Indeed, Dark Sky’s big innovation wasn’t simply that its map was gorgeous and user-friendly: The radar map was the forecast. Instead of pulling information about air pressure and humidity and temperature and calculating all of the messy variables that contribute to the weather—a multi-hundred-billion-dollars-a-year international enterprise of satellites, weather stations, balloons, buoys, and an army of scientists working in tandem around the world (see Blum’s book)—Dark Sky simply monitored changes to the shape, size, speed, and direction of shapes on a radar map and fast-forwarded those images. “It wasn’t meteorology,” Blum said. “It was just graphics practice.”
I certainly can't speak to the science here (although my tack in college had me take a few more upper level meteorology classes than you might expect), but Dark Sky has always been a bit of a weirdo. It wasn't always right for me, but it was shockingly accurate enough that it was my go-to for finding out when the rain was going to hit me. Extended forecasts? Eh, not as amazing, but being able to open the app, see that rain was 16 minutes away, and then have the rain start basically right on schedule is an awesome trick.
It's also a good time to remind everyone that almost all the weather data these private companies use for their apps is collected by a federal agency that gives the data away to the public. AccuWeather isn't out there doing this work, they're packaging up the data in a nice(ish) way, which provides its own value, but it's always good to recognize the things the government does that private companies use to get the credit (see also GPS).