Silly Weather

This is our weather forecast for the next seven days in Portland. I have one question... what is the difference between "Partly Sunny" and "Partly Cloudy"? Doesn't that really say the same thing? There will be blue skies and some clouds on Monday, blue skies and less clouds on Tuesday, on Wednesday we are back to blue skies and some clouds, Thursday blue skies and some clouds, but on Friday and Saturday look out, we've got some clouds and blue skies.

Notice that on Monday and Wednesday it calls for "Partly Sunny" however the clouds in the graphic on Monday look bigger than the clouds on Wednesday. And the clouds on the "Partly Sunny" days are the same as the clouds on the "Partly Cloudy" days. I'm so confused.

Is there a Meteorologist Thesaurus out there helping these guys?