If you’ve lived in tropical or even temperate climates all of your life, Everest may not be for you. During the optimal months for climbing – late spring – the daytime temperature can hover around 27 degrees (F) at base camp on a nice day. At the summit it may be around 0 degrees (F), but that’s not counting wind chill which can bring it to 65 below. Wind chill at base camp in May can make it feel about 6 degrees. In winter – you don’t want to be there anyway – the average summit temp with wind chill is 90 below zero.
So, if it’s just below freezing on a nice spring or early summer day at base camp, you can expect it to be around 0 at night. Not great sleeping weather – and one of many factors being studied by the Mayo physiologists.