Weather radars detect rain. Meteorologists use radar images to track and forecast the movement of thunderstorms, tropical cyclones and other areas of rain. Radars also sometimes detect aircraft, smoke plumes, insect swarms, birds and other objects in the atmosphere, so care needs to be taken when interpreting the patterns shown on a radar image.
A good way of telling whether a pattern on a radar image represents rain is by following its movement from one scan to the next. If it is quick and erratic, or disappears after only one frame, it was probably not real rain. If the pattern moves slowly and consistently from one scan to the next, chances are it is real rain.
The radar images not only shows the location of rain, but also indicates on the map the coastline, local topography, roads, rivers, town names and forecast district boundaries. The lightest shade of green represents light rain, going all the way up to purple, which shows very heavy rain or hail.
There are 15 levels of rain intensity - shown in the legend near the radar image. Both zoomed-in and zoomed-out images are provided for most radars.
20:14 EST As the sun set over Melbourne, a thick fog engulfed the city.