Pilvet

Pilvet (Finnish for clouds) are visible masses of condensed water vapor or ice crystals suspended in the Earth's atmosphere. They form when moist air rises, expands, and cools to the dew point, causing water vapor to condense on nuclei. Clouds vary in altitude, thickness, and shape, and they are a central element of weather and climate because they reflect sunlight and trap infrared radiation.

Clouds are commonly grouped by altitude and by vertical development. Low clouds include stratus and stratocumulus (up to about 2,000 meters); middle clouds include altostratus and altocumulus (2,000–6,000 meters); high clouds include cirrus, cirrostratus, and cirrocumulus (above 6,000 meters); clouds that grow vertically, such as cumulus and cumulonimbus, can span several levels and often produce precipitation. Common forms observed include cumulus (puffy), stratus (layered), cirrus (wispy), and cumulonimbus (thundercloud).

Clouds influence weather and climate not only through precipitation but also by their radiative properties: thin high clouds trap some heat while reflecting sunlight; thick low clouds tend to reflect more solar radiation. The balance of cloud formation and dissipation affects regional weather patterns and the energy budget of the planet. Fog is essentially a surface-level cloud.

Monitoring pilvet is a core activity of meteorology. Observations come from ground stations, weather balloons, radars, lidars, and satellites, while model simulations use cloud physics to forecast precipitation and storm development.