Abstract: A signal balloon (2, 2') has an inflated configuration that is horizontally elongated with opposite tapered ends (4, 6, 4', 6'). The balloon (2, 2') is shaped and dimensioned to cause it to ascend in response to an increase in wind speed. The sidewalls of the balloon (2, 2') have light transmitting portions (10, 10') and reflective portions (12, 12'). A light (40, 40') is positioned inside the balloon (2, 2'). The light may be an electric lamp (40) connected to a power source (64) on the ground via an electrically conductive tether (34). The light (40') may also be the upper end of a fiber optic conductor tether (34') which has a lower end connected to a light source (92') on the ground. The balloon (2') is provided with pivotable lower and upper lift members (22', 24') which are connected to the tether (34') and pivot in response to changes in orientation of the tether (34') to increase the lift of the balloon (2') when the tether (34') inclines away from a vertical position.