mPing for iOS (free) is a unique weather app from the University of Oklahoma. The 'Ping' stands for Precipitation Identification Near the Ground. mPing is designed so that volunteers like you can make observations to crowdsource data to improve the next generation of weather radar.
Radar doesn't work very close to the ground, and most weather sensors near the ground are at airports. That leaves a lot of geography without radar coverage. The idea is that reports from observers streaming in will improve the algorithms used in weather predictions and reports.