An approaching cold front will bring showers to the state's west and far south, with 10 to 20mm expected in the west, and 1 to 5mm in the North-West, North coast, and far south.

Fog in the North caused headaches for the Launceston Airport and those attempting to travel in and out of the state on Sunday and Monday.

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Fog is a suspension of small water droplets in the air, says the Bureau of Meteorology.

It forms in the same way as a cloud, however the process takes place at surface level rather than higher up in the atmosphere.

For fog to form, air temperature needs to cool to the dew-point temperature - this is the temperature that condensation occurs.

The most common way of fog forming is air cooling overnight as the ground loses the heat it absorbed during the day.

A classic pattern for fog formation is to have rain falling late in the day, followed by the arrival of a high-pressure system that brings clear skies and light winds overnight. The rain increases the dew-point temperature, and the light winds and clear skies cool the air.

Fog reduces horizontal ground level visibility to less than one-kilometre. If you can see further than that, it's mist.

The foggiest city in Australia is Canberra, with an average of 47-foggy days per year.

Launceston Airport general manager Paul Hodgen said fog was a seasonal occurrence in Launceston, however it was highly unusual for the conditions to persist as they had earlier in the week.

For more information about fog, visit the Bureau of Meteorology website.