Winter hiking and climbing take special preparation.
You must be prepared for extremes of cold, wind, snow and even rain and thaws. Skis or snowshoes are almost always needed. Even if there isn't much snow at the start of your trip, sudden storms can quickly appear and the amount of snow may increase as you climb and gain elevation. For above-treeline trips, an ice axe and crampons are necessities.
Winter hazards
Before striking out in winter, it's essential to be experienced with summer hiking and camping. A minor injury can become life-threatening in the harsh winter environment. Be sure that someone knows your trip plans.
Be prepared for the extremes in temperature and conditions with the proper gear and clothing. Hypothermia is a hazard year-round, but is especially dangerous in winter.
Snow cover may make route finding difficult, so know how to navigate with a map and compass.
Early thaws with their attendant racing waters, engorged streams and mud, can make negotiating trails and streams difficult and even dangerous.
Avalanches and ice or rock falls
Are winter hazards. The constant warming by winter sun with attendent snow melt combined with freezing nights slowly moves rocks which eventually tumble down the mountain. Everyone in your group should have a good knowledge of avalanche safety. Education and training are critical, so each member of your group should take an avalanche safety course.
Heed the warningsthey could save your life.
Avalanche Safety Basics
Most avalanche accidents are caused by slab avalanches which are triggered by the victim or a member of the victim's party. However, any avalanche may cause injury or death and even small slides may be dangerous.
Always practice safe route-finding skills and be aware of changing conditions. Learn how to use, and always carry, avalanche beacons, probles and shovels. You must be able to carry out a self-rescue in the event of a burial as time is critical. If you must go for help, it is generally considered too late. Learn to recognize avalanche terrain and understand snow stability evaluation techniques to help minimize your risk.
Read more about avalanche safety here.
No matter what the current avalanche danger there are avalanche safe areas in the mountains. Seek out the information needed to locate these areas and make informed decisions.
Avalanche Basics Tutorial - How To Save A Life - This is an excellent tutorial on basic avalanche safety provided on the Forest Service National Avalanche Center website.