This is neat, and even though you've never heard about it, it's become quite popular among yarn crafters. Sharon McDermott crocheted a row on an afghan every day. The color of yarn each day was determined by the day's high temperature. After a year, she has a full blanket with an archive of the local weather conditions!
You can get instructions from knitting or crocheting blogs, or at YouTube. While the colors are up to the creator, and the blankets will vary widely by latitude, I wonder how a blanket made now will vary from a blanket made in the same home ten years from now. -via Boing Boing