Global Cloud Cover Maps

These maps are constructed using data acquired by the PATMOS -x program . Patmos-x collects satellite radiance measurements and uses complex algorithms to automatically detect clouds and infer their properties around the globe. Data collected are normally used for climatological studies, but this and other datasets have proved valuable for astronomical pursuits for over two decades.

Clouds are not always easily detected from satellites. In the tropics and over the bulk of the oceans they are the white things in the image. Over Canada in winter, the white stuff is frequently snow and ice. Temperature is not always much help, as clouds in winter can be warmer or colder or just like the white stuff on the ground. The same applies to mountains, where white bits in the image can also be snow or ice, even in summer. Nevertheless, there are other infrared wavelengths at which it is possible to separate cloud from ground and the combination of all information usually keeps the artifacts under control.

The data in these maps have a resolution of 1/2 degree in latitude and longitude. The cloud cover values are an average of available data, from 1 July 1982 through 2007, from both daytime and nightime satellite passes. Images on this site are composed from the afternoon ascending pass of the polar-orbiting satellites and corresponds to approximately 2 p.m. local time.

These maps should be used cautiously, as satellite-based cloud datasets have several known biases. Use them for comparative purposes, rather than as absolute values of cloudiness.

Global Afternoon Average Cloud Cover in Tenths
Month
Month
January
July
February
August
March
September
April
October
May
November
June
December

 

 

 

 

 

 

These images are not copyrighted and can be used freely.

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