It has been quite a run of cold night for the southeast inland, waiting for high pressure to move on through to the east to move the region into a warmer northerly flow.
That looks to be still a few days away with a number of cold nights to continue, though the frost risk will contract into southeast NSW and elevated portions of VIC.
Fog will become a bigger feature as we run through this week, with an easterly pattern developing, bringing in low level moisture through large parts of eastern Australia.
Combining with the relatively clear skies over inland regions and cooler nights with the light winds, it is the perfect recipe for fog to form.
You can see the influence of easterly winds wrapping around the high pressure in the Tasman Sea to bring in the low level moisture/higher humidity values into eastern Australia. Once that encounters the cool stable air over inland regions, with the light winds, fog will develop. It is known as the easterly dip fog.
The fog may linger a little longer in the coming days and be more dense, given the moisture profile of the atmosphere will be improving, knocking the dry air that has been around for a week, back into central parts of the nation.
But once the sun gets up to a relatively higher angle, the fog should burn off most days for regions impacted by 10am.
This may interrupt regional flights so be aware if you are heading away from your town.
Frost will be a low risk from mid week with the focus for only light and patchy frost at this time.