It's highly subjective, I personally cannot stand temperatures below 15C or so, it's "painful" (yes, I'm a wuss). I haven't lived in Colorado but I did live in

It's highly subjective, I personally cannot stand temperatures below 15C or so, it's "painful" (yes, I'm a wuss). I haven't lived in Colorado but I did live in Europe and recently looked at the climate/temperature tables of Boulder to compare to Bay Area. It rather seems to me that it has weather similar to where I lived in Europe (hot summers, cold winters) with a large variation of daytime/nighttime temperature and a bit drier climate (in Boulder at least) because of the nearby mountains. All in all, lots of days in Boulder where temperature average would be <15C so not that good.