If you've ever wondered what the difference between "partly cloudy" and "mostly sunny" is, this video has all the answers. In the video, Simon Whistler of the Today I Found Out YouTube channel goes over all the terms you might here if you watch the weather report on your local news channel. A lot of it comes down to opaque cloud cover (OCC) as established by the National Weather Service, or how much of the sky is covered by clouds you can't see through completely. "Sunny" means there is less than 25 per cent OCC, or "clear" if it's less than five per cent.
In Australia "clear" is defined as "virtually cloud free". "Mostly sunny" and "partly cloudy" mean the OCC is between 26 per cent and 50 per cent, and they're interchangeable. "Partly sunny" and "mostly cloudy" usually mean the OCC is somewhere between 51 per cent and 69 per cent, but "mostly cloudy" can also be used at up to 87 per cent OCC. At OCC of 88 per cent or above, the sky is considered "cloudy" or "overcast".
You'll also learn about the probability of precipitation (POP), or the likelihood of rain. For example, terms like "chance of rain" or "likely" are used as expressions of uncertainty. If you hear those, they think it could rain, maybe. The same goes for terms like "isolated" or "scattered", but it's assumed the rain, if it comes, won't affect the entire area. Whistler also covers terms relating to labelling temperature, wind chill and how humidity affects the heat index in the video, so be sure to watch through to the end.