Fog Warning  signals are graded into three levels: yellow, orange and red.

            a）Fog Warning  Yellow Signal

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Meaning: the visibility may be less than 500m in 12 hours caused by heavy fog. Or, the visibility is between 200 m and 500 m, and is likely to continue.

             b）Fog Warning  Orange Signal

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Meaning: The visibility may be less than 200 m in 6 hours caused by very heavy fog.  Or, the visibility is between 20 m and 50 m, and is likely to continue.

              c）Fog Warning  Red Signal

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Meaning:  The visibility may be  less than 50 m in 2 hours caused by extreme heavy fog.  Or, the visibility is less than 50 m, and is likely to continue.