Remember also that the warmest part of the day is usually the worst for avalanches and acclimatising is very important, the higher you go the lighter the air is and there is less oxygen. It can cause many problems including heart attacks due to a high heart rate and your body creating more red blood cells and it becomes thicker therefore slower and stickier and there is more chance of it clotting. Also altitude sickness is quite common.
Acclimatise to your environment slowly and prepare for it. You have to have a high level of fitness and understanding to operate in this environment.
Hypothermia and frostbite mentioned earlier by Jack - it's very important to keep warm weather clothing and spares. Sleeping clothes that are not wet from sweating. Do not wear too many layers as you will sweat too much and the sweat will cool and lower your temperature.
"The pressure on our bodies is about the same as ten metres of sea water pressing down on us all the time. At sea level, because air is compressible, the weight of all that air above us compresses the air around us, making it denser. As you go up a mountain, the air becomes less compressed and is therefore thinner.
The important effect of this decrease in pressure is this: in a given volume of air, there are fewer molecules present. This is really just another way of saying that the pressure is lower (this is called Boyle's law). The percentage of those molecules that are oxygen is exactly the same: 21%. The problem is that there are fewer molecules of everything present, including oxygen." - http://www.altitude.org/why_less_oxygen.php