It’s one thing to survive in the wilderness in mild weather. You might be cold, dehydrated, and hungry, but you’ll probably make it at least a few days.
Surviving in cold weather is a completely different beast though. Without adequate gear, knowledge, and skills, you can succumb to the cold or any other number of dangers quickly.
You can dig directly into a mound of snow to create a cave for sleeping. If the snow isn’t deep enough to provide a stable structure for a roof, you can put pine boughs over the top.
Layering actually means wearing clothes that keep you dry, trap heat, and protect you from the elements. A good set of layers will keep you equally comfortable in 50°F and 15°F temperatures.
Cornices are very dangerous because the can look like part of the mountain. But, when you walk on it, the cornice can collapse and send you falling to your death.