What Is a Weather Balloon?
A weather balloon is a large balloon used to carry instruments high into the atmosphere to collect information about temperature, humidity, air pressure, wind, and other atmospheric conditions.
Weather balloons are an important part of modern meteorology. As a balloon rises through the atmosphere, an instrument package called a radiosonde takes measurements and transmits the data back to a receiving station on the ground.
Meteorologists use this information to understand conditions above the Earth’s surface and improve weather forecasts, computer forecast models, and severe weather analysis.
Weather Balloon Quick Facts
| What it is | A balloon used to carry weather instruments into the atmosphere |
| Primary instrument | Radiosonde |
| Measures | Temperature, humidity, air pressure, and other atmospheric data |
| Wind data | Determined by tracking the balloon’s movement |
| Typical material | Latex or another flexible material |
| Maximum altitude | Often around 30–35 km, although altitude varies |
| What happens afterward | The balloon expands and eventually bursts, allowing the instrument package to descend |
| Used for | Weather forecasting, atmospheric observations, research, and forecast models |
How Does a Weather Balloon Work?
A weather balloon begins its flight from a ground-based launching station. The balloon is filled with a lighter-than-air gas, typically helium or hydrogen, which causes it to rise.
Attached beneath the balloon is a radiosonde containing sensors and a radio transmitter.
As the balloon climbs, atmospheric pressure decreases and the surrounding air becomes thinner. The gas inside the balloon consequently expands, causing the balloon to become progressively larger.
During its ascent, the radiosonde continuously collects atmospheric measurements and transmits them back to equipment on the ground.
Eventually, the balloon expands beyond its limits and bursts. The radiosonde then falls back toward Earth, generally using a parachute to slow its descent.
A complete flight can provide meteorologists with a vertical profile of the atmosphere extending from near the surface into the stratosphere.
What Does a Weather Balloon Measure?
Weather balloons help meteorologists determine how atmospheric conditions change with altitude.
The radiosonde carried by the balloon typically measures several important variables, including:
- Temperature – how air temperature changes at different elevations.
- Humidity – the amount of moisture present in the atmosphere.
- Atmospheric pressure – how air pressure decreases as the balloon rises.
- Wind speed – calculated by tracking the balloon’s movement through the atmosphere.
- Wind direction – determined from changes in the balloon’s position during its flight.
Together, these observations create what is essentially a vertical snapshot of the atmosphere.
Surface weather stations can tell meteorologists what is happening near the ground. Weather balloons provide valuable information about what is happening thousands of metres above it.
What Is a Radiosonde?
A radiosonde is the small instrument package carried underneath a weather balloon.
Although the balloon is the most visible part of the system, the radiosonde is responsible for collecting most of the meteorological data.
Its sensors measure atmospheric conditions as it travels upward, while a radio transmitter sends the observations to a receiving station.
The movement of a radiosonde can also be tracked to determine winds at different altitudes.
Weather balloons and radiosondes are therefore closely related but are not the same thing: the weather balloon provides the lift, while the radiosonde performs the measurements.
How High Do Weather Balloons Go?
Weather balloons commonly reach the stratosphere, often climbing to approximately 30 to 35 kilometres above the Earth’s surface before bursting.
The exact altitude varies depending on the balloon, the amount of gas used, atmospheric conditions, and the equipment being carried.
This means a weather balloon can travel far above the altitude where commercial passenger aircraft normally fly.
As the balloon climbs, decreasing atmospheric pressure allows the gas inside it to expand dramatically. A balloon that appears relatively small at launch can become many times larger before finally bursting.
Why Do Weather Balloons Burst?
Weather balloons burst because atmospheric pressure decreases with altitude.
When the balloon rises, there is progressively less pressure from the surrounding atmosphere pushing against it. The gas inside the balloon expands as a result.
The balloon’s flexible material stretches to accommodate this expansion, but it can only stretch so far.
