Dear Tom,
What is the difference between the terms “partly cloudy” and “partly sunny” in weather forecasts?
—Randall Mix, Round Lake
Dear Randall,
It is important that weather forecasts contain terms that are used accurately and equally important that those terms are correctly understood by the public. In weather forecasts, “partly cloudy” and “mostly sunny” refer to cloudiness that covers two tenths to five tenths of the sky; “mostly cloudy” and “partly sunny” refer to cloudiness that covers six tenths to nine tenths of the sky; “sunny” and “clear” refer to cloud cover between zero and one tenth of clouds, and “overcast” to a completely cloud-covered sky; “cloudy” to a sky at least nine tenths cloud covered. However, the definitions of these terms are not absolutely rigid.