Although most thunderstorm cells complete their life cycle in 30 minutes, thunderstorm weather may persist at a specific location for 6 to 12 hrs or longer. explain why

The thunderstorm is more likely to remain in the area for longer periods of time if mountains are present. The air is forced up the mountain, and the instability and moisture remain, meaning the thunderstorm persists. 

The convection currents that exist between the cold and hot air due to density differences may also remain, which means that the thunderstorm weather will also remain.