"Valley-wind days" are characterized by synoptically undisturbed, clear-sky conditions, which lead to the formation of thermally-driven slope- and valley-wind circulations in mountain regions. A simple method is presented to identify these conditions in the Inn Valley, Austria, using ERA-Interim geopotential height fields and a clear-sky index, which is calculated from measurements of longwave incoming radiation, air temperature, and humidity at a single site on the valley floor. As the method is based on identifying weak synoptic-scale flows and clear skies, it can also be applied to the identification of ideal conditions for other thermally-driven circulations. The mean diurnal cycle of the valley-wind circulation on these days is briefly discussed.