If you've looked at a satellite image of Australia today you've probably noticed an area of cloud across South Australia, extending into the Bight, but what caused it?

This cloud is due to a low pressure pressure trough and cold front. The trough extends from northern Western Australia over southern parts of South Australia, whilst the cold front is just to the south, extending out over the Southern Ocean.

In the satellite image below the cold front can be identified by the comma shaped cloud, the tip of which is just to the south of Kangaroo Island. It then sweeps south past Tasmania, stretching around 2500km south in the Southern Ocean. The centre of the low, from which the cold front extends, can be seen centre bottom of the image.

Himawari-8 Visible True Colour Satellite Image, morning of Thursday 23rd April

By meteorological definition, a front is the transition zone between two air masses of different densities. As differences in density are most often caused by temperatures differences, it follows that a front separates air masses of different temperatures.

There are a few different types of front, but what is a cold front? We already know that a front marks the boundary between two different temperature air masses, but now we need to know if the colder air is behind or ahead of the front. In the case of a cold front, the colder air is behind the front, and advances east, replacing the warmer airmass ahead of it, with the colder air near the surface and the warm air rising above it.

Knowing this, it follows that as a cold front crosses a region, temperatures will drop. Here in Australia, ahead of the cold front, winds will generally be from a northerly direction, drawing air from the hot interior. As the front passes the winds shift to south, drawing much cooler air originating over the Southern Ocean.

Have a look at satellite images over the next few days and see if you can spot any of the cold front crossing to the south of Australia over the next week.