Would your applications, mobile or otherwise, benefit users more if they provided weather data and weather forecasts? If so, check out the OpenWeatherMap.
The free OpenWeatherMap API provides weather data including the current weather, a weekly forecast (5 and 14 day) , and data on precipitation, wind, clouds, and more. The weather data is aggregated from global meteorological broadcast services and more than 40,000 independent weather stations.
All weather data can be obtained in JSON, XML or HTML format. Data can be search by city name, geographic coordinates or by city ID. Also, numerous languages are supported including Russian, Chinese, Italian, Spanish, German and many others.