cloudbase

Cloud base is the lowest altitude of a cloud layer as seen from the surface. It refers to the height at which a cloud begins in the vertical profile of the atmosphere and can apply to a single cloud or to the base of the lowest layer in a multi-layer deck. The term is widely used in meteorology and aviation to describe the vertical structure of cloudiness.

Measurement and estimation of cloud base rely on several methods. Ground-based instruments such as ceilometers estimate base height by detecting the bottom of the cloud using light or radar signals. Radiosondes provide vertical profiles of temperature and humidity that allow calculation of cloud-base height from the lifting condensation level. In routine observations, cloud base can also be estimated from visual ceiling readings and standardized observation codes.

The height of the cloud base depends on ambient temperature, humidity, and atmospheric stability. A common approximation relates cloud base to the lifting condensation level, with LCL ≈ 125 × (T − Td) in meters, where T is air temperature and Td is dew point in Celsius. Warmer, drier air tends to raise the cloud base or prevent cloud formation, while cooler, moister air lowers it. Orographic lifting and wind can also raise or lower cloud bases in the affected region.

Ranges vary by cloud type. Low clouds such as stratus, stratocumulus, and cumulus typically have bases from near the ground up to about 2,000 meters (6,500 feet) above ground. Higher-level clouds, like altostratus and cirrus, have bases well above 2,000 meters. Fog is a form of cloud whose base is at ground level. Cloud base is a key factor in aviation, weather forecasting, and climate studies.