A Temperature Scarf/Blanket/etc is a conceptual project -- different colours are assigned to temperature ranges in your local area (e.g. on a 11-15 degree day, you might knit a light blue row; on a 6-10 degree day, a dark blue row). At the end of a year, you'll have a record of the daily temperature in crafty form. The project can take any form you like, any pattern, any combination of colours. There are so many ways of going about this project that it's a bit daunting! Jillian's method of making a hexagon-shaped granny square every day is cute and wouldn't take too much work, but on the downside, there will be a lot of ends to weave in, and she has to make adjustments to plan for the fact that 365 squares won't fit neatly into a square afghan.
A straight granny stitch afghan. Picture Source
Several others that I've seen made scarves using double/circular knitting, which I've done before in making the Harry Potter scarf. I'm really drawn to this idea, as there isn't too much knitting to have to do each day, I know it makes a nice smooshy scarf, and -- the BIG upside -- there's no weaving in. You can just knot the ends and hide them on the inside of the tube. The downside is that there's a visible jog in colour changes with this type of continuous knitting, but that can be hidden a bit on the edge of the scarf.