During a 4 days jeep trip through the bolivian altoplano, we arrived at Lagua Verde in the middle of a Bolivian winter blizzard. You couldn't see the lake, let alone the volcanos - it was just plane white. We came back up for a morning a few weeks later from the Chilian side and were rewarded with these perfect condidions - it was worth all those waits at border crossings for entry and exit stamps!