I had another strange dream a while ago probably 1 maybe 2 years ago. Any ideas on this one?

When the dream starts I am in my bedroom watching television on a winter day, when I here a voice calling from outside. I stick my head out the window, when there I see my own sister. I see her laying on the grass which is partially white because of some leftover snow, with her clothes off, for they are thrown all over the grass. She is laying on her back, to where she is showing herself full-frontal. The dream does apply graphic detail, including vulva and breasts. But I doubt it was what she really looked like nude. But back to the dream, I disappear into my bedroom, for I am at that point heading outside to greet her but when I make it outside she is gone. Her, clothes, every sign of her. That is when I wake up. Can anyone interpret this strange dream?