The Bolivian Service for Meteorology and Hydrology (SENAMHI) forecast continued cold weather in the Western, highlands of Bolivia until mid August.
http://www.paginasiete.bo/2011-07-26/Sociedad/Destacados/FRIO.aspx
So, if you intend to travel to Oruro, La Paz or beautiful Potosi, please bring warm clothes or buy here precious alpaca clothing from “Millma”, “Angora y Alpaca” “Fotrama” or “Casa Fisher” I can vouch for their quality!