Anybody seen Melbourne? Or Ballarat, Horsham, Mt Gambier and a bunch of other places that disappeared in fog this Monday morning?

All the ingredients for a thick fog were in place overnight across a broad area of central and western Victoria as well as the southeastern corner of SA, including:

• Calm winds
• Cool temperatures with temps dropping to the dew point
• A moist atmosphere
• High pressure with a stable inversion layer

The two graphs below show how atmospheric conditions aligned perfectly for fog to form.

• The first graph shows how the temperature reached the dew point just before 11 pm
• The second shows how the wind died down to completely calm conditions a little earlier in the evening

You can see the dense fog that was still sticking around on the 9 am satellite image below.

That large arc of thick cloud extending from the Melbourne area out to the SA border and up around to the Murray near Echuca is all fog, not cloud. In some areas, visibility was down to just 100 metres.

READ MORE: What's the difference between fog and ground-level cloud?

One clue that the cloud in that satellite image is fog, not cloud, is the lack of any nearby radar activity.

The green blobs indicate precipitation, not just heavy cloud cover, and you can see rain (which is actually snow at high elevations in the NSW Snowy Mountains) falling to the east of the area mentioned, but none within it.

Image: Melbourne on the morning of Monday, August 28. Source: @Calendal on Instagram.

Meanwhile the fog started to clear as the morning progressed and the sun began to "burn it off". But it has taken a while and there were disruptions to air traffic at Melbourne Airport.

As often happens after foggy mornings, the day has started to warm quite quickly once the sun breaks through, with Melbourne tracking for a top temp of 18°C after an overnight low of 9.5°C.

Tuesday will be warmer again with a top around 20°C whole Wednesday should see a high of just 15°C as a cold front sweeps over southern Victoria. Gusty winds ahead of the front and after it will make it highly unlikely that we see a repeat of Monday morning's fog in coming days.