What should Chance of Rain mean?

I am using the DarkSky API to get the local weather forecast.

Here are some different statistics for the probability of rain:

1. They say the chance of rain today is 85%.
2. The average probability of precipitation over the next 24 hours is 1%
3. The sum of the probabilities of precipitation over the next 24 hours is 21%.
4. The maximum probability of precipitation over the next 24 hours is 4%.

Here is a bar graph showing the probabilities (rounded decimals, not percents). Showing this to the user is not an option:

I can only show one statistic, so which of these do you think would make the most sense to users? Would you use a different statistic altogether?