It was a warm and foggy start to the last weekend of winter for coastal Queensland. Thick fog reduced visibility to just 50 metres at Rockhampton this morning and as low as 100 metres in Mackay, Proserpine and Maroochydore. At Mackay, fog was still thick enough at midday to keep visibility down to just 500 metres. Humid northerly winds on Friday loaded the air over eastern Queensland with plenty of moisture from the Coral Sea. A low pressure trough approaching from the west then allowed winds to become calm this morning, providing the ideal conditions for fog to form. Mackay only needed to cool down to 20 degrees this morning for fog to develop, simply because there was so much moisture in the air. This was no hard task, given that the average daily minimum temperature for August is 14 degrees. The temperature at which water vapour in the air condenses into fog is called the 'dew point' and for Mackay, this morning's dew point of 20 degrees was six above average. Fog is a risk for places like Mackay and Rockhampton again on Sunday and Monday morning, with light winds expected to coincide with high dew point temperatures.