I have a theory. This theory is quite simple. This theory is that some type of snowy biome is always touching a desert biome. I do not know if this means that a Taiga always touches a desert (for instance if there is a randomly generated Taiga I do not know if there will always be a desert touching said Taiga.) However, from what I have seen in my countless hours of Minecraft creation is that when there is a randomly generated desert there is always some form of naturally generated taiga touching said desert. These snow biomes are most commonly Taiga, but can also be Ice Hills, Ice Mountains, Ice Plains, etc. Let me know if this theory stands true for you or if you have found a break in it. Happy hunting!