Snow, as far as I know, was supposed to be implemented in Simcity 4, when the terrain was high enough, but, knowing that all things expected can't be in the game with a deadline, it was left out. There are mods out there, as you can see in my cities. I used an added in highway along with the "turning sections" of streets and little cul-de-sac loops. There's also roundabouts that can be placed as well as many other, rather insignificant, modifications to the game to actually make your cities a lot more realistic. There is a mod with snow out there.

Unfortunately, I have yet to see any desert theatres out there.