Weird Curved Lines

Ok so here's the thing. This morning, at about 7:00am when I took the dog out, I saw these lines in the snow. They were thin, and they would go straight for a while then curve, then pick up somewhere else, and do the same thing. For a visual reference, it looks probably like if you took an ice skate and drove it through snow, but magically, because there were no footprints at all around them. They were in my backyard and side yard and in the alley outback as well. I thought maybe someone had been riding a bicycle through, but there were no tread marks. So weird. It creeps me out. Then there were half circle almost brush marks on the sidewalk to my back porch. Of course I couldn't take pictures because by the time I got home, the snow had melted. But what was it!! How did this happen? Is this the snow version of crop circles? Maybe alien  ice skates made them!