cloudcover

Cloud cover, or cloudiness, is the fraction of the sky obscured by clouds at a given location and time. It is commonly expressed as a percentage or on the oktas scale, an eight-point scheme that estimates how much of the sky is cloud-covered. The scale runs from 0, meaning a completely clear sky, to 8, meaning an overcast sky.

Measurement and observation are carried out by ground-based human observers and by remote sensing. In meteorology, sky cover is reported in synoptic observations and aviation reports. The oktas scheme is still used in some contexts, while many weather services provide cloud fraction as a percentage. Meteorological uses are supplemented by satellite observations, which deliver broad-scale cloud cover data through instruments such as imaging radiometers.

Cloud cover results from atmospheric moisture, temperature structure, and vertical motion, and it varies with time of day, season, and weather systems. Lifting mechanisms such as fronts, convection, and orography, along with humidity and temperature gradients, determine the types and extent of cloud cover. Common cloud regimes range from scattered and broken cover to dense, widespread cloudiness, with different cloud types (cirrus, cumulus, stratus, nimbostratus) contributing to the overall fraction.

Impacts of cloud cover are broad. It moderates surface solar radiation and affects daylight levels, influencing energy balances, agriculture, and ecosystem activity. In weather forecasting and climate studies, cloud cover is a key variable for predicting precipitation, temperature, and radiation budgets. Satellite-based cloud-cover data are widely used for climate monitoring, weather prediction, and solar-energy planning.