Fog affected many areas of South Australia, Victoria and New South Wales and Queensland this past weekend and look like being a feature each morning well into the week in eastern states. A weak southerly change in the past few days has bumped up humidity, a necessary ingredient for fog development. The change was so weak that a high pressure system has taken over rapidly to cool the nights and convert the moisture into fog and low cloud, leading to low visibility lasting well into the mornings. Visibility dropped below 100 metres at Adelaide Airport, Loxton, Warracknabeal, Wangaratta, Griffith and Orange on Sunday morning. It stayed below 500 metres until after 10am in the Renmark, Mildura, Hamilton and Wagga Wagga areas before the lazy winter sunshine could burn it off sufficiently. With help from weak southerly change due mid-week, cooling nights under a high will convert moisture into fog and low cloud each night and morning through to at least Friday in Victoria, NSW and Queensland. Areas that are likely to be impacted by low visibility on at least one morning this week include parts of Adelaide, Melbourne, Canberra, Sydney and Brisbane, potentially slowing travel. In SA, the main fog time and place should be Monday morning and east of about Adelaide due to wind turning drier northerly.