The top of Mt. Everest is engulfed by the jet stream for a major part of the year, making climbing near impossible due to high winds and extreme sub zero temperatures. It is only when the winds die down in May, that we have a so-called ‘Summit Window’, when conditions are safe enough for climbers to try and reach the summit. The other reason that climbers make summit attempts primarily in May is to avoid the harsh winter snows and summer monsoon rains.