Winter in the Himalaya is difficult for many reasons. Temperatures at base camp can plummet to minus 20 degrees Fahrenheit, and much lower farther up. Because of the cold, climbing at night is virtually impossible, and the days are short. The winds are much stronger and more persistent because of the jet stream, which blows almost constantly from December through the end of March. Tents are constantly being destroyed or blown away. The wind also strips away the snow, exposing rock and hard ice, making easier slopes more technical and time-consuming. Lower barometric pressure leads to less oxygen in the air. The combination of these factors makes for an exhausting, and generally miserable experience.