Is it possible to run Windows completely off of a USB 3.0 External HDD?

so I have a Macbook Air and a USB 3.0 7200RPM HDD...

the reason I'm asking whether I can run Windows off of it is because I don't have enough space on my SSD to run two OSes. I only really want to do this because I'd love to be able to play SimCity.

Is the external HDD fast enough to run Windows off of it without a hitch?