The velocity of propagating sound signals in air depends significantly on the meteorological parameters wind velocity and temperature along the propagation path. The temperature influence is independent of the propagation direction of the sound wave: The warmer the air the faster the signals propagate. In contrast, airflow causes a directional change of sound velocity. A sound signal which propagates downwind is faster than in motionless air, whereas a sound signal which propagates in upwind direction is slower. These properties are used to draw conclusions about meteorological parameters from measurements of sound velocities.