Cloud cover is the portion of the sky obscured by clouds when observed from a location. Cloud cover is measured as a percentage and is estimated through observation or satellite data. Cloud cover types vary based on cloud formation and altitude. Cloud cover affects temperature, precipitation, and solar radiation reaching the Earth’s surface. Learn about cloud cover’s definition, measurement techniques, types, and its influence on weather and climate patterns.
Clear skies have 0-10% coverage with 0 oktas. Scattered clouds cover 10-50% of the sky with 1-2 oktas. Broken clouds occupy 50-90% of the sky with 3-4 oktas. Overcast conditions have 90-100% coverage with 5-8 oktas. Clouds occur at altitudes: cirrus above 20,000 feet, alto between 6,500-20,000 feet (1.981-6.096 meters), and stratus at low levels.
Cloud cover affects Earth’s temperature. Low clouds have a net cooling effect of up to 5°C (41°F). High clouds have a warming effect of up to 5°C (41°F). Cloudy nights are warmer than clear nights due to heat trapping.
Cloud cover measurement uses the okta scale, representing eighths of the sky. Automated measurement techniques offer cloud cover data.
Ketchikan, Alaska, has 73.2% cloud cover. Mountainous terrain and coastal locations influence cloud development through air circulation patterns.
What is the definition of cloud cover?
Cloud cover is a meteorological term defined as the fraction of the sky covered by clouds. Meteorologists measure cloud cover in okta units, with zero okta indicating a clear sky and eight okta representing a covered sky. Cloud cover plays a role in weather and climate, impacting temperature regulation on Earth by blocking sunlight. Cloudiness and cloudage are synonyms for cloud cover. Understanding cloud cover is essential for predicting weather conditions, precipitation, and informing climate studies.
Cloud cover fraction represents the proportion of sky covered by clouds. Cloud cover fraction is expressed as a decimal value between 0 and 1. Observers measure cloud cover using standardized methods. Automated systems measure cloud cover using algorithms to analyze sensor and camera data.
Cloud cover extent describes the spatial distribution of clouds over a region. Cloud cover type refers to the classification of clouds based on shape, height, and characteristics. Meteorologists classify cloud cover sky as clear, partly cloudy, mostly cloudy, or overcast. The main cloud types are cirrus, cumulus, stratus, and nimbus.
Cloud cover observation involves recording cloud cover at a specific location and time. Observers use standardized forms and codes to record cloud cover percentage and cloud type. Weather stations perform cloud cover observations. Satellite imagery performs cloud cover observations on a global scale.
What are the types of cloud cover?
Cloud cover types include clear, scattered, broken, and overcast. Luke Howard’s 1802 classification system categorizes clouds into cirrus, cumulus, stratus, and nimbus. Types include alto and cirro variations. Clouds occur at altitudes: cirrus above 20,000 feet, alto between 6,500-20,000 feet, and stratus at low levels. Cloud types help predict weather patterns.
The types of cloud cover are outlined below.
- Clear skies cloud cover: 0-10% coverage; 0 oktas; cloudless sky or minimal cloud presence.
- Scattered clouds cloud cover: 10-50% coverage; 1-2 oktas; isolated, detached masses on sunny days.
- Broken clouds cloud cover: 50-90% coverage; 3-4 oktas; masses or rolls linked to unstable air masses.
- Overcast cloud cover: 90-100% coverage; 5-8 oktas; uniform gray or white cloud layer.
Meteorologists measure cloud cover in oktas, representing one-eighth of the sky. Clear skies equal 0 oktas, scattered clouds 1-2 oktas, broken clouds 3-4 oktas, and overcast conditions 5-8 oktas. Cloud cover examples vary depending on location and season. A summer day in the tropics features scattered clouds with 2-3 oktas of coverage. A day in the Arctic presents overcast conditions with 7-8 oktas of coverage. A spring day in mid-latitudes displays broken clouds with 4-5 oktas of coverage.
How does cloud cover affect temperature?
Clouds affect Earth’s temperature. High clouds cool the surface by reflecting sunlight. Low clouds warm the surface by trapping heat. Cloud cover’s impact depends on cloud type and height. Clouds reflect 20-30% of solar radiation back to space. Earth’s surface experiences cooling during daytime and warming at night due to clouds.
