Traveling in winter times requires big fat bulk of warm attire - traveling in winter for Tibet requires SERIOUS big fat bulk of warm attire. November through April is a real test for survival skills - temperatures drop to -2 degrees C (low 20s F) and the altitude adds discomfort. If you absolutely have to go during these months - stock up on warm socks, mittens and long johns. Does not sound glamorous - I know - but gets you in all the fun activities and lets you stay ALIVE. Breezy May and October are a perfect chance to get out your wind-proof jackets and Timberland boots you've been dying to use. With a slight chance of rains it might also be a good idea to pack an umbrella or a hat. June through September is the busiest traveling season. Get ready to stand in lines and pay extra for anything that you want to do - however the weather is warm and sunny and levels of oxygen are higher. Pack hiking attire - shorts and Ts, and throw in a couple of sweaters - nights get chilly.