It is very difficult to find good studies of the climate of the Andes, especially given the lack of data and the fact that the Andean observing network has declined in quality over the past few decades. Nevertheless, using data from the early and mid 1970s, Maximiliano Viale and Mario Nuñez have a really nice paper on wintertime precipitation in the subtropical central Andes (30–37 S) in the latest Journal of Hydrometeorology. Some of South America's most famous ski resorts lie in this latitude belt, including Portillo, Valle Nevado, and Las Leñas.
One of the nicer figures in the paper presents a series of transects of mean winter precipitation across the Andes from north to south. Subfigure (b) is representative of the area along the main highway between Chile and Argentina, including Portillo. Note how precipitation is maximized on the windward slopes and not along the Andean crest, which is common in very high mountain ranges like the Sierra Nevada and European Alps.
|Source: Viale and Nuñez (2011)|
There a number of other great nuggets on Andean climate in the paper, but I'll leave it to you to find the rest.