About a year and a half ago, I was ready to leave the law school for the day, and so I packed up, glanced outside, and noticed a light drizzle. I ride my bike to and from work, about two miles from my home. I have no real problem being rained on, but if I could wait a few minutes and ride in mist or drizzle, I’d prefer it to riding in what might become a downpour. Glancing at the weather, you get something like this, which gives you a rough probability for rain for the “afternoon” or “evening.” Yes, weather.com does give forecasts in fifteen-minute increments, but I’ve never been a fan — having always been partial to the National Weather Service site and, especially in winter storm season, the forecast discussions.

I wanted an app that would quickly tell me what the chances were for rain, at different intensities, over the next half hour or so. An app that would quickly tell me whether to go home right now or wait it out a bit. I had this idea that you could scrape the NWS radar images, use an algorithm to detect the edges of the colored shapes that are the storms, and extrapolate to predict where the colored shapes would be over the next hour (maybe getting a little fancy by pulling in other data). While weather prediction is very, very hard and especially difficult to get right at particular places, perhaps it wouldn’t be so difficult to get reasonably accurate (for my purposes) forecasts for only an hour in the future.

Needless to say, I never made the app. But Adam Grossman and Jack Turner (no relation) had a similar idea and an absolutely terrific concept for implementing it. They raised money on kickstarter and have now shipped Dark Sky. It’s a fantastic application. Far better than the one I’d had in my head and just beautifully designed to do one kind of thing excellently.

On the iPhone, it comprises essentially two views. In one, you see text that tells you what the temperature and state of precipitation is right now and, below it, what will happen in the next hour. This view also shows a very clever graph. On the x-axis is the time, from now to an hour from now. On the y-axis is the level of precipitation, ranging continuously from none to low to medium to heavy. The yellow curve representing this wiggles to show uncertainty. The more it wiggles, the less confident you should be. Of course, this portrayal elides two distinct concerns: confidence that it will rain at all and heaviness of precipitation. But for the purposes for which you’ll use the thing, collapsing that into one nice graph is somehow perfect.

Just today, I was wondering whether it would rain while I was out for a run. I wanted to know whether it was likely to pour so hard that I needed a sandwich bag to encase my iPhone and whether I should encourage my father-in-law to go out for a walk. The app told me it would continue to rain lightly for a few minutes, not rain for about thirty, and then rain moderately to heavily after that for the rest of the hour. So I grabbed the sandwich bag, encouraged my father-in-law to walk into town (with an umbrella and having thought I could pick him up after the run if need be), and headed out. For the first few minutes, it drizzled lightly. It stopped for the next thirty minutes, and I was drenched for the last fifteen minutes. The app nailed it. Smells like the future.