Wind Lift Sailplane turns away from ridge when turning around Wind weaker near ground at a 45° angle, so that a quick egress away from the ridge is  possible should lift not be contacted.  Thermal sink can turn the glider upside down, a phenomenon  known as upset. A thermal may appear anywhere. When it  appears from the opposite side of the ridge, it has strong  energy. When flying in strong conditions (winds and  thermals), fly with extra speed for positive control of the  glider. DO NOT fly on the ridge crest or below the ridge on  the downwind side.  [Figure 10-19] NOTE: When approaching the ridge from downwind,  approach the ridge at a diagonal. If excess sink is encountered,  this method allows a quick turn away from the ridge.  [Figure 10-18] While flying along the ridge, a crab angle is necessary to  avoid drifting too close to the ridge or, if gliding above the  ridge, to avoid drifting over the top into the leeside downdraft.  For the new glider pilot, crabbing along the ridge may be a  strange sensation, and it is easy to become uncoordinated  while trying to point the nose along the ridge. This is both  10-11 Figure 10-15.  Ridge wind flow.