Jargon - Partly Cloudy vs. Mostly Sunny

The age-old question..

What's the difference between Mostly Cloudy and Partly Sunny?

Basically, partly one thing vs. mostly another?

:D
 
Mostly cloudy and partly sunny are the same thing... The difference is, partly sunny is used during the day, and the term mostly cloudy was meant for night (though mostly cloudy can be used in the day). Both imply a 7/10-9/10 coverage of clouds.

Same goes for partly cloudy and mostly sunny.
 
Definitions:
Clear Skies: Skies are clear when no clouds or obscurations are observed or detected from the point of observation.

Cloudy: When the predominant/average sky condition is covered completely by opaque (not transparent) clouds. In other words, 8 octants of the sky is covered by opaque clouds.

Fair: It is usually used at night to describe less than 3/8 opaque clouds, no precipitation, no extremes of visibility, temperature or winds. It describes generally pleasant weather conditions.

Mostly Clear: When the predominant/average sky condition is covered 1/8 to 2/8 with opaque (not transparent) clouds. Called Mostly Sunny if it is during the day.

Mostly Cloudy: When the predominant/average sky condition is covered by more than half, but not completely covered by opaque (not transparent) clouds. In other words, 5/8 to 7/8 of the sky is covered by opaque clouds. Same as Considerable Cloudiness.

Mostly Sunny: When the predominant/average sky condition is covered 1/8 to 2/8 with opaque (not transparent) clouds. Same as Mostly Clear.

Partly Cloudy: When the predominant/average sky condition is covered 3/8 to 4/8 with opaque (not transparent) clouds. Same as Partly Sunny.

Partly Sunny: When the predominant/average sky condition is covered 3/8 to 4/8 with opaque (not transparent) clouds. Same as Partly Cloudy.

Sunny: When there are no opaque (not transparent) clouds. Same as Clear.
Sky Conditions
Sky condition
The predominant or average sky cover for the forecast period is also given. This percentage of the sky is the amount covered by opaque clouds, the type that do not allow other clouds, or blue sky to be visible through or above them. The descriptive terms for sky conditions are:

Term / Average sky cover
Cloudy 90-100%
Mostly cloudy 70-80%
Partly cloudy or 30-60%
Partly sunny
Mostly clear or 10-30%
Mostly sunny
Clear or sunny 0-10%
Fair Less than 40% cloud cover, no precipitation, and no weather extremes
Source: National Weather Service

Mike
 
Ok, so I was wrong... LOL

What Mike posts confuses me even more though... The definition of partly, according to how "partly cloudy" is described, is 3/8 to 4/8 coverage (in this case, that coverage is clouds, hence partly cloudy)

So if partly cloudy = 3/8 to 4/8 clouds, shouldn't partly sunny be 3/8 to 4/8 sun?

Partial sun = mostly clouds
Partial clouds = mostly sun

I guess I just take the terminology litterally, and these posts for that matter! :D...
 
When I did newspaper forecasting I always used partly sunny vs. partly cloudy as a way of splitting hairs on a 50% sun forecast. Whatever "sounded" most appropriate for the weather pattern is what I used.

Tim
 
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