Why am I 'pushed out' of a thermal?

[Aerosoft Team [Inactive Account] 51558]

The thermals have are not static columns of air that move up but have a gradient (so  maximum lift at the center and less and less if you go away from the center). When you enter a thermal it is likely that one wing is closer to the center then the opposite wing, so that wing will have more lift, will rise and will turn your aircraft away from the center of the thermal. 

 

So you can actually feel if there is more list, right or left of your aircraft!