Everest’s hostile microclimate
The biggest unknown on Everest is the weather. With extreme altitude comes extreme weather – and extreme unpredictability. And on top of that, Everest is so large that its gravitational pull is significant enough to create its own microclimate. 

The secret of tackling Everest – either on land or above it – is timing. For 250 days each year Everest is pounded by hurricane-force jet-stream winds that hit the upper faces at up to 200mph – violent, deafening winds that blow climbers off the mountain and that would literally crush a paraglider. But twice a year, first in May, when the warm monsoon air arrives in the Himalayas from the Bay of Bengal, and again in September when the monsoon leaves, warm air hits the mountains and lifts the jet-stream winds high over Everest’s summit, each time creating a short, critical calm weather window. 

These weather windows open for only a few days, but when they do they bring relative quiet to the summit. The winds drop to as little as 5mph leaving the mountain’s vault open. Being prepared for these weather windows and being in the correct position to exploit them is of utmost importance. GKN Mission Everest will be advised on this by liaising live with climbers on Everest about when to go and when to stay, essential for getting the timing right. The team's lives will effectively be in their hands.

The climbers on Everest will in turn get most of their meteorological input from Bracknell weather station, the world's leader in extreme meteorology at altitude. But, ultimately, the last 5% of judgement is based on the experience and instinct of the team and the climbers on Everest.

There is more detailed weather information to be found in the Event section of this site.