NORTH CAROLINA -- Ever wonder what the difference is between mostly sunny and partly cloudy? Mostly cloudy & partly sunny? Well, if you have you're not alone. 

  • There's little difference between certain cloud coverage forecast terms
  • Certain terms are even "interchangeable" and might even come down to a need for a more optimistic vs. pessimistic feel
  • For example, if it's been cloudy and rainy for days on end, a forecaster may choose to use "partly sunny" instead of "mostly cloudy"

It's a question I hear often. And to be honest, there's little difference between certain cloud coverage forecast terms. Some may even say it's simply a matter of "semantics". 

Certain terms are even "interchangeable" and might even come down to a need for a more optimistic vs. pessimistic feel. 

For example, if it's been cloudy and rainy for days on end, a forecaster may choose to use "partly sunny" instead of "mostly cloudy".  Or, if you're in the midst of a heat wave, "partly cloudy" could make it feel a little cooler than "mostly sunny".

Bottom line, a typically breakdown involves breaking up cloud coverage by tenths (percentage) and looks something like this:

  • 0-10%  Sunny/Clear
  • 10-20% Fair
  • 20-30% Mostly sunny
  • 30-60% Partly cloudy
  • 60-70% Partly sunny
  • 70-90% Mostly cloudy
  • 90-100% Overcast