The BBC is retracing the footsteps of the 1953 British Everest expedition as they made their way up to base camp in preparation for the first successful assault on the mountain's summit. BBC correspondent Jane Hughes, now at base camp, is keeping a diary of her journey.
Days 12-13: Waiting in line.
We're experiencing a lot of personal firsts on this trip.
There is a lot of frustration at base camp
My latest was to wake up to find that my contact lenses had frozen inside their case, and that my toothpaste was rock solid.
There was frost on the inside as well as the outside of the tent. It was the beginning of a bad day.
The altitude was telling badly on me as I made my way to the mess tent, and our group leader took one look at me, and sent me straight back to my sleeping bag.
That's where I spent the rest of the day, feeling nauseous, and incapable of doing much more than lifting my head to take acclimatisation medication.
Altitude sickness was a constant concern of the 1953 Everest expedition, and I'm beginning to understand why.
The team spent weeks accustoming their bodies to the lack of oxygen, climbing high during the day and then spending their nights at lower altitude, allowing themselves to adjust to the altitude before making their way to a new camp higher up the mountain.
We're now at 5,300 meters above sea level, with just half the oxygen we're used to breathing.
I've only been suffering the more minor symptoms of ascending too fast. Acute Mountain Sickness, as it's called, can result in fluid on the lungs or swelling of the brain, either of which can rapidly be fatal.
Thankfully, I'm feeling more able to function today, and have had my first real experience of life in base camp.
All attention today has been focussed on the attempts by 150 or so climbers and as many sherpas to reach the summit.
No one this year has yet made it to top of Everest by the southern route pioneered by Sir Edmund Hillary and Tenzing Norgay, and the tension is building, as the window of opportunity for climbing narrows.
Last night, the sky was clear, and the stars were shining startlingly brightly.
It seemed the ideal opportunity, and the first teams set out from camp 4, high on the mountain, soon after dark; with so many people heading for the summit, they wanted to get ahead of the queues.
We were up just after dawn and standing in an expedition communications tent to hear the news. And it was disappointing.
Their team got as far as the "balcony", two or three hours' walk from the summit, and then decided the relentless, battering wind was so extreme, they could go no further.
Another team from South Africa had an even greater disappointment - they got to within 350 meters of the summit before being driven back by the gales.
No one from the south side made it to the summit, although a few succeeded from the north side.
The teams are now hunkering down in their tents waiting for the next opportunity.
They may go again tonight, but the weather is deteriorating, and if that attempt fails, many will be forced by lack of oxygen and food to descend to base camp.
The weather is making climbing in the region very difficult this year
The closer we get to the end of the climbing season, the more it looks as if no one at all will make it to the top of Everest by the route pioneered by the 53 expedition on this anniversary year.
And if there is another opportunity, so many people are likely to go for it at once, there's potential for disaster. The mood here at base camp as we watch the weather forecasts and wait is grim.