Abstract: Detection of wet and icy surface conditions on the surface of a pathway is accomplished using a block of electrically insulative material embedded in the pathway with its top surface flush with the surface of the pathway and exposed to atmospheric precipitation. A sensor electrode is encapsulated in the block and is positioned a predetermined distance beneath the top surface of the block so that an accumulation of atmospheric precipitation on the top surface affects the capacitance and conductance between the sensor electrode and the pathway. Provision is made for detecting the presence of impurities such as salt on the block's top surface. A time-varying electrical current is supplied to the sensor electrode at at least two different predetermined frequencies. The apparatus is relatively sensitive to impurities on the block's surface at one of the predetermined frequencies and is relatively insensitive to said impurities at the second predetermined frequency.