In short:
A Bureau of Meteorology weather balloon lifts off from the old RAAF Williams site at Laverton every day, carrying a small instrument box up to 35km into the sky before it bursts and parachutes back to Earth somewhere across Melbourne.
A Launch Pad You've Probably Walked Straight Past
Laverton sits on the Wyndham and Hobsons Bay border, better known these days for its train line, its footy and cricket clubs, and the RAAF history buried under Williams Landing. But tucked inside the old RAAF Williams grounds is something most locals have never clocked: one of the Bureau of Meteorology’s upper-air observation stations, where weather balloons are launched daily at 9.15am and 9.15pm.
Each release sends a hydrogen-filled balloon, roughly the size of a small car once fully inflated, rising quietly into the sky above the western suburbs. Attached underneath is a small white box called a radiosonde, along with a parachute or a foil-lined cardboard target shaped like a four-sided pyramid.
What The Balloon Is Actually Doing
As it climbs, the radiosonde constantly radios back readings of temperature, humidity, pressure and wind, feeding directly into the forecasts, warnings and aviation briefings issued for the whole of Victoria. It’s also part of Australia’s obligations under the World Meteorological Organization convention, which requires member countries to keep measuring the upper atmosphere.
Laverton is one of only 38 such launch sites across Australia and its territories, including Antarctica. Nationally, the Bureau sends up around 42 balloons a day, roughly 15,000 a year, each one feeding into the same global network meteorologists rely on to build accurate forecasts.
From Wyndham’s Skies To The Edge Of Space
The balloon keeps rising and expanding as the air around it thins, eventually reaching somewhere between 16 and 35km above the ground, well past where commercial planes fly and into the stratosphere. At that altitude the pressure difference is too much and the balloon pops.
From there, the radiosonde and its parachute drift back down to Earth, often ending up well outside Wyndham, anywhere across greater Melbourne, depending on the winds that day. A small but dedicated community of radio hobbyists tracks these flights in real time using online tools like SondeHub, and some head out to recover the instruments once they land, since the electronics inside can often be reused.
Watch a weather balloon being tracked.
If You Ever Find One
The Bureau says any weather balloon carrying its sticker, reading “Australian Bureau of Meteorology Radiosonde”, can be safely handled once it’s landed and deflated, though it’s worth washing your hands afterwards, since the balloon material is lined with talcum powder. Empty balloons can go straight in the household bin.
If you spot one still inflated, the advice is to stay at least 10 metres back and call 000, since it may still contain flammable hydrogen gas. And if you do find a Bureau radiosonde, they would like to know about it. There’s an 8-digit code on the bottom right corner of the unit that tells them exactly where and when it launched, which can be reported through the Bureau’s website.
So next time there’s a strange white dot drifting silently over Laverton’s skies, there’s a good chance it started its journey just down the road.