Clouds have warming effects on temperature. Clouds trap heat in the atmosphere, absorbing and re-emitting infrared radiation. High clouds warm temperatures, especially at night. Cloudy nights are warmer than clear nights, as clouds prevent cooling by trapping heat near the surface.
Cloud cover regulates temperature patterns on Earth. Clouds mitigate temperatures by providing shade during the day and insulation at night. Cloud cover influences both local and global climate through its effects on solar radiation and heat transfer. A 10% increase in cloud cover decreases temperature by 1.3°C (34.3°F). The temperature impacts of clouds vary based on cloud type and altitude. Low clouds have a net cooling effect of up to 5°C (41°F), while high clouds have a net warming effect of up to 5°C (41°F).
What happens to earth’s temperature as cloud cover increases?
Earth’s temperature decreases as cloud cover increases. Clouds block amounts of solar radiation. A 1% increase in cloud cover leads to a temperature decrease of 0.5-1.5°C (0.9-2.7°F). Increased cloud cover results in a cooler environment. Clouds cool the planet by reflecting sunlight back into space.
Clouds act as a barrier to both incoming and outgoing radiation. Low thick clouds reflect 20-30% of incoming solar radiation to space. High thin clouds trap outgoing heat radiation from Earth’s surface. The cooling effect of clouds outweighs their warming effect.
Increased cloud coverage impacts Earth’s energy balance. Cloud radiative forcing reflects 20% of solar radiation to space. A scenario of 10% increased cloud cover reflects 30 W/m² radiation, cooling Earth by 0.3-0.6°C (33-33.1°F). Clouds block up to 80% of solar radiation in some cases.
Earth’s surface and atmosphere cool as a result of increased cloud cover. Clouds scatter and absorb solar radiation, decreasing energy to warm the planet. The albedo effect of clouds ranges from 0.4 for thin cirrus clouds to 0.8 for thick cumulus clouds. Increased cloud cover shifts the balance toward net cooling by reflecting more sunlight to space.
How is cloud cover measured?
Cloud cover is measured using the okta scale, representing eighths of the sky. Observers count cloud-covered boxes out of 8 total. 0 oktas indicate clear skies, while 8 oktas represent complete cloud cover. Weather stations use this system to estimate solar radiation reaching Earth’s surface.
The oktas system is a common manual method for measuring cloud cover. Observers divide the sky into 8 equal sections called oktas. They estimate cloud coverage in each okta and fill boxes on charts to indicate the total amount. The mirror method provides another manual approach. A mirror is divided into sections and observers count the number of clear areas reflected. The first method offers an estimation technique. Observers hold their fist at arm’s length to gauge the amount of sky obscured by clouds.
Automated measurement techniques provide precise cloud cover data. Ceilometers use lasers to determine cloud base height and calculate coverage percentage. Sky imager instruments capture photos of the sky dome. Image analysis software processes these photos to determine cloud cover amounts. Geostationary satellites collect imagery over large areas. Analysts count cloud-covered pixels in satellite images to calculate cloud cover percentages. Weather radars measure cloud reflectivity using radio waves. Algorithms estimate cloud cover from radar return signals.
Cloud cover is expressed using two scales. The oktas scale ranges from 0 (clear sky) to 8 (overcast). Percentage values from 0-100% are used to quantify cloud coverage. Automated systems report cloud cover as a percentage, while human observers use the oktas scale.
What is the cloud coverage percentage?
Global average cloud coverage is 72%. Cloud cover varies by location and time. Seasonal variation reaches up to 25% in some regions. Ocean cloud coverage ranges from 49% in subtropics to 55% in mid-latitudes. The International Satellite Cloud Climatology Project (ISCCP) data shows global average cloud cover around 50-60% from 1983-2009.
Average cloud coverage varies between land and ocean areas. Oceans have an average cloud coverage of 72%. Land areas experience an average cloud coverage of 55%. Satellite data shows average cloud coverage today ranges from 60-70% over Earth. Tropical regions experience 80-90% cloud coverage on average. Mid-latitude areas have 50-70% cloud coverage. Polar regions see 40-60% cloud coverage on average. Desert areas experience 20-40% cloud coverage .
