Sky cover circles
The circle at the centre of a station plot shows how much of the sky is covered by cloud: empty for clear, half filled for half covered, and solid for overcast. A circle with an X means the sky could not be seen.
How to read it
NOAA’s Weather Prediction Center says the amount the station circle is filled in reflects the approximate amount of sky covered by cloud. NOAA’s JetStream school lists ten symbols, for zero to eight eighths of the sky (oktas) plus “sky obscured”, which is used when fog, dust or something else at the surface hides the sky. The University of Wisconsin–Madison’s notes group the eighths into clear, few (1/8 to 2/8), scattered (3/8 to 4/8), broken (5/8 to 7/8) and overcast (8/8). The Met Office describes cloud cover in the same way, by shading the centre of the station circle.
Also searched as: clear sky symbol, cloud cover symbol, filled circle on a weather map, half filled circle, oktas, overcast symbol.
These pages describe what each symbol on a weather chart means. They are not forecasts or warnings: for those, the national weather service for the area is the source.
The circles by eighths
Clear No cloud. 1/8 A single line through the circle. 2/8 A quarter filled. 4/8 Half filled. 6/8 Three quarters filled. 7/8 Filled except for a gap down the middle. 8/8 Filled solid: overcast. Sky obscured An X in the circle: the sky is hidden by fog, dust or the like.
Eighths or fourths
NOAA and the WMO report cloud in eighths. Iowa State University’s surface map help page describes its station circles in fourths, so a simpler map may show fewer steps. The WMO’s code 9 is “sky obscured, or cloud amount cannot be estimated”.
Look-alikes
An empty circle with a second circle round it is not sky cover but calm wind, on JetStream’s Wind barb chart.
Read next
- Next in Weather map symbolsRain symbolDots are the rain symbol on a weather map. One dot is light intermittent rain and two side by side light continuous rain; more dots mean heavier rain.
- The same shape in Asian flagsFlag of KazakhstanKazakhstan’s flag is sky blue with a golden sun and its rays in the centre, a soaring golden steppe eagle beneath it, and a vertical band of golden national ornament along the pole. The President’s website says the blue stands for a pure sky, peace and prosperity, and its single colour for the country’s unity; the sun for wealth, abundance and life; and the eagle for the state’s power, sovereignty and independence.
More weather map symbols
The same shape elsewhere
Browse symbols drawn with circles.
Sources
- Station Model Information for Weather Observations, Sample station plot, NOAA National Weather Service, Weather Prediction Center, Sky cover
- JetStream Max: Surface Weather Plot Symbols, JetStream, the NWS online weather school, NOAA National Weather Service, Sky Cover Symbols
- Reading the surface station model, Online Weather supplemental information, 9 February 1999, by Edward J. Hopkins, University of Wisconsin–Madison, Department of Atmospheric and Oceanic Sciences, Sky cover convention
- Manual on the Global Data-processing and Forecasting System, Appendix II-4: Graphical representation of data, analyses and forecasts, WMO-No. 485, Appendix II-4 (as circulated to IPET-DRMM-III, Beijing 2015), World Meteorological Organization, 2.1 N Total cloud cover
- Understanding weather charts, Key Stage 4 lesson plan, Crown Copyright, Met Office (hosted by MetLink, Royal Meteorological Society), Part C: Cloud cover
- Surface Map Help Page, PALS severe weather forecasting help pages, Iowa State University, Department of Agronomy, 1) Station Data Plot
Researched, edited and approved by Rory Hansen before publishing. Last reviewed October 9, 2026. How we research
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