I found out recently that those percentages actually mean 80% of the local AREA would have rain and 20% would not. Meaning if there is a chance of rain in your town at all it’s likely raining somewhere even if it’s just a tiny drop or two.

So if you don’t want to get wet at all bring an umbrella if the chance is over 0%.

Source: was talking to a meteorologist about this exact thing.

Well rain chance is a compound probability it's the probability that it will or will not rain multiplied by the percent of land hit with rain. Like if 50% of an area will be hit and there's an 80% chance it will rain the number the weather Channel will give you is 40%

Chance of rain is calculated based on two things: Meteorologists' educated guess on the chance of rain, multiplied by the area that will receive rain, in the event it does rain.

https://www.discovery.com/science/chance-of-rain

Not to mention Xcom.

Missing a 90% shot 3 times is so dam annoying.

In gen 1 that would be only Swift, Bide and self-targeting status moves because every 100% accuracy move can miss due to a bug (1/256). Fun fact: you would actually be able to beat the game with these 2 moves because Bide, in gen 1 only, bypasses Ghost's immunity to Normal moves.

'drop rates' are the same thing. 10% chance doesn't mean you will see it drop if you run a mission or defeat that boss ten times.