evidence: At some point in the spring, usually around early to mid May, the monsoon weather in the Indian Ocean pushes north over the sub-continent and this in turn pushes the high winds away to the north of Everest. This is the "weather window" that climbers use to find calmer weather at the summit. There is a similar situation caused by the impending arrival of winter that occurs in late October/early November, but this "window" is more unstable, darker and colder, so very few expeditions try to climb Everest in the post-monsoon (autumn) season. [...] Everest basecamp is very different. There are four seasons in the Khumbu, although summer is sometimes referred to as the monsoon. They are what you’d expect for the most part. Winter is very cold and it snows often. Spring is beautiful and sunny, but almost every afternoon it clouds up and sometimes a dusting of snow falls. Summer (monsoon) is warm and wet. At Everest basecamp (EBC) there are many storms and they can drop huge amounts of snow. In the autumn, the monsoon storms end and sunny warm days like spring appear until the crispy coldness creeps back into the air, the days shorten and winter rolls in again.