Partly Cloudy? Mostly Sunny?

E and his dad had an argument today on whether “partly cloudy” and “mostly sunny” meant the same things or different things.

I told E he had to look it up on the net when we got home.

He asked what would happen if he was right? I said he’d get to say his dad was wrong.

When we got home, he half-heartedly looked it up and couldn’t find anything. R also got on the net and started looking and eventually went to the National Weather Service’s website. I got on the net and googled ‘”mostly sunny” “partly cloudy” definitions.’

These are some of the quotes from the top sites.

Ask the Meteorologist says:

The specific definition for “partly cloudy” is 30-70 percent sky covered by clouds. Partly sunny is similar to “partly cloudy” but is used more frequently during the day to emphasize daytime sunshine. I find that when people hear “partly cloudy” they think more clouds than sun and when they hear “partly sunny” more sun than clouds. “Mostly sunny” is less than 30 percent covered by clouds and “mostly cloudy” more than 70 percent covered by clouds. When the sky is “overcast” more than 90 percent of the sky is covered by clouds.

Kevin Wyatt at the Roanoake Times wrote:

“Partly cloudy and partly sunny are essentially the same thing,” said David Wert, meteorologist-in-chief at the National Weather Service office in Blacksburg. “Both are used for conditions when the average amount of opaque cloud cover ranges from 45 percent to 75 percent. We usually use ‘partly sunny’ for daytime conditions, and ‘partly cloudy’ for nighttime conditions under these situations. It wouldn’t make too much sense to use ‘partly sunny’ for a nighttime condition.”

The Weather Notebook, a nationally syndicated radio show about weather says:

“Clear,” or “sunny” skiesthose two terms are synonomouscontains up to 10 percent opaque sky cover, while mostly clear or mostly sunny falls between 10 to 30 percent. “Partly sunny” and “partly cloudy” have the same definition in the Weather Service glossary a 30 to 60 percent cover. So, if you thought that “partly sunny meant a brighter day than “partly cloudy,” sorry. Mostly cloudy,” also known as “considerable cloudiness,” is 60 to 90 percent. Anything over that, and it’s just plain “cloudy.”

The National Weather Service’s glossary says:

Partly Cloudy: When the predominant/average sky condition is covered 3/8 to 4/8 with opaque (not transparent) clouds. Same as Partly Sunny.
Mostly Sunny: Same as Mostly Clear, except only applicable during daylight hours; when the predominant/average sky condition is covered 1/8 to 2/8 with opaque (not transparent) clouds.

So there you have it. Partly Sunny and Partly Cloudy mean the same thing.

But Mostly Sunny and Partly Cloudy do not.

E, in the wisdom of teenhood, insists that this is ridiculous.