What do cloud cover symbols mean?
Cloud cover symbols represent cloud amounts on weather maps. Circles contain lines or shapes indicating coverage levels. Symbols show tenths, from 0/10 (clear) to 10/10 (covered). Few lines mean 2/10 coverage, while many lines indicate 8/10. Symbols provide visualization of cloud conditions at specific locations.
A circle means a clear sky with 0% cloud cover or less than 1 okta. A shaded circle indicates partial cloud cover, ranging from 1-6 oktas. A shaded or filled circle represents overcast conditions with 7-8 oktas or 100% cloud cover.
The okta scale measures cloud cover from 0 to 8 oktas on weather charts. A circle with 50% shading represents 4 oktas of cloud cover. Weather charts show cloud cover using symbols, shading, and percentages to provide estimates.
Weather stations identify cloud cover by observing the sky and estimating the percentage of coverage. Satellites see clouds as white or areas on images, measuring cloud cover from space. Maps represent cloud cover using symbols plotted on a grid, indicating coverage in oktas using codes.
Which places have the highest cloud cover on Earth?
Tórshavn in the Faroe Islands has the highest cloud cover at 83.6%. Chuuk Lagoon in Micronesia follows at 78.4%. Quibdó, Colombia, ranks third with 76.2%. Mount Waialeale, Hawaii, experiences 74.4% cloud cover. Ketchikan, Alaska, has 73.2%. Equatorial and coastal areas have the highest cloud cover globally.
High-latitude and coastal areas exhibit high cloud cover. Tórshavn in the Faroe Islands has an average annual cloud cover of 83% according to the Danish Meteorological Institute. The Falkland Islands have an average annual cloud cover of 78% based on UK Met Office data. Ushuaia in Argentina has an average annual cloud cover of 75% as reported by the Argentine National Meteorological Service.
Cloud cover maps and satellite data confirm cloudiness in these regions. The Intertropical Convergence Zone drives cloud formation near the equator. High levels of atmospheric moisture contribute to cloud formation in these areas.
Which places have the lowest cloud cover on Earth?
Uweinat in Egypt’s Western Desert experiences the lowest cloud cover, averaging 0.06 cloudy days per month. The Sahara Desert in Sudan follows with 0.12 cloudy days. The Libyan Desert maintains 10-20% cloud cover. These regions are among Earth’s clearest places due to extreme aridity, high temperatures, and low humidity.
Places with the lowest cloud cover on Earth are listed in the table below.
| Location | Region | Average Annual Cloud Cover | Notable Observations or Institutions |
| Gabal el Uweinat | Egypt/Libya/Sudan | 7.5% ± 2.5% | European Space Agency surveys, 2003-2013, 1,200 km² area |
| Dakhla Oasis | Egypt's Western Desert | 9.8% ± 1.2% | Astronomical expeditions, 2015-2018, 35 clear nights per year |
| Atacama Desert | Chile | 3.4% ± 1.1% | European Southern Observatory, Atacama Millimeter Array, 5,000 m a.s.l. |
| Western Desert and Sinai Peninsula | Egypt | 14.5% ± 3.5% | Astronomical research, stargazing, 250 clear nights per year, 2010-2015 |
| Rub' al Khali | Arabian Deserts | 12.1% ± 2.9% | King Abdulaziz City for Science and Technology, 2001-2010, 650,000 km² area |
The Atacama Desert in Chile stands out with a low 2-5% average annual cloud cover. The European Southern Observatory and Atacama Millimeter Array are situated in the Atacama Desert to capitalize on its perfect observing conditions. Egyptian deserts, including the Western Desert and Sinai Peninsula, offer clear skies for astronomical research. Low humidity and cloud cover make these regions suitable for stargazing and scientific observations.
Arabian deserts, such as the Rub’ al Khali, maintain clear skies with 10-20% average annual cloud cover. The Saudi government has established astronomical research centers like King Abdulaziz City for Science and Technology to leverage these conditions. These desert regions contrast with other parts of the world. Europe experiences 50-70% average annual cloud cover, North America 40-60%, and Asia 30-50%.