Early starts are part of the appeal of recreational flying: a quiet airfield, soft light and the prospect of being home before the day gets busy. They also deserve a deliberate look at visibility and low cloud.
What makes fog worth watching?
The Bureau of Meteorology describes radiation fog as favoured by moist air near the ground, clear overnight skies and light winds. Cold air can collect in valleys, while nearby water can add moisture. Advection fog forms when warm, moist air moves across a colder surface and may persist for long periods.
Fog does not disappear on a timetable simply because the sun has risen. Thick fog or cloud above it can slow clearance. Conditions may also differ between a valley and nearby higher ground. A clear view from one spot is not proof of a clear route.
Make the uncertainty visible
When planning an early departure, write down what you still do not know about the route and destination. Separate a current report from a hope that conditions will improve. Discuss the relevant aviation forecasts and observations with your instructor if their meaning or coverage is unclear.
A useful personal exercise is to keep a ground-based morning notebook: forecast, observed conditions, location and time. Over several weeks, compare what you expected with what happened. Treat this as a way to generate better questions, never as a substitute for the flight’s current briefing.
Keep the day flexible
Decide ahead of time what you will do if the departure is delayed. A café visit, hangar job or theory session can still make the trip to the airfield worthwhile. Removing the need to “get something out of the day” makes a conservative decision easier to accept.
Further reading: Bureau of Meteorology: Fog (PDF).