I'll be sure to go back through and clean up my code, the site should however be displaying 0 if yesterday at this same time it was also, 73 degrees F, does this seem correct?
No it's not a bug. I had to read it twice. For me it says 10°F warmer and a bit windier than this time yesterday. It's also way clearer than yesterday and it'll be warmer an hour from now. The keyword in that is warmer. So if the temperature is the same as it was a day prior, it would be 0.