What’s the difference between ‘Partly Sunny’ & ‘Partly Cloudy’?

This week’s weather question is: Which describes more cloud cover: a partly sunny or partly cloudy day?

This is actually a trick question because partly sunny and partly cloudy describe the exact same amount of cloud cover…which is 3/8th to 5/8th cloud cover – or close to 40 to 60 percent.

The only difference is…partly sunny is used to describe cloud cover during the day and partly cloudy at night.

It’s the same reason why we say ‘sunny’ during the day instead of ‘clear’. Although sunny and clear describe the same amount of cloud cover – which is 12.5 percent or less – ‘sunny’ is used during the day and ‘clear’ at night.

Here’s a chart of what percentage or fraction the National Weather Service uses to describe cloud cover:

SUNNY (day) = CLEAR (night):                                 1/8th or less (12.5% or less)

MOSTLY SUNNY (day) = MOSTLY CLEAR (night):    1/8th to 3/8th (12.5% – 37.5%)

PARTLY SUNNY (day) = PARTLY CLOUDY (night):    3/8th – 5/8th (37.5% – 62.5%)

MOSTLY CLOUDY = MOSTLY CLOUDY:                  5/8th – 7/8th (62.5% – 87.5%)

CLOUDY = CLOUDY:                                               7/8th+ (87.5% – 100%)

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