What are those things? They're called snow rollers, formed when wind and snow conditions are just right. Phil Plaitt, creator of the Bad Astronomy blog, explains it all.
In his book Death from the Skies, Plaitt explains different ways the world could end. They include an asteroid impact like the one that did in the dinosaurs 65 million years ago, a poisonous atmosphere, and several others. It sounds scary, but Plaitt presents the science behind it all, and notes the very low probabilities of each deadly scenario.
If you like science blogs, Phil Plaitt's Bad Astronomy blog is a good one to add to your list.
(I learned something about adding these Amazon links: write the text first, then add the link, otherwise any attempt to start a new paragraph beside the link results in the cursor jumping to a point below the link, leaving empty space beside it.)