It's been about two years since we wrote about Google's Secret Weather API, when we pegged the number of official weather APIs at just 8. The directory has certainly expanded since that time, but growing at an even faster rate is the weather category. We currently list 37 weather APIs, more than four times the number in 2010.
There are some well known names in here, such as the U.S. National Weather Service API and Weather Channel API. These have been in the directory for some time, probably because weather is something people have cared about long before APIs came about, so it makes sense to make this stream of data available to developers.
There are three weather APIs added in the last two years that have mashups in our directory, showing increased interest with developers: World Weather Online API, Weather Central API and AccuWeather API. The latter was used to create the Weather Zombie site, a truly unique way to receive the current conditions.
In addition to new entrants, there was an update from at least one of the old stalwarts. The Weather Underground API made a bunch of changes, including a transparent pricing plan. It was an especially developer-friendly approach since Weather Underground replaced XML with JSON.
One reason weather APIs may be so popular is that many types of applications can take advantage of them. The weather is an added dimension that, like location in general, can provide extra context. There's even a potential to combine the real world with video games. Can you imagine Mario Kart loading in your current weather? Watch out for the icy roads in the winter and you better hope your kart doesn't overheat in the summer.
Being such a useful bit of information, it's strange that Google, the company that tasked itself with organizing the world's information, doesn't seem to want to take its weather API out of unofficial mode. Nearly four years ago the company line was "for gadget use only."