I’ve long considered forecast.io to be the fully featured, grown up, desktop version of the Dark Sky iOS app. It’s always done more than notifications and short-term predictions but was just as accurate and easy to use.
That’s probably because they are made by the same people and use the same data. As of today they are sensibly going to operate under the same name: Dark Sky.
I’m currently reading The Weather Experiment by Peter Moore, a terrific account of human efforts to understand and predict the weather. Highly recommended.