Since October 1995, a daily forecast of the UV index, as the irradiance of the biologically effective ultraviolet radiation, for the next day is published for Austria, Europe, and world wide. The Austrian forecast model as well as the input parameters are described. By connecting the UV index with the sensitivity of the photobiological skin types, a recommendation is given to select an appropriate sun protection factor of a sunscreen to avoid overexposure of the skin. The validation of the Austrian forecast model is done by measurements of the biologically effective ultraviolet radiation collected between July 1996 and July 1998 at Vienna (48 ¿N, 16 ¿E), Austria. The forecast quality is evaluated by comparing the Austrian model with two statistical models used in Canada and the Netherlands. By using the underestimation of the UV index as criteria in the sense of radiation protection, the Austrian model shows a 12% underestimation over the whole year. ¿ 2000 American Geophysical Union