. Onshore winds and occasional showers and thunderstorms from the interior are likely to enhance low level moisture in coming days, meaning that residents over western parts of Sydney have possibly not seen the last of their foggy mornings for the year.