A question which bothered me for some time, which I don't know how to address:

Every day, my weatherman gives a percentage chance of rain (let's assume its calculated to 9000 digits and he has never repeated a number). Every subsequent day, it either rains or does not rain.

I have years of data - pct chance vs rain or not. *Given this weatherman's history*, if he says tonight that tomorrow's chance of rain is X, then what's my best guess as to what the chance of rain really is?