Because they do not think that there is a problem with themselves. Until they hit bottom, they usually will not seek help. They become paranoid and think we are trying to tell them what to do.
I can see where his mind was at when you mentioned the snow....he "assumed" that you were going to ask him to come over and stay. The less you ask him about staying over, the better. Let him make the decisions about what he needs to do. They want to be in control and when you suggest something, he thinks you are taking control over him and his decisions.
Make a list of what needs to be done before the storm hits. I don't know exactly where you live, but there will be gusty winds tomorrow afternoon, which gives the potential for the power to go out. Fill out containers with water. After the children take baths this evening, fill the tub up just in case. Get your flashlights and lanterns out. You might even want to bake up some extras this evening to have on hand that can be ate on the cold side. Show this man that you can handle this storm.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.