Heat and rain are bigger barriers to bicycles than cold. You could make a case for ice, but you can address that at the infrastructure level. You can make a case for hills, but again, infrastructure (namely, minimizing grade and going around whenever possible). It's a lot easier to wear a coat than it is to wear an air conditioner; if Tw > 30, you are risking heat stroke by pedaling. California, except the far southeast, has generally cooler and much drier summers than most of the United States.

Also, it's +2 in Umeå right now, which is warmer than I thought.