Partly cloudy, partly sunny, mostly cloudy, partly sunny…what’s the difference?!?
Here is an excerpt from a recent email I got:"You guys use the terms partly sunny, partly cloudy, mostly sunny, mostly cloudy. Isn't mostly sunny and partly cloudy the same thing? The same with mostly cloudy and partly sunny? Is there a specific definition for each of these four terms?"
This was such a good question that I felt compelled to share the answer with all.
Simply put, there are specific definitions for each term, although in all honesty, I sometimes tweak these definitions for the purpose of what I want to emphasize on a given day. For example, partly cloudy and partly sunny both mean we will have between 3/8 and 5/8 cloud cover that day, but I've found that when I say partly cloudy, people tend to picture more of a cloudy day. When I say partly sunny which also means 3/8-5/8 cloud cover, people tend to picture a mainly sunny day. So, if I think it will be a sunny day, but maybe a little on the cloudy side at times, I'll say partly sunny to emphasize that much of the day will be sunny. If I picture a mainly cloudy day with periods of sunshine mixed in, I'll go ahead and say partly cloudy so people working on their summer tans won't get their hopes too high.
Some hard core scientists cringe at this philosophy, but in the world of TV where most watching are not scientists, perceived accuracy is just as, if not more important to me than mathematical accuracy. Scientifically, partly sunny is used for 3/8-5/8 cloud cover in the day time and partly cloudy is used to describe the same conditions at night.
That said, here are the scientific definitions for the various amounts of cloud cover:
Sunny skies- less than 1/8 cloud cover expected.
Mostly sunny- 1/8-2/8 cloud cover expected.
Mostly clear- 1/8-2/8 cloud cover expected at night.
Partly sunny- 3/8-5/8 cloud cover when it's daylight.
Partly cloudy- 3/8-5/8 cloud cover expected at night.
Mostly cloudy- 6/8-7/8 cloud cover expected.
Cloudy- 7/8 or more cloud cover expected.
Confused yet? Now you see why I sometimes tweak the definitions a bit to paint the right picture. Afterall, who really goes outside, snaps a photo of the sky, and analyzes it to see what fraction of cloud cover there is? I don't. In my eyes, a mathematically correct forecast is no good to me if everyone thinks I was wrong because I painted the wrong picture of what to expect today.
Got a question you'd like to see answered, post it here and maybe I'll blog about it!
Posted by on 05/30 at 06:58 AM
