Radar Description
What Is Radar?
The Bureau of Meteorology Radar is a great instrument in showing where precipitation areas are within the Radar coverage zone. Although not always correct, it gives a general idea of where rain and showers are falling, as well as the location of thunderstorms, and the direction the rain is moving.
How It Works
The Radar does a loop/sweep of its area approximately every 10 minutes (360 degrees). The Radar is pointed in a straight line just above the horizon and the further away the Radar beam goes, the less likely it is to be accurate. It is also subject to variability and false readings (false echoes) E.g., It may sense a plane, flock of birds, but will not pick up heavy rain on the other side of a mountain as the mountain blocks the Radar beam. False echoes are shown as scattered blue dots that change location with each new Radar image, with very erratic movement. Also if there is an area of thunderstorms behind closer storms to the Radar, the radar may not pick up the full intensity of the storms further away. Also rain, light or heavy, may fall between radar loops of an area, and not pick them up.
Each Radar produces 2 images, the Local scale and the Broad scale. The Local Scale reaches a radius of 128km, and the Broad reaches a radius of 512km. The Local Scale is often more accurate than the Broad Scale, as the Broad tends to overestimate rainfall slightly, but the Local Scale can do this at times as well. Please visit "Interpreting Weather Watch Radar Images" Page for more information on specific Radar's in Australia and there limitations.
How to Read the Radar Images
Rainfall on the Radar is distinguishable by the table at the bottom of each radar image. This tells the approximate amount of precipitation falling per hour in a given location. Light showers and light rain are seen in the blue and light blue colours, moderate in yellow, green is heavy rain, while pink is heavy rain with possible hail and snow. Red indicates extreme rain and possible hail. Also shown on the radar image are the date and time in UTC, as well as the name of the location of the Radar. Also on the Broad scale, you will notice a shaded area. This is the area in which the radar has done a loop. Sometimes on the Radar loops, you will notice the shaded area disappears for a loop, and then is back in the next. This is because another radar has swept throughout the same area, but has "dropped out" for that loop for one reason or another. Also brown coloured areas are land and blue are the ocean.
Some Examples of Different Weather Situations and How They Appear on Radar
- General widespread showers with embedded heavier showers
- Scattered Showers and Rain,
- Isolated Thunderstorms,
- Squall line with Thunderstorms
Above is an example of widespread showers and rain, and how a Tropical Cyclone can look like on radar. The image is of Severe Tropical Cyclone Vance as it approached Exmouth Gulf in Western Australia. Note the clear spot in the center that is the eye of the Cyclone and the obvious circulation. As you can see there is a large area of blue and light blue over land, which over time can lead to widespread flooding.
The image above illustrates scattered showers. These are often coastal showers, not lasting long after they reach land or they are showers that develop with a trough or approaching cold front.
Above is an example of isolated thunderstorms. Note the heavy precipitation (pink/red) and the light blue area, which can indicate the direction of the anvil of the thunderstorm, but not necessarily the direction the storm is moving
And the image above shows a squall line situation, usually with an approaching cold front. Note the broad area of pink and green indicating heavy rain.
Further Information
If you have any further questions about the Radar, please email the webmaster of the Australian Severe Weather Association website, or your state representative.
I hope this has been an informative read and clears up any questions you may have about the radar.
Matthew Smith
A big 'Thank You' to the Bureau of Meteorology for the examples of radar imagery used on this page.