I’m surprised how many places in the world measure rain in percentage chance. Must be a metropolitan concept. Here in Denmark, weather reports estimate mm/hr - the amount of rain. Maybe it’s our agricultural inheritance?

If you're deciding whether to dress and prepare for rain you're more curious about whether it will rain or not than the amount.

https://weather-sense.leftium.com shows both mm/hr and percentage chance.

I've noticed there is a correlation, but having both is useful:

- Often there is a percentage chance, but the mm/hr is 0. At these times, it could rain but will probably be very light.

- Less common, but sometimes there is 0% chance, but a non-zero mm/hr.

The two things are not strictly related, you could have 30% chance of heavy rain, or 90% chance of light rain. Both are needed and many apps have both.

Most places I look at report both probability and give a measurement prediction.

So it would be like "60% chance of rain after 2pm, total amount less than 1/10th of an inch"

mm/hr is more useful for areas that get lots of rain. When I was living in Seattle, chance of rain was meaningless but mm/hr made the difference between being able to do an outside activity or not. In California, chance of rain makes sense because it rains very little.