A particle-based simulation of cloud formation. Water vapour rises from warm ground, cools adiabatically with altitude, and condenses at the dew point, forming cumulus, stratus and cumulonimbus clouds.
The thermodynamics of cloud formation: warm moist air rises, expands and cools. When temperature hits the dew point, water vapour condenses on nuclei. Convective strength determines cloud type — gentle lifting for stratus, vigorous for cumulonimbus.
Choose a cloud preset (cumulus, stratus, cumulonimbus) or adjust temperature and humidity manually. Watch particles rise, cool and condense at the Lifting Condensation Level.
Bolton's equation gives dew point to within 0.1°C. The lifting condensation level rises by roughly 125 m for every 1°C difference between air temperature and dew point.
This simulation shows how cloud droplets form when moist air rises and cools. Up to 500 particles represent water vapour lifting from warm ground; their altitude is converted to temperature using a constant lapse rate. Where the parcel temperature falls to the dew point, vapour condenses into white droplets. The dashed line marks the Lifting Condensation Level (LCL), the height at which cloud forms.
You set the ground temperature T₀ (10–40°C), relative humidity (10–100%), the environmental lapse rate (4–12°C/km) and horizontal wind. From these the model derives a dew point and an LCL using the Magnus and Bolton approximations, then classifies the result as cumulus, stratus, stratocumulus or cumulonimbus. Understanding this process explains everyday weather, convective storms and aviation cloud forecasting.
What is cloud formation?
Cloud formation is the process by which invisible water vapour in rising air condenses into visible droplets. As a moist air parcel ascends it expands and cools; once it reaches its dew point, vapour condenses onto tiny aerosol nuclei and a cloud appears. This simulation models that process with particles rising from warm ground.
What is the Lifting Condensation Level (LCL)?
The LCL is the altitude at which a rising air parcel becomes saturated and cloud begins to form. It is shown here as the dashed blue line. The model estimates it as roughly (T₀ minus dew point) divided by 8, times 1000 metres, so drier air gives a higher cloud base.
How is the dew point calculated?
The simulation uses a simple Magnus-style approximation: dew point equals T₀ minus (100 minus relative humidity) divided by 5. So at 60% humidity and 25°C the dew point is about 17°C. Higher humidity brings the dew point closer to the air temperature, lowering the cloud base.
Temp T₀ sets the surface temperature, humidity sets how much moisture the air holds, lapse rate sets how fast temperature drops with height, and wind shears the particles sideways. Together they change the dew point, the LCL height and the resulting cloud type shown in the info panels.
The lapse rate is the rate at which air temperature falls with altitude, expressed in °C per kilometre. The default 6.5°C/km is the standard atmospheric average. Steeper lapse rates (here up to 12°C/km) make the atmosphere more unstable, favouring tall convective clouds like cumulonimbus.
The model classifies clouds from the inputs: a steep lapse rate of 8 or more with humidity of 75% or above gives cumulonimbus; high humidity of 80% or more with a shallow lapse rate gives stratus; high humidity with a low cloud base gives stratocumulus; otherwise it returns cumulus. The presets simply load representative values.
It is a simplified educational model. The dew point and LCL formulas are recognised approximations accurate to roughly a degree, and the lapse-rate cooling is realistic. However it ignores latent heat release, the moist adiabatic lapse rate, mixing and real droplet microphysics, so it shows the principles rather than exact meteorological values.
Below the LCL particles behave as buoyant vapour and rise. Above it they are treated as condensed droplets: they gain slight downward velocity and drift toward the centre of their altitude band, mimicking how cloud droplets gather and how heavier ones eventually settle or fall as precipitation.
Lower humidity means the dew point is much colder than the surface temperature, so the air must rise further to cool enough to saturate. Since the LCL depends on the gap between temperature and dew point, a large gap pushes the cloud base higher. This is why deserts often have high, sparse clouds.
Pilots and air-traffic forecasters use the LCL to predict cloud bases, glider pilots use convective lapse rates to find thermals, and meteorologists use humidity and instability to anticipate thunderstorms. The same thermodynamics underlies weather models, fog forecasting and even cooling-tower plume behaviour.