Abstract: A probe is fixed to a vertically displaceable rack. Under the probe is a reference plate freely exposed to snowfall. The probe is periodically lowered toward the reference plate and stopped when it encounters either the plate or a layer of snow which has fallen on the plate. With the aid of a light barrier and a perforated disk, electrical signals dependent upon the distance travelled by the probe are generated and transmitted to an evaluating device. This device calculates, on the basis of the signals received, the difference between the aforementioned distance travelled and the distance from the reference plate to the probe in its uppermost position. This difference corresponds to the thickness of the deposit of snow on the plate. For subsequent measurements, a new reference value corresponding to the surface of the snow already lying on the plate can be used for the calculation. Hence there is no need for clearing the plate of snow after each alarm signal.