Partly Cloudy...Partly Sunny...Mostly Stoopit

What part of the word 'partly' is so hard to understand?

The National Weather Circus sez 'partly cloudy' and 'partly sunny' are the same animal. Opaque clouds covering 3/10 - 6/10 of the sky. 'Sunny' is used during the day and 'cloudy' is used at night. Vanilla is as vanilla does.

Other meteorologists say "partly sunny means a mixture of sun and clouds is expected, but more sun than clouds. Partly cloudy also means a mixture of sun and clouds is expected, but more clouds than sun."

'Partly sunny' or 'partly cloudy' is "...a mixture of clouds and sun." OK. No problem with that part.

Now consider the following...
The forecast can call for a 'sunny'...'mostly sunny'...or 'partly sunny' sky. If 'partly sunny' means 'more sun than clouds'...does that mean ‘partly sunny’ is sunnier than ‘mostly sunny?

Or how about this...
The forecast can call for a 'cloudy'...'mostly cloudy'...or 'partly cloudy' sky. If 'partly cloudy' means 'more clouds than sun'...does that mean ‘partly cloudy’ is cloudier than ‘mostly cloudy?’

What stoopit comes up with this 'partly sunny is the same as partly cloudy' and 'partly is more than mostly' stuff...anyway?