A few times a winter hoar frost forms on the steps of Morningside Park. When it forms the frost is usually an inch or two wide and three or four inches long. The frost formed last week so I took a picture to use on Gothamist. I even predicted there would be another occurence this morning!
Surprisingly, my prediction came true. In the extreme. I've never seen the frost so extensive on these stairs. It forms on them when moist, supercooled air flows out of the cracks between the steps and touches the cold granite, freezing instantly. Look up 'hoar frost' via Google or Flickr, or look at these pictures to fine examples much more beautiful than these.