This is one of my pet peeves. There is ALWAYS a 50% chance of rain. Either it will, or ot won't.
Seriously, I think expressing it in percentage of probability is CYA for the weatherguessers. They just change the percentages to make it less obvious that they have no more idea than the man on the street what the weather will be.
"<insert percentage> chance of rain today."
If it rains: "See? I predicted there was a x% chance of rain."
If it doesn't rain: "See? I told you there was
only a x% chance of rain.
I don't fault anyone for not being able to forecast the weather.
I can't forecast the weather myself; but I don't collect a paycheck for pretending that I can, like weatherguessers do.