The mountain's highest zone, over 2,000 metres, is snowcapped for about nine months (September to May). In some places the winds gather snow, 8-10 metres thick (anemosouria in Greek), while in some deep ravines the snow is maintained all over the year (everlasting snow). For this Olympus' alpine region, recordings have been made in the 1960s in the highest-altitude weather station in Greece, that was established on the summit of Aghios Antonios (2,815 m), providing a number of interesting data for the mountain's climate. The average temperature is −5 °C in winter and 10 °C in summer. The average annual precipitation heights vary from 149 cm at Prionia (1,100 m) to 170 cm at Aghios Antonios, about half of them rainfall and hailstorms in summer and the rest snowfall in winter. The weather may change several times in the same day. In summer rainfalls are frequent, commonly as evening thunderstorms, many times accompanied by hail and strong winds. However water springs over 2,000 metres are scarce and visitors should ensure that they have always water and of course the necessary clothing for any weather conditions.