Weather Whys: The difference between partly cloudy and partly sunny

Weather Whys: The difference between partly cloudy and partly sunny

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One of the most common questions meteorologist get asked is, "What is the difference between partly cloudy and partly sunny?". Viewer Carolyn asked that question as part of the Weather Whys segment on the CBS 58 News at 7 on WMLW-The M. 

The answer is simple and yet complicated. It may be helpful to understand how we actually decide any type of cloud cover. Cloud cover is determined by staring at the sky and dividing it into eight equal parts. If 1/8 or less of the sky is covered with clouds it's Sunny, if 1/8 to 3/8 is covered with clouds it's Mostly Sunny, if 3/8 to 5/8 is covered with clouds it's partly cloudy, if 5/8 to 7/8 is covered with clouds it's Mostly Cloudy and if 7/8 to 8/8 are covered with clouds it's Cloudy. 

Notice that partly sunny is not mentioned in the above categories. According to the National Weather Service, partly cloudy and partly sunny mean the same thing and can be used interchangeably but that's not how all meteorologists think. Some use partly sunny only during the day and partly cloudy only at night. Others say partly cloudy has less clouds than partly sunny since if it is "partly" cloudy then the majority of the sky is cloudy. Others try to avoid both terms and instead say "a mix of sun and clouds."

Personally, I hardly ever use the term "partly sunny" which gets rid of the problem! 

Weather Whys is a segment by Meteorologist Justin Thompson-Gee that airs during the CBS 58 News on WMLW - The M from 7 a.m. to 8 a.m. The segment answers viewer weather questions, explains weather phenomena and reveals interesting weather stats. To submit your question reach out to Justin on Facebook, Twitter or by emailing him at JThompson-Gee@cbs58.com. 

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