If there is doubt about which way to turn, release all pressure on the stick and allow the ship to drift for just a moment to gain some idea of which direction to go. An uncontrolled sailplane will usually tend to drift awayfrom thermal lift – but the opposite may be true in shearlines… If after only a couple seconds you have already flown beyond it, the area of lift was probably too small anyway, and by not turning you will have saved altitude and time. Also, do not presume that turning is always necessary. On the luckiest days (streets, shears, etc.), you might be able to take full advantage of lift while simply porpoising on course, without needing to circle at all!
Several other qualifications relate to the initial thermal turn. When you find lift head-on and the wings remain level, you may feel a sequence of bumps as you proceed from the surrounding thermal sink into the stronger lift of the core. As air rushing out from the core creates a sudden increase of indicated airspeed, it might simultaneously raise your angle of attack and reduce the actual velocity of the moving sailplane. In other words, an indicated ‘speed-up’ could accompany an actual ‘slow-up’. A corresponding loss of control effectiveness will soon follow, but you can easily counter this with a slight pitch-over before initiating your thermal turn. (All of these are reasons why you should concentrate on physical perceptions and attitude of the sailplane more than the instruments!)
If there is reason to believe the thermal is exactly straight ahead and so narrow that a turn either way would move you out of it, turn to one side slightly before beginning to circle the other way, hopefully to ‘pre-center’ the thermal.