Eventually, the balloon reaches its physical limit and ruptures.
The attached radiosonde then begins descending toward the surface, typically with a parachute designed to reduce its speed.
Why Are Weather Balloons Important for Weather Forecasting?
Weather balloons allow meteorologists to observe the atmosphere vertically rather than relying entirely on conditions measured at the surface.
This is particularly important because weather develops throughout the atmosphere.
For example, conditions several kilometres above the ground can influence whether precipitation falls as rain, freezing rain, ice pellets, or snow. Changes in temperature and wind with altitude can also help meteorologists assess atmospheric stability and the potential for thunderstorms and other significant weather.
Weather balloon observations are also fed into numerical weather prediction models. These computer models use enormous amounts of atmospheric data to estimate how weather systems will develop and move.
Accurate observations of the atmosphere provide models with a better representation of existing conditions from which to begin their forecasts.
How Do Weather Balloons Help Predict Snow?
Weather balloon observations can be particularly useful when forecasting winter precipitation.
The temperature at ground level doesn’t always reveal what type of precipitation will reach the surface. Meteorologists need to understand temperatures through a much deeper section of the atmosphere.
A weather balloon can reveal layers of above-freezing and below-freezing air at different elevations.
For example, snowflakes may form high in the atmosphere but encounter a layer of warmer air while falling. Depending on the depth and temperature of subsequent layers, the precipitation reaching the surface could instead become rain, freezing rain, or ice pellets.
These vertical temperature profiles are therefore valuable when meteorologists are determining precipitation type during winter storms.
When Are Weather Balloons Launched?
Weather balloons are launched regularly from observation stations around the world.
Many upper-air observation stations coordinate their launches around internationally standardized observation times. This allows meteorological agencies around the world to collect atmospheric observations at approximately the same time.
Additional balloon launches may sometimes be conducted when more detailed atmospheric information is required, such as for research or significant weather events.
What Happens to a Weather Balloon After It Bursts?
Once the balloon bursts, the radiosonde and remaining equipment begin falling back toward Earth.
A small parachute generally slows the descent.
Depending on winds at different altitudes, the equipment can land a considerable distance from where the balloon was originally launched. It may come down in a field, forest, body of water, or another location along its flight path.
Some radiosondes include instructions explaining what to do if the equipment is found.
The balloon itself is generally not recovered because it breaks apart when it bursts.
Weather Balloons vs. Weather Satellites
Weather balloons and weather satellites both collect atmospheric information, but they serve different purposes.
Satellites can continuously observe enormous portions of the Earth’s surface and atmosphere. They are particularly valuable for tracking clouds, storms, moisture, temperatures, and large-scale weather systems.
Weather balloons provide detailed in-situ measurements as they physically travel through the atmosphere.
Rather than replacing one another, satellites, weather balloons, radar, surface weather stations, aircraft observations, and other observing systems work together to give meteorologists a more complete picture of the atmosphere.
Frequently Asked Questions
Yes. Despite major advances in satellites, radar, aircraft observations, and other technologies, weather balloons remain an important source of upper-atmosphere observations used by meteorologists and forecast models.
Weather balloons commonly reach approximately 30 to 35 kilometres above the Earth’s surface, although the exact altitude depends on the balloon and atmospheric conditions.
A weather balloon typically carries a radiosonde containing sensors and a radio transmitter. A parachute may also be included to slow the equipment’s descent after the balloon bursts.
Weather balloons are generally filled with helium or hydrogen. Both gases are less dense than the surrounding air and provide the lift needed for the balloon to ascend.
Weather balloons depend on buoyancy in the atmosphere to rise. As they climb, the surrounding atmospheric pressure decreases and the gas inside the balloon expands. The balloon eventually stretches beyond its physical limits and bursts long before reaching space.
The weather balloon provides the lift needed to carry equipment through the atmosphere. The radiosonde is the instrument attached to the balloon that measures and transmits atmospheric data.
