Because the Andes block most of the moisture from the Pacific Ocean from coming in, causing it to release most of the precipitation on its western slopes, most of the province is dry, averaging less than a year. In the central parts of the province, some areas receive less than of precipitation a year. In the Andean part, precipitation increases towards the Chilean border and precipitation ranges from to over . A Mediterranean like precipitation pattern, similar to central Chile with dry summers and wet winters is found in the area between the Andean region to the west and the dry steppes to the east. Although precipitation can widely vary among the province, in all locations, precipitation is higher during the winter months. Thunderstorms are rare and occur exclusively during the summer.