New Rainbow weather radar steps up the info stakes

New Rainbow weather radar steps up the info stakes

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Radar can tell you a lot about what rain is falling and where, but it's not a forecast.

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RADAR WORKS: The new weather radar at Rainbow resembles a giant golf ball on a tee, but provides much needed information for producers.

RADAR WORKS: The new weather radar at Rainbow resembles a giant golf ball on a tee, but provides much needed information for producers.

After years of campaigning the people of the Wimmera and southern Mallee were celebrating last week as work began on the Bureau of Meteorology's newest weather radar, just outside Rainbow.

Australia has more than 60 radars, with more on the way. But what exactly is a radar and what role do they play in forecasting weather?

'Radar' is an acronym for 'radio detection and ranging' and is a technology based on radio waves, which are sent out in short pulses. When these pulses hit water particles they reflect back to the radar as 'echoes'. The time those echoes take to return tells us how far away the rain is, while the strength of the return signal reveals the type of precipitation.

A colour scale is used to indicate the intensity of the rain-with black being the heaviest rain, sometimes indicating hail. A new image is displayed every 6-10 minutes, and these form a 30-minute loop.

It's important to note that this isn't a forecast: it shows you where the rain has been, so you can infer where it might go next.

Some radars - including the new one at Rainbow - also show wind speed and whether the wind is moving towards or away from the radar-these are known as Doppler radars.

Radars do have some limitations. The Earth's curvature means the optimal range is 5-200 km. Beyond that it could detect what's called 'virga'- rain that's falling but evaporating before reaching the ground. That's why sometimes you're staying dry, but the radar will tell you it's raining.

Low-level drizzle is also hard for the radar to detect because the droplets are so small and form close to the ground-it literally 'flies under the radar'.

There are usually no echoes displayed very close to the radar because the radar doesn't scan directly above itself. This is known as the 'cone of silence'.

Radars can also sometimes detect echoes from things other than rain, such as aircraft, smoke/ash, swarms of insects or flocks of birds.

Because echoes are created when the radar beam reflects off buildings or hills within about 20 km, and even mountain ranges further away. We filter this 'ground clutter' out of the final radar image but selecting a radar location that minimises these echoes is important.

Radio transmissions can also be mistaken for echoes from radar pulses. These usually appear as straight lines pointing towards a radar.

We are sometimes asked whether radars are dangerous; the answer is no, because they use a beam that's angled up into the sky and is constantly moving.

Radar is just one tool you can use to observe current weather. You'll get the most out of it when you use it together with other Bureau services, such as observations, satellite images, forecasts and warnings.

And remember, if there's a warning in place but you can't see anything on the radar, always follow the warning.

You can find out more about weather radars and plenty more in the Bureau of Meteorology's online blog page.

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