How these giant balloons help predict S’pore’s weather from 35km in the air

MS Explains: How do giant weather balloons work?

Singapore’s skies have been dramatic lately, with thundery showers expected on most days in the second half of September.

Last September, a sudden and intense storm, bringing winds of up to 83.2km/h, took Singapore residents by surprise  — a reminder that our island’s weather can change on a dime.

In the midst of these sudden downpours, giant weather balloons help to track it all.

Released twice a day

It looks like something out of a children’s book — silent, round, and white — but this is no ordinary balloon; it is one on a mission.

Within minutes, it will rise tens of kilometres above the ground, quietly collecting data during its ascent.

This happens twice every day at 8am and 8pm like clockwork, says the Meteorological Service Singapore (MSS).

However, why does Singapore still rely on this seemingly ‘old-school’ method?

What can a balloon possibly tell us that high-tech satellites cannot, and how does it actually work?

Balloons capture a ‘vertical snapshot’ of the atmosphere

As it turns out, each helium-filled balloon carries a small device called a radiosonde.

This tiny instrument, about the size of a lunchbox, is what does all the heavy lifting.

As the balloon slowly ascends, the radiosonde transmits real-time data on temperature, pressure, humidity, and wind, said the MSS.

By the time the balloon reaches its limit — around 30 to 35 kilometres above sea level — it has captured a vertical snapshot of the atmosphere, top to bottom.

Eventually, the pressure causes the balloon to burst, and the radiosonde floats gently back down with a parachute.

While the balloon’s journey may be over, the data it collected lives on — powering everything from daily weather forecasts to long-term climate studies.

Back in 2019, Singapore’s Upper Air Observatory became the first equatorial station to be certified under the Global Climate Observing System Reference Upper-Air Network (GRUAN).

Our weather balloons do not just serve local forecasts; they also contribute to global climate research by helping scientists track long-term changes in the Earth’s atmosphere, from rising temperatures to shifts in wind patterns.

Why use balloons in a high-tech world?

In our era of satellite maps, AI chatbots, and hyperlocal weather apps, it might seem quaint, even outdated, to use balloons for weather forecasting.

However, according to Steve Yim, Director of the Centre for Climate Change and Environmental Health of Nanyang Technological University (NTU), radiosondes are still unmatched in one specific area: vertical detail.

“Radiosondes collect vertical atmospheric profiles of temperature, humidity, pressure, and wind — data that satellites often can’t provide accurately,” he explained.

This vertical view is essential in Singapore’s tropical climate, where the weather can change quickly and dramatically.

Radiosondes help forecasters detect these shifts by identifying patterns in the upper atmosphere, such as instability or moisture, that could trigger storm clouds.

Why the data matters in Singapore

Prof Yim said that surface-level observations are not enough for short-term weather forecasting in Singapore.

In the tropics, weather systems are small but intense — a downpour in Jurong might not reach Ang Mo Kio, wind patterns shift by the hour, and a thunderstorm can form in under 30 minutes.

That is why high-resolution data matters.

“To understand how weather develops, we need a three-dimensional picture of the sky,” explained Prof Yim.

By measuring the atmosphere in layers, from the surface all the way to the stratosphere, radiosondes help meteorologists see the full structure of a storm before it arrives.

This makes forecasts more accurate, especially in the short term.

The data goes straight into forecasting models

Once the radiosonde data is collected, it is fed directly into numerical weather prediction models.

These are complex simulations that forecast future weather based on current conditions.

“The vertical data helps initialise these models with a clear, accurate snapshot of the atmosphere,” said Prof Yim.

This process is called data assimilation, and it is crucial for modelling rain bands, thunderstorms, wind fields, and more.

In short: no balloon, no accurate forecast.

Satellites and AI are not replacements for weather balloons

You might wonder: what about satellites, or AI?

While both are important, with satellites providing broad views of global weather patterns and AI crunching enormous amounts of data and spotting trends that humans miss, neither can fully replace the humble balloon.

“None of any newer technologies can replace existing technologies because each technology must have its own advantages and disadvantages,” said Prof Yim.

“They are more likely to complement rather than replace weather balloons in the near term.”

He added that some atmospheric data cannot be retrieved from space, and that “radiosondes provide ground-truth measurements”.

In fact, balloon data is often used to validate what satellites see.

Without it, AI predictions may not be reliable, especially in regions like the equator, where the weather is less predictable and models struggle with accuracy.

Every forecast you see has a balloon behind it

The next time you open your weather app, think about this.

That forecast — rain at 3pm, or cooling winds by nightfall — may have started with a balloon drifting silently through layers of atmosphere, sending back whispers of what is to come.

These quiet observers help keep us dry, safe, and prepared.

They may be ‘simple’ and fleeting, but in the ever-changing skies of Singapore, they are indispensable.

Also read: Thundery showers on several mornings in 2nd half of Sept, with few dry days