The hard rime observations at the meteorological observatory of the Geophysical Institute of the Czechosl. Acad. Sci. on Milešovka (cone-shaped mountain, ф=50°33′ N, λ=13°58′ E,h=837 m, relative height about surrounding country cca 450 m) are regarded as representative for the medium heights above sea level in Bohemia. Hard rime occurs on an average 65 days a year, the hard-rime period lasting approximately 160 days (beginning around 7·11, end around 14·4). Table I gives the average numbers of days with soft rime, hard rime, glaze, fog and low cloudiness, the basis of which is below the level of the mountain peak. Table II gives the average yearly number of cases of hard rime of different duration (in hours). The mean temperature at which hard rime occurs is −3·7°C (the corresponding deviation from the normal is −1·0° C). The prevailing wind force during hard rime is 4–7 deg. Beaufort, the prevailing directions from ESE over S and W to NW. The frequency distribution of the direction and force of the wind during hard rime is given in Tab. V. Figure 1 shows the approximate probability of the existence of hard rime for different synoptic types (according to the classification in [3]) and finally Fig. 2 represents the dependence of the occurrence of hard rime on the circulationally significant changes in atmospheric pressure.