Help with simulating temperature over year. (Seasons and that shebang)

Okay so, for a game I want to develop, you grow crops and the way that the crops grow is determined by the weather (temperature/sunlight and rainfall). I want help with how to get a feasible temperature for any given day, and I will add some randomness on top of this. I'm considering maybe just using a sine wave, but I'm unsure if this is a good or bad idea.

Here's a graph I found of some random northern hemisphere town's temperature throughout the year.

Notice two things
1: The temperatures in this one year follow the general trend of the entire year
2: The line on the graph would not be anywhere near smoothly looping, it is a sharp change at each end of the year.

I think that would be better.

I'm sure somewhere online you can find the actual daily temperatures for a year anyplace they take measurements, and then you can randomize that a little bit. There are only 365 days a year; that wouldn't be too much to store.