Rain is measured in mm/h. It can change significantly in minutes and it can differ significantly in a 100m area. Therefore, a rain sensor is the only meaningful way of detecting current rain.
The next best thing are the condition or the precipitation per hour.
Condition can be accurate to half an hour, but itās often much worst.
In all cases, it is good to know how your favorite weather service works. Does it show the weather of the closest weather station or does it calculate an average for your exact location based on several weather relations.
A animated weather radar image can also be useful and would be my recommendation for must UI related things.