What is the Difference Between Partly Cloudy and Mostly Sunny?

The difference between "partly cloudy" and "mostly sunny" lies in the amount of cloud coverage in the sky. According to the National Weather Service (NWS), both terms describe the same amount of cloud cover, which is between 3/8 and 5/8 of the sky. However, the terms can be used differently depending on the time of day:

• Mostly Sunny: This term is used during the day to indicate that the sky is more clear than cloudy, with 1/8 to 3/8 coverage of clouds.
• Partly Cloudy: This term is used to describe the same amount of cloud coverage as "mostly sunny," but it can be used both during the day and at night. It may feel slightly cooler than "mostly sunny" due to the increased cloud cover.

In summary, the main difference between "partly cloudy" and "mostly sunny" is the time of day when the terms are used and the nuances of their meanings. At night, a "partly cloudy" sky is considered less cloudy than a "partly sunny" day with the same amount of cloud cover. However, both terms essentially describe the same amount of cloud cover in the sky.

Comparative Table: Partly Cloudy vs Mostly Sunny

The difference between "partly cloudy" and "mostly sunny" can be subtle, but they generally refer to slightly different weather conditions. Here's a table summarizing the differences:

The National Weather Service defines partly sunny and partly cloudy as essentially the same, with the caveat that "partly sunny" is not used at night. However, some forecasters use these terms differently because the word "partly" is somewhat vague, so it's not always clear-cut. Both "partly sunny" and "partly cloudy" generally indicate that there is some degree of cloud cover, but the actual amount of sunshine and cloud coverage may vary depending on the specific weather conditions.