[dscb]

"tell me when it's going to rain tommorrow"

Would the service tell you what time it would be raining/not raining the next day?

Or would it alert you the first day that the weather told it that it would be raining the day after?

[eksith]

This would depend which weather data provider is being used. On my AccuWeather app, there's a graph showing the temps and whether it will rain etc... by the hour, but I'm not sure how accurate it is.