We've seen some deaths recently in the SGV mountains. This article is full of great advice including this last paragraph:
When you have the tools, skills, and experience, you can have an absolute blast exploring the mountains during the winter. However, if you’re feeling unprepared or uneasy in the terrain, turn back. If you forgot a crucial piece of equipment at home, turn back. If you are hiking in difficult terrain with someone who is not prepared, turn back. If you are comfortable with the ascent, but worry that you will not be able to descend, turn back. If your gut tells you to turn back, turn back. The trails and mountains will always be there – and you want to make sure you’ll be here to enjoy them the next time around.