Avo's don't like a frost. They can withstand light frost but a few frosts in one season will burn off the leaves and possibly kill the tree.
I don't think snow comes into it. They'd have to be planted in a pot and moved inside or under cover in winter. Even a cold wind can burn/kill the tree. They are a tropical plant. I live in a subtropical area and have some problems with avos in winter.

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The secret is the soil.