With $2 million in funding behind it, the Sunshine app hit the iOS App Store on Wednesday. Sunshine promises to disrupt weather forecasting by using crowd-sourced data and providing custom point forecasts. Sadly, that promise will fall flat.

First, I’m pretty wary of weather companies that don’t have a meteorologist on staff. If Sunshine has one, they’re doing a good job of hiding that fact. It’s not that amateurs can’t be good forecasters, but the atmosphere is more complicated than it is often given credit for. The Sunshine team seems to know just enough to say things that sound reasonable but aren’t really. For example, this quote from CEO Katerina Stroponiati.

The more users we have, with phones offering up sensor data and users submitting weather reports, the more accurate we will get. Like an almanac.

Except that almanacs aren’t accurate. Then there’s this quote from their first Medium post.

The reason weather forecasts are inaccurate and imprecise is because traditional weather companies use satellites that can only see the big picture while weather stations are few and far between.

That’s fairly accurate (though it oversimplifies), but they point to a particularly noteworthy busted blizzard forecast as an example of the inaccuracy of traditional forecasts. Snowfall can be impacted greatly by small differences, but blizzards are fairly large-scale systems, and I’m skeptical that Sunshine would have done any better, especially considering that it has no “experience” outside of the Bay Area.

It sounds like Sunshine’s approach is basically a statistical model. That is a valid and often valuable forecast tool, but it has its limits. Sunshine claims a 36% improvement over “weather incumbents” in its trial period (where’s the published study?), but that involved only 200 testers in the San Francisco area. While definite microclimates exist in that region, it’s not exactly known for wild changes in weather. I doubt such an improvement could be sustained across a wider area.

Sunshine relies on crowdsourced reports and the pressure sensor in new iPhones to collect data. Unlike many other parameters, reasonably accurate pressure measurements are not sensitive to placement. A large, dense network of pressure sensors would be of considerable benefit to forecasters, provided the data is made available. However, wind, temperature, and humidity measurements — both at the surface and aloft — are important as well. This is particularly true for severe weather events.\

Crowdsourcing weather observations is nothing new. Projects like CoCoRaHS and mPing have been collecting weather data from the general public for years. The Weather Underground app has crowdsourced observations, and Weather Underground — along with other sites like Weatherbug — has developed a network of privately-owned weather observation stations across the country. The challenge, as it will be with Sunshine’s reports, lies in quality assurance and making the data available to the numerical weahther prediction models.

I hope Sunshine does well. I hope it makes a valuable contribution to the science of weather forecasting. I hope it gets people asking their Congressional delegation why we can’t fund denser surface and upper-air observations. I just don’t expect it will have much of an impact on its own.