the climate of central chile is of temperate mediterranean type, with the amount of rainfall increasing considerably and progressively from north to south. in the santiago area, the average monthly temperatures are about 19.5 °c in the summer months of january and february and 7.5 °c in the winter months of june and july. the average monthly precipitation is no more than a trace in january and february and 69.7 millimeters in june and july. by contrast, in concepción the average monthly temperatures are somewhat lower in the summer at 17.6 °c but higher in the winter at 9.3 °c, and the amount of rain is much greater. in the summer, concepción receives an average of twenty millimeters of rain per month; in june and july, the city is pounded by an average of 253 millimeters per month. the numerous rivers greatly increase their flow as a result of the winter rains and the spring melting of the andean snows, and they contract considerably in the summer. the combination of abundant snow in the andes and relatively moderate winter temperatures creates excellent conditions for alpine skiing. areas around the bío-bío river, historically called la frontera corresponds to southern limit of the mediterranean climate, with typical mediterranean fruits such as avocado, citrus, olives and grapes being cultivated north of it and oat, wheat, apples and potatoes to the south. this more or less drastic transition is caused by the split of the westerlies at these latitudes (~37° s) into one branch going to the southeast and another to the northeast, to this it is necessary to add the north-south lowering of the chilean coast range which reduced the rain shadow effect.