TI Free allows glider pilots to quickly determine soaring conditions for the day by computing the Thermal Index. You can enter the airport identifier of your gliderport and TI Free will locate the nearest RAOB sounding station and high temperature for the day at that location. You can then see the computed Thermal Index, winds aloft, and cloud base estimate. Many pilots believe that the altitude where the TI value reaches -3 (or -1.67 Celsius) is the highest level of usable thermals.

As I glider pilot myself, when I wrote TI Free, I kept the following in mind
Ease of use: I wanted an app that would remember my settings, use the power of the iPhone to automatically update weather information, and quickly show me what I need to know
Accuracy: TI Free uses Virtual Temperature to compute Thermal Index in an effort to remove as much if the error as possible caused by the humid weather of summer.
Value: Flying is expensive enough already. TI Free is available at no cost; however, advertisements fund future development and work. Please support the advertisers.