How Dark Sky Works

What is Dark Sky?

An accurate short-term weather predictor. (By short-term: half or one hour.)

http://www.kickstarter.com/projects/jackadam/dark-sky-hyperlocal-weather-prediction-and-visuali?

And now here is a post about how it works:

http://blog.jackadam.net/2011/how-dark-sky-works/