Storm receding, view from Base Camp (Photo: Adam Pease) Dust storm on "Broad Beach" approach to Base Camp (Photo: Eldon Boone)
Weather on Aconcagua is variable, but has a tendency, acording to mountain guides, to be on a cycle of roughly 10 days, with adverse weather often lasting 3 days followed by a week of decent weather. Apart from general patterns, weather moves in from the west, and the forecast for Santiago is often more indicative of what is to come to the mountain than the forecast for Mendoza.
January and February have the best weather, and are when most people attempt the climb. Rain is rare, (although it was frequent in late February 2006). The climb to base camp is generally mild or even hot and can be done in a t-shirt and shorts. However, during my Feb 2005 climb we had 50-60 mph wind gusts and stinging blown sand on the approach. The coldest night of the trip was in base camp (in three-season tents), with several inches of snow. During that time, people higher on the mountain were trapped in camps by high winds and zero-visibility conditions, and some lost their tents during the night, leaving people in very dangerous situations. Base camp normally has fresh water from a glacial stream, but it was frozen solid even during the day for about 36 hours.
Conditions at Berlin camp even in good weather are normally very cold, with temperatures at 0 degrees F when starting out for the summit before sunrise. Typical wind chill makes it much colder. Frostbite is a near constant danger unless one is properly equiped. On summit day the climber should have plastic double boots, layers of down and GoreTex, and ideally no exposed skin even on the face. The sun is a constant danger also, even on cloudy days. Nearly every climber suffers a sunburn on some little part of the face that is lacking sunscreen or cover. Don't underestimate this problem. A sunburn from reflection off of snow often catches people by surprise since a hat covers one from above, but not from reflected sun from below.
In 2006 weather prevented us from moving from Nido to Berlin camp. A "window" of forecast good weather the next day prompted us to attempt the summit from Nido. However, we started at 4:30am with a temperature that was already below 0 Farenheit, and strong winds and snow. The cold intensified, and the winds became dangerous as we ascended forcing us to abort the attempt just below Independencia. Continued snow forced us to descend further to Base Camp after a brief rest at Nido. We encountered waist-deep drifts on the decent. No one summitted that day or likely the next.
Because of the cold, climbers above base camp will have to melt snow for water. If you are doing the climb without guides you need to allow at least an hour each day and plenty of fuel for this chore. It takes a surprisingly long time.
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